15. HQL and JPQL

The Hibernate Query Language (HQL) and Java Persistence Query Language (JPQL) are both object model focused query languages similar in nature to SQL. JPQL is a heavily-inspired-by subset of HQL. A JPQL query is always a valid HQL query, the reverse is not true, however.

Both HQL and JPQL are non-type-safe ways to perform query operations. Criteria queries offer a type-safe approach to querying. See Criteria for more information.

15.1. Example domain model

To better understand the further HQL and JPQL examples, it’s time to familiarize the domain model entities that are used in all the examples features in this chapter.

Example 483. Examples domain model

@NamedQueries({
    @NamedQuery(
        name = "get_person_by_name",
        query = "select p from Person p where name = :name"
    )
    ,
    @NamedQuery(
        name = "get_read_only_person_by_name",
        query = "select p from Person p where name = :name",
        hints = {
            @QueryHint(
                name = "org.hibernate.readOnly",
                value = "true"
            )
        }
    )
})
@NamedStoredProcedureQueries(
    @NamedStoredProcedureQuery(
        name = "sp_person_phones",
        procedureName = "sp_person_phones",
        parameters = {
            @StoredProcedureParameter(
                name = "personId",
                type = Long.class,
                mode = ParameterMode.IN
            ),
            @StoredProcedureParameter(
                name = "personPhones",
                type = Class.class,
                mode = ParameterMode.REF_CURSOR
            )
        }
    )
)
@Entity
public class Person {
    @Id
    @GeneratedValue
    private Long id;
    private String name;
    private String nickName;
    private String address;
    @Temporal(TemporalType.TIMESTAMP )
    private Date createdOn;
    @OneToMany(mappedBy = "person", cascade = CascadeType.ALL)
    @OrderColumn(name = "order_id")
    private List<Phone> phones = new ArrayList<>();
    @ElementCollection
    @MapKeyEnumerated(EnumType.STRING)
    private Map<AddressType, String> addresses = new HashMap<>();
    @Version
    private int version;
    //Getters and setters are omitted for brevity
}
public enum AddressType {
    HOME,
    OFFICE
}
@Entity
public class Partner {
    @Id
    @GeneratedValue
    private Long id;
    private String name;
    @Version
    private int version;
    //Getters and setters are omitted for brevity
}
@Entity
public class Phone {
    @Id
    private Long id;
    @ManyToOne(fetch = FetchType.LAZY)
    private Person person;
    @Column(name = "phone_number")
    private String number;
    @Enumerated(EnumType.STRING)
    @Column(name = "phone_type")
    private PhoneType type;
    @OneToMany(mappedBy = "phone", cascade = CascadeType.ALL, orphanRemoval = true)
    private List<Call> calls = new ArrayList<>(  );
    @OneToMany(mappedBy = "phone")
    @MapKey(name = "timestamp")
    @MapKeyTemporal(TemporalType.TIMESTAMP )
    private Map<Date, Call> callHistory = new HashMap<>();
    @ElementCollection
    private List<Date> repairTimestamps = new ArrayList<>(  );
    //Getters and setters are omitted for brevity
}
public enum PhoneType {
    LAND_LINE,
    MOBILE;
}
@Entity
@Table(name = "phone_call")
public class Call {
    @Id
    @GeneratedValue
    private Long id;
    @ManyToOne
    private Phone phone;
    @Column(name = "call_timestamp")
    private Date timestamp;
    private int duration;
    //Getters and setters are omitted for brevity
}
@Entity
@Inheritance(strategy = InheritanceType.JOINED)
public class Payment {
    @Id
    @GeneratedValue
    private Long id;
    private BigDecimal amount;
    private boolean completed;
    @ManyToOne
    private Person person;
    //Getters and setters are omitted for brevity
}
@Entity
public class CreditCardPayment extends Payment {
}
@Entity
public class WireTransferPayment extends Payment {
}

15.2. Query API

When using Hibernate, you can execute entity queries either via JPA or the Hibernate-specific API. Since 5.2, the Hibernate Session interface extends the JPA EntityManager interface. For this reason, the query API was also merged, and now the Hibernate org.hibernate.query.Query interface extends the JPA javax.persistence.Query.

Next, we are going to see how the query API differs between the standard JPA interfaces and the Hibernate-specific API.

15.2.1. JPA Query API

In JPA, the query is represented by javax.persistence.Query or javax.persistence.TypedQuery as obtained from the EntityManager. The create an inline Query or TypedQuery, you need to use the EntityManager#createQuery method. For named queries, the EntityManager#createNamedQuery method is needed.

Example 484. Obtaining a JPA Query or a TypedQuery reference

Query query = entityManager.createQuery(
    "select p " +
    "from Person p " +
    "where p.name like :name"
);
TypedQuery<Person> typedQuery = entityManager.createQuery(
    "select p " +
    "from Person p " +
    "where p.name like :name", Person.class
);

Example 485. Obtaining a JPA Query or a TypedQuery reference for a named query

@NamedQuery(
    name = "get_person_by_name",
    query = "select p from Person p where name = :name"
)
Query query = entityManager.createNamedQuery( "get_person_by_name" );
TypedQuery<Person> typedQuery = entityManager.createNamedQuery(
    "get_person_by_name", Person.class
);

Hibernate offers a specific @NamedQuery annotation which provides ways to configure various query features, like flush mode, cacheability, time out interval.

Example 486. Obtaining a Hibernate Query or a TypedQuery reference for a named query

@NamedQueries({
    @NamedQuery(
        name = "get_phone_by_number",
        query = "select p " +
                "from Phone p " +
                "where p.number = :number",
        timeout = 1,
        readOnly = true
    )
})
Phone phone = entityManager
    .createNamedQuery( "get_phone_by_number", Phone.class )
    .setParameter( "number", "123-456-7890" )
    .getSingleResult();

The Query interface can then be used to control the execution of the query. For example, we may want to specify an execution timeout or control caching.

Example 487. Basic JPA Query usage

Query query = entityManager.createQuery(
    "select p " +
    "from Person p " +
    "where p.name like :name" )
// timeout - in milliseconds
.setHint( "javax.persistence.query.timeout", 2000 )
// flush only at commit time
.setFlushMode( FlushModeType.COMMIT );

For complete details, see the Query Javadocs. Many of the settings controlling the execution of the query are defined as hints. JPA defines some standard hints (like timeout in the example), but most are provider specific. Relying on provider specific hints limits your applications portability to some degree.

javax.persistence.query.timeout

Defines the query timeout, in milliseconds.

javax.persistence.fetchgraph

Defines a fetchgraph EntityGraph. Attributes explicitly specified as AttributeNodes are treated as FetchType.EAGER (via join fetch or subsequent select). For details, see the EntityGraph discussions in Fetching.

javax.persistence.loadgraph

Defines a loadgraph EntityGraph. Attributes explicitly specified as AttributeNodes are treated as FetchType.EAGER (via join fetch or subsequent select). Attributes that are not specified are treated as FetchType.LAZY or FetchType.EAGER depending on the attribute’s definition in metadata. For details, see the EntityGraph discussions in Fetching.

org.hibernate.cacheMode

Defines the CacheMode to use. See org.hibernate.query.Query#setCacheMode.

org.hibernate.cacheable

Defines whether the query is cacheable. true/false. See org.hibernate.query.Query#setCacheable.

org.hibernate.cacheRegion

For queries that are cacheable, defines a specific cache region to use. See org.hibernate.query.Query#setCacheRegion.

org.hibernate.comment

Defines the comment to apply to the generated SQL. See org.hibernate.query.Query#setComment.

org.hibernate.fetchSize

Defines the JDBC fetch-size to use. See org.hibernate.query.Query#setFetchSize.

org.hibernate.flushMode

Defines the Hibernate-specific FlushMode to use. See org.hibernate.query.Query#setFlushMode. If possible, prefer using javax.persistence.Query#setFlushMode instead.

org.hibernate.readOnly

Defines that entities and collections loaded by this query should be marked as read-only. See org.hibernate.query.Query#setReadOnly.

The final thing that needs to happen before the query can be executed is to bind the values for any defined parameters. JPA defines a simplified set of parameter binding methods. Essentially, it supports setting the parameter value (by name/position) and a specialized form for Calendar/Date types additionally accepting a TemporalType.

Example 488. JPA name parameter binding

Query query = entityManager.createQuery(
    "select p " +
    "from Person p " +
    "where p.name like :name" )
.setParameter( "name", "J%" );
// For generic temporal field types (e.g. `java.util.Date`, `java.util.Calendar`)
// we also need to provide the associated `TemporalType`
Query query = entityManager.createQuery(
    "select p " +
    "from Person p " +
    "where p.createdOn > :timestamp" )
.setParameter( "timestamp", timestamp, TemporalType.DATE );

JPQL-style positional parameters are declared using a question mark followed by an ordinal - ?1, ?2. The ordinals start with 1. Just like with named parameters, positional parameters can also appear multiple times in a query.

Example 489. JPA positional parameter binding

Query query = entityManager.createQuery(
    "select p " +
    "from Person p " +
    "where p.name like ?1" )
.setParameter( 1, "J%" );

In terms of execution, JPA Query offers 3 different methods for retrieving a result set.

• Query#getResultList() - executes the select query and returns back the list of results.

• Query#getResultStream() - executes the select query and returns back a Stream over the results.

• Query#getSingleResult() - executes the select query and returns a single result. If there were more than one result an exception is thrown.

Example 490. JPA getResultList() result

List<Person> persons = entityManager.createQuery(
    "select p " +
    "from Person p " +
    "where p.name like :name" )
.setParameter( "name", "J%" )
.getResultList();

Example 491. JPA getResultStream() result

try(Stream<Person> personStream = entityManager.createQuery(
    "select p " +
    "from Person p " +
    "where p.name like :name", Person.class )
.setParameter( "name", "J%" )
.getResultStream()) {
    List<Person> persons = personStream
        .skip( 5 )
        .limit( 5 )
        .collect( Collectors.toList() );
}

Example 492. JPA getSingleResult()

Person person = (Person) entityManager.createQuery(
    "select p " +
    "from Person p " +
    "where p.name like :name" )
.setParameter( "name", "J%" )
.getSingleResult();

15.2.2. Hibernate Query API

In Hibernate, the HQL query is represented as org.hibernate.query.Query which is obtained from a Session. If the HQL is a named query, Session#getNamedQuery would be used; otherwise Session#createQuery is needed.

Example 493. Obtaining a Hibernate Query

org.hibernate.query.Query query = session.createQuery(
    "select p " +
    "from Person p " +
    "where p.name like :name"
);

Example 494. Obtaining a Hibernate Query reference for a named query

org.hibernate.query.Query query = session.getNamedQuery( "get_person_by_name" );

The Query interface can then be used to control the execution of the query. For example, we may want to specify an execution timeout or control caching.

Example 495. Basic Query usage - Hibernate

org.hibernate.query.Query query = session.createQuery(
    "select p " +
    "from Person p " +
    "where p.name like :name" )
// timeout - in seconds
.setTimeout( 2 )
// write to L2 caches, but do not read from them
.setCacheMode( CacheMode.REFRESH )
// assuming query cache was enabled for the SessionFactory
.setCacheable( true )
// add a comment to the generated SQL if enabled via the hibernate.use_sql_comments configuration property
.setComment( "+ INDEX(p idx_person_name)" );

For complete details, see the Query Javadocs.

Flushing is covered in detail in Flushing. Locking is covered in detail in Locking. The concept of read-only state is covered in Persistence Contexts.

Hibernate also allows an application to hook into the process of building the query results via the org.hibernate.transform.ResultTransformer contract. See its Javadocs as well as the Hibernate-provided implementations for additional details.

The last thing that needs to happen before we can execute the query is to bind the values for any parameters defined in the query. Query defines many overloaded methods for this purpose. The most generic form takes the value as well as the Hibernate Type.

Example 496. Hibernate name parameter binding

org.hibernate.query.Query query = session.createQuery(
    "select p " +
    "from Person p " +
    "where p.name like :name" )
.setParameter( "name", "J%", StringType.INSTANCE );

Hibernate generally understands the expected type of the parameter given its context in the query. In the previous example since we are using the parameter in a LIKE comparison against a String-typed attribute Hibernate would automatically infer the type; so the above could be simplified.

Example 497. Hibernate name parameter binding (inferred type)

org.hibernate.query.Query query = session.createQuery(
    "select p " +
    "from Person p " +
    "where p.name like :name" )
.setParameter( "name", "J%" );

There are also short hand forms for binding common types such as strings, booleans, integers, etc.

Example 498. Hibernate name parameter binding (short forms)

org.hibernate.query.Query query = session.createQuery(
    "select p " +
    "from Person p " +
    "where p.name like :name " +
    "  and p.createdOn > :timestamp" )
.setParameter( "name", "J%" )
.setParameter( "timestamp", timestamp, TemporalType.TIMESTAMP);

org.hibernate.query.Query query = session.createQuery(
    “select p “ +
    “from Person p “ +
    “where p.name like ?” )
.setParameter( 1, “J%” );

In terms of execution, Hibernate offers 4 different methods. The 2 most commonly used are

• Query#list - executes the select query and returns back the list of results.

• Query#uniqueResult - executes the select query and returns the single result. If there were more than one result an exception is thrown.

Example 499. Hibernate list() result

List<Person> persons = session.createQuery(
    "select p " +
    "from Person p " +
    "where p.name like :name" )
.setParameter( "name", "J%" )
.list();

It is also possible to extract a single result from a Query.

Example 500. Hibernate uniqueResult()

Person person = (Person) session.createQuery(
    "select p " +
    "from Person p " +
    "where p.name like :name" )
.setParameter( "name", "J%" )
.uniqueResult();

15.2.3. Query scrolling

Hibernate offers additional, specialized methods for scrolling the query and handling results using a server-side cursor.

Query#scroll works in tandem with the JDBC notion of a scrollable ResultSet.

The Query#scroll method is overloaded:

• The main form accepts a single argument of type org.hibernate.ScrollMode which indicates the type of scrolling to be used. See the Javadocs for the details on each.

• The second form takes no argument and will use the ScrollMode indicated by Dialect#defaultScrollMode.

Query#scroll returns a org.hibernate.ScrollableResults which wraps the underlying JDBC (scrollable) ResultSet and provides access to the results. Unlike a typical forward-only ResultSet, the ScrollableResults allows you to navigate the ResultSet in any direction.

Example 501. Scrolling through a ResultSet containing entities

try ( ScrollableResults scrollableResults = session.createQuery(
        "select p " +
        "from Person p " +
        "where p.name like :name" )
        .setParameter( "name", "J%" )
        .scroll()
) {
    while(scrollableResults.next()) {
        Person person = (Person) scrollableResults.get()[0];
        process(person);
    }
}

Hibernate also supports Query#iterate, which is intended for loading entities when it is known that the loaded entries are already stored in the second-level cache. The idea behind iterate is that just the matching identifiers will be obtained in the SQL query. From these the identifiers are resolved by second-level cache lookup. If these second-level cache lookups fail, additional queries will need to be issued against the database.

The Iterator returned from Query#iterate is actually a specially typed Iterator: org.hibernate.engine.HibernateIterator. It is specialized to expose a close() method (again, inherited from java.io.Closeable). When you are done with this Iterator you should close it, either by casting to HibernateIterator or Closeable, or by calling Hibernate#close(java.util.Iterator).

Since 5.2, Hibernate offers support for returning a Stream which can be later used to transform the underlying ResultSet.

Internally, the stream() behaves like a Query#scroll and the underlying result is backed by a ScrollableResults.

Fetching a projection using the Query#stream method can be done as follows:

Example 502. Hibernate stream() using a projection result type

try ( Stream<Object[]> persons = session.createQuery(
    "select p.name, p.nickName " +
    "from Person p " +
    "where p.name like :name" )
.setParameter( "name", "J%" )
.stream() ) {
    persons
    .map( row -> new PersonNames(
            (String) row[0],
            (String) row[1] ) )
    .forEach( this::process );
}

When fetching a single result, like a Person entity, instead of a Stream<Object[]>, Hibernate is going to figure out the actual type, so the result is a Stream<Person>.

Example 503. Hibernate stream() using an entity result type

try( Stream<Person> persons = session.createQuery(
    "select p " +
    "from Person p " +
    "where p.name like :name" )
.setParameter( "name", "J%" )
.stream() ) {
    Map<Phone, List<Call>> callRegistry = persons
            .flatMap( person -> person.getPhones().stream() )
            .flatMap( phone -> phone.getCalls().stream() )
            .collect( Collectors.groupingBy( Call::getPhone ) );
    process(callRegistry);
}

15.2.4. Query streaming

Since version 2.2, the JPA Query interface offers support for returning a Stream via the getResultStream method.

Just like the scroll method, you can use a try-with-resources block to close the Stream prior to closing the currently running Persistence Context.

Since Hibernate 5.4, the Stream is also closed when calling a terminal operation, as illustrated by the following example.

List<Person> persons = entityManager.createQuery(
        "select p " +
        "from Person p " +
        "where p.name like :name", Person.class )
.setParameter( "name", "J%" )
.getResultStream()
.skip( 5 )
.limit( 5 )
.collect( Collectors.toList() );

The Stream is closed automatically after calling the collect method, since there is no reason to keep the underlying JDBC ResultSet open if the Stream cannot be reused.

15.3. Case Sensitivity

With the exception of names of Java classes and properties, queries are case-insensitive. So SeLeCT is the same as sELEct is the same as SELECT, but org.hibernate.eg.FOO and org.hibernate.eg.Foo are different, as are foo.barSet and foo.BARSET.

15.4. Statement types

Both HQL and JPQL allow SELECT, UPDATE and DELETE statements to be performed. HQL additionally allows INSERT statements, in a form similar to a SQL INSERT FROM SELECT.

15.5. Select statements

The BNF for SELECT statements in HQL is:

select_statement :: =
    [select_clause]
    from_clause
    [where_clause]
    [groupby_clause]
    [having_clause]
    [orderby_clause]

The simplest possible HQL SELECT statement is of the form:

List<Person> persons = session.createQuery(
    "from Person" )
.list();

List<Person> persons = entityManager.createQuery(
    “select p “ +
    “from Person p”, Person.class )
.getResultList();

15.6. Update statements

The BNF for UPDATE statements is the same in HQL and JPQL:

update_statement ::=
    update_clause [where_clause]
update_clause ::=
    UPDATE entity_name [[AS] identification_variable]
    SET update_item {, update_item}*
update_item ::=
    [identification_variable.]{state_field | single_valued_object_field} = new_value
new_value ::=
    scalar_expression | simple_entity_expression | NULL

UPDATE statements, by default, do not affect the version or the timestamp attribute values for the affected entities.

However, you can force Hibernate to set the version or timestamp attribute values through the use of a versioned update. This is achieved by adding the VERSIONED keyword after the UPDATE keyword.

An UPDATE statement is executed using the executeUpdate() of either org.hibernate.query.Query or javax.persistence.Query. The method is named for those familiar with the JDBC executeUpdate() on java.sql.PreparedStatement.

The int value returned by the executeUpdate() method indicates the number of entities affected by the operation. This may or may not correlate to the number of rows affected in the database. An HQL bulk operation might result in multiple actual SQL statements being executed (for joined-subclass, for example). The returned number indicates the number of actual entities affected by the statement. Using a JOINED inheritance hierarchy, a delete against one of the subclasses may actually result in deletes against not just the table to which that subclass is mapped, but also the “root” table and tables “in between”.

Example 504. UPDATE query statements

int updatedEntities = entityManager.createQuery(
    "update Person p " +
    "set p.name = :newName " +
    "where p.name = :oldName" )
.setParameter( "oldName", oldName )
.setParameter( "newName", newName )
.executeUpdate();
int updatedEntities = session.createQuery(
    "update Person " +
    "set name = :newName " +
    "where name = :oldName" )
.setParameter( "oldName", oldName )
.setParameter( "newName", newName )
.executeUpdate();
int updatedEntities = session.createQuery(
    "update versioned Person " +
    "set name = :newName " +
    "where name = :oldName" )
.setParameter( "oldName", oldName )
.setParameter( "newName", newName )
.executeUpdate();

15.7. Delete statements

The BNF for DELETE statements is the same in HQL and JPQL:

delete_statement ::=
    delete_clause [where_clause]
delete_clause ::=
    DELETE FROM entity_name [[AS] identification_variable]

A DELETE statement is also executed using the executeUpdate() method of either org.hibernate.query.Query or javax.persistence.Query.

15.8. Insert statements

HQL adds the ability to define INSERT statements as well.

The BNF for an HQL INSERT statement is:

insert_statement ::=
    insert_clause select_statement
insert_clause ::=
    INSERT INTO entity_name (attribute_list)
attribute_list ::=
    state_field[, state_field ]*

The attribute_list is analogous to the column specification in the SQL INSERT statement. For entities involved in mapped inheritance, only attributes directly defined on the named entity can be used in the attribute_list. Superclass properties are not allowed and subclass properties do not make sense. In other words, INSERT statements are inherently non-polymorphic.

select_statement can be any valid HQL select query, with the caveat that the return types must match the types expected by the insert. Currently, this is checked during query compilation rather than allowing the check to delegate to the database. This may cause problems between Hibernate Types which are equivalent as opposed to equal. For example, this might lead to issues with mismatches between an attribute mapped as a org.hibernate.type.DateType and an attribute defined as a org.hibernate.type.TimestampType, even though the database might not make a distinction or might be able to handle the conversion.

For the id attribute, the insert statement gives you two options. You can either explicitly specify the id property in the attribute_list, in which case its value is taken from the corresponding select expression, or omit it from the attribute_list in which case a generated value is used. This latter option is only available when using id generators that operate “in the database”; attempting to use this option with any “in memory” type generators will cause an exception during parsing.

For optimistic locking attributes, the insert statement again gives you two options. You can either specify the attribute in the attribute_list in which case its value is taken from the corresponding select expressions or omit it from the attribute_list in which case the seed value defined by the corresponding org.hibernate.type.VersionType is used.

Example 505. INSERT query statements

int insertedEntities = session.createQuery(
    "insert into Partner (id, name) " +
    "select p.id, p.name " +
    "from Person p ")
.executeUpdate();

15.9. The FROM clause

The FROM clause is responsible for defining the scope of object model types available to the rest of the query. It is also responsible for defining all the “identification variables” available to the rest of the query.

15.10. Identification variables

Identification variables are often referred to as aliases. References to object model classes in the FROM clause can be associated with an identification variable that can then be used to refer to that type throughout the rest of the query.

In most cases declaring an identification variable is optional, though it is usually good practice to declare them.

An identification variable must follow the rules for Java identifier validity.

According to JPQL, identification variables must be treated as case-insensitive. Good practice says you should use the same case throughout a query to refer to a given identification variable. In other words, JPQL says they can be case-insensitive and so Hibernate must be able to treat them as such, but this does not make it good practice.

15.11. Root entity references

A root entity reference, or what JPA calls a range variable declaration, is specifically a reference to a mapped entity type from the application. It cannot name component/embeddable types. And associations, including collections, are handled in a different manner, as later discussed.

The BNF for a root entity reference is:

root_entity_reference ::=
    entity_name [AS] identification_variable

Example 506. Simple query example

List<Person> persons = entityManager.createQuery(
    "select p " +
    "from org.hibernate.userguide.model.Person p", Person.class )
.getResultList();

We see that the query is defining a root entity reference to the org.hibernate.userguide.model.Person object model type. Additionally, it declares an alias of p to that org.hibernate.userguide.model.Person reference, which is the identification variable.

Usually, the root entity reference represents just the entity name rather than the entity class FQN (fully-qualified name). By default, the entity name is the unqualified entity class name, here Person.

Example 507. Simple query using entity name for root entity reference

List<Person> persons = entityManager.createQuery(
    "select p " +
    "from Person p", Person.class )
.getResultList();

Multiple root entity references can also be specified, even when naming the same entity.

Example 508. Simple query using multiple root entity references

List<Object[]> persons = entityManager.createQuery(
    "select distinct pr, ph " +
    "from Person pr, Phone ph " +
    "where ph.person = pr and ph is not null", Object[].class)
.getResultList();

List<Person> persons = entityManager.createQuery(
    "select distinct pr1 " +
    "from Person pr1, Person pr2 " +
    "where pr1.id <> pr2.id " +
    "  and pr1.address = pr2.address " +
    "  and pr1.createdOn < pr2.createdOn", Person.class )
.getResultList();

15.12. Explicit joins

The FROM clause can also contain explicit relationship joins using the join keyword. These joins can be either inner or left outer style joins.

Example 509. Explicit inner join examples

List<Person> persons = entityManager.createQuery(
    "select distinct pr " +
    "from Person pr " +
    "join pr.phones ph " +
    "where ph.type = :phoneType", Person.class )
.setParameter( "phoneType", PhoneType.MOBILE )
.getResultList();
// same query but specifying join type as 'inner' explicitly
List<Person> persons = entityManager.createQuery(
    "select distinct pr " +
    "from Person pr " +
    "inner join pr.phones ph " +
    "where ph.type = :phoneType", Person.class )
.setParameter( "phoneType", PhoneType.MOBILE )
.getResultList();

Example 510. Explicit left (outer) join examples

List<Person> persons = entityManager.createQuery(
    "select distinct pr " +
    "from Person pr " +
    "left join pr.phones ph " +
    "where ph is null " +
    "   or ph.type = :phoneType", Person.class )
.setParameter( "phoneType", PhoneType.LAND_LINE )
.getResultList();
// functionally the same query but using the 'left outer' phrase
List<Person> persons = entityManager.createQuery(
    "select distinct pr " +
    "from Person pr " +
    "left outer join pr.phones ph " +
    "where ph is null " +
    "   or ph.type = :phoneType", Person.class )
.setParameter( "phoneType", PhoneType.LAND_LINE )
.getResultList();

HQL also defines a WITH clause to qualify the join conditions.

Example 511. HQL WITH clause join example

List<Object[]> personsAndPhones = session.createQuery(
    "select pr.name, ph.number " +
    "from Person pr " +
    "left join pr.phones ph with ph.type = :phoneType " )
.setParameter( "phoneType", PhoneType.LAND_LINE )
.list();

Example 512. JPQL ON clause join example

List<Object[]> personsAndPhones = entityManager.createQuery(
    "select pr.name, ph.number " +
    "from Person pr " +
    "left join pr.phones ph on ph.type = :phoneType " )
.setParameter( "phoneType", PhoneType.LAND_LINE )
.getResultList();

The distinction in this specific example is probably not that significant. The with clause is sometimes necessary for more complicated queries.

Explicit joins may reference association or component/embedded attributes. In the case of component/embedded attributes, the join is simply logical and does not correlate to a physical (SQL) join. For further information about collection-valued association references, see Collection member references.

An important use case for explicit joins is to define FETCH JOINs which override the laziness of the joined association. As an example, given an entity named Person with a collection-valued association named phones, the JOIN FETCH will also load the child collection in the same SQL query:

Example 513. Fetch join example

// functionally the same query but using the 'left outer' phrase
List<Person> persons = entityManager.createQuery(
    "select distinct pr " +
    "from Person pr " +
    "left join fetch pr.phones ", Person.class )
.getResultList();

As you can see from the example, a fetch join is specified by injecting the keyword fetch after the keyword join. In the example, we used a left outer join because we also wanted to return customers who have no orders.

Inner joins can also be fetched, but inner joins filter out the root entity. In the example, using an inner join instead would have resulted in customers without any orders being filtered out of the result.

15.13. Implicit joins (path expressions)

Another means of adding to the scope of object model types available to the query is through the use of implicit joins or path expressions.

Example 514. Simple implicit join example

List<Phone> phones = entityManager.createQuery(
    "select ph " +
    "from Phone ph " +
    "where ph.person.address = :address ", Phone.class )
.setParameter( "address", address )
.getResultList();
// same as
List<Phone> phones = entityManager.createQuery(
    "select ph " +
    "from Phone ph " +
    "join ph.person pr " +
    "where pr.address = :address ", Phone.class )
.setParameter( "address", address)
.getResultList();

An implicit join always starts from an identification variable, followed by the navigation operator ( . ), followed by an attribute for the object model type referenced by the initial identification variable. In the example, the initial identification variable is ph which refers to the Phone entity. The ph.person reference then refers to the person attribute of the Phone entity. person is an association type so we further navigate to its age attribute.

As shown in the example, implicit joins can appear outside the FROM clause. However, they affect the FROM clause.

Example 515. Reused implicit join

List<Phone> phones = entityManager.createQuery(
    "select ph " +
    "from Phone ph " +
    "where ph.person.address = :address " +
    "  and ph.person.createdOn > :timestamp", Phone.class )
.setParameter( "address", address )
.setParameter( "timestamp", timestamp )
.getResultList();
//same as
List<Phone> phones = entityManager.createQuery(
    "select ph " +
    "from Phone ph " +
    "inner join ph.person pr " +
    "where pr.address = :address " +
    "  and pr.createdOn > :timestamp", Phone.class )
.setParameter( "address", address )
.setParameter( "timestamp", timestamp )
.getResultList();

Just as with explicit joins, implicit joins may reference association or component/embedded attributes. For further information about collection-valued association references, see Collection member references.

In the case of component/embedded attributes, the join is simply logical and does not correlate to a physical (SQL) join. Unlike explicit joins, however, implicit joins may also reference basic state fields as long as the path expression ends there.

15.14. Distinct

For JPQL and HQL, DISTINCT has two meanings:

1. It can be passed to the database so that duplicates are removed from a result set

2. It can be used to filter out the same parent entity references when join fetching a child collection

15.14.1. Using DISTINCT with SQL projections

For SQL projections, DISTINCT needs to be passed to the database because the duplicated entries need to be filtered out before being returned to the database client.

Example 516. Using DISTINCT with projection queries example

         List<String> lastNames = entityManager.createQuery(
    "select distinct p.lastName " +
    "from Person p", String.class)
.getResultList();

When running the query above, Hibernate generates the following SQL query:

SELECT DISTINCT
    p.last_name as col_0_0_
FROM person p

For this particular use case, passing the DISTINCT keyword from JPQL/HQL to the database is the right thing to do.

15.14.2. Using DISTINCT with entity queries

DISTINCT can also be used to filter out entity object references when fetching a child association along with the parent entities.

Example 517. Using DISTINCT with entity queries example

List<Person> authors = entityManager.createQuery(
    "select distinct p " +
    "from Person p " +
    "left join fetch p.books", Person.class)
.getResultList();

In this case, DISTINCT is used because there can be multiple Books entities associated with a given Person. If in the database there are 3 Persons in the database and each person has 2 Books, without DISTINCT this query will return 6 Persons since the SQL-level result-set size is given by the number of joined Book records.

However, the DISTINCT keyword is passed to the database as well:

SELECT DISTINCT
    p.id as id1_1_0_,
    b.id as id1_0_1_,
    p.first_name as first_na2_1_0_,
    p.last_name as last_nam3_1_0_,
    b.author_id as author_i3_0_1_,
    b.title as title2_0_1_,
    b.author_id as author_i3_0_0__,
    b.id as id1_0_0__
FROM person p
LEFT OUTER JOIN book b ON p.id=b.author_id

In this case, the DISTINCT SQL keyword is undesirable since it does a redundant result set sorting, as explained in this blog post. To fix this issue, Hibernate 5.2.2 added support for the HINT_PASS_DISTINCT_THROUGH entity query hint:

Example 518. Using DISTINCT with entity queries example

List<Person> authors = entityManager.createQuery(
    "select distinct p " +
    "from Person p " +
    "left join fetch p.books", Person.class)
.setHint( QueryHints.HINT_PASS_DISTINCT_THROUGH, false )
.getResultList();

With this entity query hint, Hibernate will not pass the DISTINCT keyword to the SQL query:

SELECT
    p.id as id1_1_0_,
    b.id as id1_0_1_,
    p.first_name as first_na2_1_0_,
    p.last_name as last_nam3_1_0_,
    b.author_id as author_i3_0_1_,
    b.title as title2_0_1_,
    b.author_id as author_i3_0_0__,
    b.id as id1_0_0__
FROM person p
LEFT OUTER JOIN book b ON p.id=b.author_id

When using the HINT_PASS_DISTINCT_THROUGH entity query hint, Hibernate can still remove the duplicated parent-side entities from the query result.

15.15. Collection member references

References to collection-valued associations actually refer to the values of that collection.

Example 519. Collection references example

List<Phone> phones = entityManager.createQuery(
    "select ph " +
    "from Person pr " +
    "join pr.phones ph " +
    "join ph.calls c " +
    "where pr.address = :address " +
    "  and c.duration > :duration", Phone.class )
.setParameter( "address", address )
.setParameter( "duration", duration )
.getResultList();
// alternate syntax
List<Phone> phones = session.createQuery(
    "select ph " +
    "from Person pr, " +
    "in (pr.phones) ph, " +
    "in (ph.calls) c " +
    "where pr.address = :address " +
    "  and c.duration > :duration" )
.setParameter( "address", address )
.setParameter( "duration", duration )
.list();

In the example, the identification variable ph actually refers to the object model type Phone, which is the type of the elements of the Person#phones association.

The example also shows the alternate syntax for specifying collection association joins using the IN syntax. Both forms are equivalent. Which form an application chooses to use is simply a matter of taste.

15.16. Special case - qualified path expressions

We said earlier that collection-valued associations actually refer to the values of that collection. Based on the type of collection, there are also a set of explicit qualification expressions available.

Example 520. Qualified collection references example

@OneToMany(mappedBy = "phone")
@MapKey(name = "timestamp")
@MapKeyTemporal(TemporalType.TIMESTAMP )
private Map<Date, Call> callHistory = new HashMap<>();
// select all the calls (the map value) for a given Phone
List<Call> calls = entityManager.createQuery(
    "select ch " +
    "from Phone ph " +
    "join ph.callHistory ch " +
    "where ph.id = :id ", Call.class )
.setParameter( "id", id )
.getResultList();
// same as above
List<Call> calls = entityManager.createQuery(
    "select value(ch) " +
    "from Phone ph " +
    "join ph.callHistory ch " +
    "where ph.id = :id ", Call.class )
.setParameter( "id", id )
.getResultList();
// select all the Call timestamps (the map key) for a given Phone
List<Date> timestamps = entityManager.createQuery(
    "select key(ch) " +
    "from Phone ph " +
    "join ph.callHistory ch " +
    "where ph.id = :id ", Date.class )
.setParameter( "id", id )
.getResultList();
// select all the Call and their timestamps (the 'Map.Entry') for a given Phone
List<Map.Entry<Date, Call>> callHistory = entityManager.createQuery(
    "select entry(ch) " +
    "from Phone ph " +
    "join ph.callHistory ch " +
    "where ph.id = :id " )
.setParameter( "id", id )
.getResultList();
// Sum all call durations for a given Phone of a specific Person
Long duration = entityManager.createQuery(
    "select sum(ch.duration) " +
    "from Person pr " +
    "join pr.phones ph " +
    "join ph.callHistory ch " +
    "where ph.id = :id " +
    "  and index(ph) = :phoneIndex", Long.class )
.setParameter( "id", id )
.setParameter( "phoneIndex", phoneIndex )
.getSingleResult();

VALUE

Refers to the collection value. Same as not specifying a qualifier. Useful to explicitly show intent. Valid for any type of collection-valued reference.

INDEX

According to HQL rules, this is valid for both Maps and Lists which specify a javax.persistence.OrderColumn annotation to refer to the Map key or the List position (aka the OrderColumn value). JPQL however, reserves this for use in the List case and adds KEY for the Map case. Applications interested in JPA provider portability should be aware of this distinction.

KEY

Valid only for Maps. Refers to the map’s key. If the key is itself an entity, it can be further navigated.

ENTRY

Only valid for Maps. Refers to the map’s logical java.util.Map.Entry tuple (the combination of its key and value). ENTRY is only valid as a terminal path and it’s applicable to the SELECT clause only.

See Collection-related expressions for additional details on collection-related expressions.

15.17. Polymorphism

HQL and JPQL queries are inherently polymorphic.

List<Payment> payments = entityManager.createQuery(
    "select p " +
    "from Payment p ", Payment.class )
.getResultList();

This query names the Payment entity explicitly. However, all subclasses of Payment are also available to the query. So, if the CreditCardPayment and WireTransferPayment entities extend the Payment class, all three types would be available to the entity query, and the query would return instances of all three.

This behavior can be altered in two ways:

• by limiting the query to select only from the subclass entity.

• by using either the org.hibernate.annotations.Polymorphism annotation (global, and Hibernate-specific). See the @Polymorphism section for more info about this use case.

15.18. Expressions

Essentially, expressions are references that resolve to basic or tuple values.

15.19. Identification variable

See The FROM clause.

15.20. Path expressions

Again, see The FROM clause.

15.21. Literals

String literals are enclosed in single quotes. To escape a single quote within a string literal, use double single quotes.

Example 521. String literals examples

List<Person> persons = entityManager.createQuery(
    "select p " +
    "from Person p " +
    "where p.name like 'Joe'", Person.class)
.getResultList();
// Escaping quotes
List<Person> persons = entityManager.createQuery(
    "select p " +
    "from Person p " +
    "where p.name like 'Joe''s'", Person.class)
.getResultList();

Numeric literals are allowed in a few different forms.

Example 522. Numeric literal examples

// simple integer literal
Person person = entityManager.createQuery(
    "select p " +
    "from Person p " +
    "where p.id = 1", Person.class)
.getSingleResult();
// simple integer literal, typed as a long
Person person = entityManager.createQuery(
    "select p " +
    "from Person p " +
    "where p.id = 1L", Person.class)
.getSingleResult();
// decimal notation
List<Call> calls = entityManager.createQuery(
    "select c " +
    "from Call c " +
    "where c.duration > 100.5", Call.class )
.getResultList();
// decimal notation, typed as a float
List<Call> calls = entityManager.createQuery(
    "select c " +
    "from Call c " +
    "where c.duration > 100.5F", Call.class )
.getResultList();
// scientific notation
List<Call> calls = entityManager.createQuery(
    "select c " +
    "from Call c " +
    "where c.duration > 1e+2", Call.class )
.getResultList();
// scientific notation, typed as a float
List<Call> calls = entityManager.createQuery(
    "select c " +
    "from Call c " +
    "where c.duration > 1e+2F", Call.class )
.getResultList();

15.22. Arithmetic

Arithmetic operations also represent valid expressions.

Example 523. Numeric arithmetic examples

// select clause date/time arithmetic operations
Long duration = entityManager.createQuery(
    "select sum(ch.duration) * :multiplier " +
    "from Person pr " +
    "join pr.phones ph " +
    "join ph.callHistory ch " +
    "where ph.id = 1L ", Long.class )
.setParameter( "multiplier", 1000L )
.getSingleResult();
// select clause date/time arithmetic operations
Integer years = entityManager.createQuery(
    "select year( current_date() ) - year( p.createdOn ) " +
    "from Person p " +
    "where p.id = 1L", Integer.class )
.getSingleResult();
// where clause arithmetic operations
List<Person> persons = entityManager.createQuery(
    "select p " +
    "from Person p " +
    "where year( current_date() ) - year( p.createdOn ) > 1", Person.class )
.getResultList();

The following rules apply to the result of arithmetic operations:

• If either of the operands is Double/double, the result is a Double

• else, if either of the operands is Float/float, the result is a Float

• else, if either operand is BigDecimal, the result is BigDecimal

• else, if either operand is BigInteger, the result is BigInteger (except for division, in which case the result type is not further defined)

• else, if either operand is Long/long, the result is Long (except for division, in which case the result type is not further defined)

• else, (the assumption being that both operands are of integral type) the result is Integer (except for division, in which case the result type is not further defined)

Date arithmetic is also supported, albeit in a more limited fashion. This is due to differences in database support and partly to the lack of support for INTERVAL definition in the query language itself.

15.23. Concatenation (operation)

HQL defines a concatenation operator in addition to supporting the concatenation (CONCAT) function. This is not defined by JPQL, so portable applications should avoid its use. The concatenation operator is taken from the SQL concatenation operator (e.g ||).

Example 524. Concatenation operation example

String name = entityManager.createQuery(
    "select 'Customer ' || p.name " +
    "from Person p " +
    "where p.id = 1", String.class )
.getSingleResult();

See Scalar functions for details on the concat() function.

15.24. Aggregate functions

Aggregate functions are also valid expressions in HQL and JPQL. The semantics is the same as their SQL counterpart. The supported aggregate functions are:

COUNT (including distinct/all qualifiers)

The result type is always Long.

AVG

The result type is always Double.

MIN

The result type is the same as the argument type.

MAX

The result type is the same as the argument type.

SUM

The result type of the SUM() function depends on the type of the values being summed. For integral values (other than BigInteger), the result type is Long.

For floating point values (other than BigDecimal) the result type is Double. For BigInteger values, the result type is BigInteger. For BigDecimal values, the result type is BigDecimal.

Example 525. Aggregate function examples

Object[] callStatistics = entityManager.createQuery(
    "select " +
    "    count(c), " +
    "    sum(c.duration), " +
    "    min(c.duration), " +
    "    max(c.duration), " +
    "    avg(c.duration)  " +
    "from Call c ", Object[].class )
.getSingleResult();
Long phoneCount = entityManager.createQuery(
    "select count( distinct c.phone ) " +
    "from Call c ", Long.class )
.getSingleResult();
List<Object[]> callCount = entityManager.createQuery(
    "select p.number, count(c) " +
    "from Call c " +
    "join c.phone p " +
    "group by p.number", Object[].class )
.getResultList();

Aggregations often appear with grouping. For information on grouping see Group by.

15.25. Scalar functions

Both HQL and JPQL define some standard functions that are available regardless of the underlying database in use. HQL can also understand additional functions defined by the Dialect as well as the application.

15.26. JPQL standardized functions

Here is the list of functions defined as supported by JPQL. Applications interested in remaining portable between JPA providers should stick to these functions.

CONCAT

String concatenation function. Variable argument length of 2 or more string values to be concatenated together.

List<String> callHistory = entityManager.createQuery(
    "select concat( p.number, ' : ' , cast(c.duration as string) ) " +
    "from Call c " +
    "join c.phone p", String.class )
.getResultList();

SUBSTRING

Extracts a portion of a string value. The second argument denotes the starting position, where 1 is the first character of the string. The third (optional) argument denotes the length.

List<String> prefixes = entityManager.createQuery(
    "select substring( p.number, 1, 2 ) " +
    "from Call c " +
    "join c.phone p", String.class )
.getResultList();

UPPER

Upper cases the specified string.

List<String> names = entityManager.createQuery(
    "select upper( p.name ) " +
    "from Person p ", String.class )
.getResultList();

LOWER

Lower cases the specified string.

List<String> names = entityManager.createQuery(
    "select lower( p.name ) " +
    "from Person p ", String.class )
.getResultList();

TRIM

Follows the semantics of the SQL trim function.

List<String> names = entityManager.createQuery(
    "select trim( p.name ) " +
    "from Person p ", String.class )
.getResultList();

LENGTH

Returns the length of a string.

List<Integer> lengths = entityManager.createQuery(
    "select length( p.name ) " +
    "from Person p ", Integer.class )
.getResultList();

LOCATE

Locates a string within another string. The third argument (optional) is used to denote a position from which to start looking.

List<Integer> sizes = entityManager.createQuery(
    "select locate( 'John', p.name ) " +
    "from Person p ", Integer.class )
.getResultList();

ABS

Calculates the mathematical absolute value of a numeric value.

List<Integer> abs = entityManager.createQuery(
    "select abs( c.duration ) " +
    "from Call c ", Integer.class )
.getResultList();

MOD

Calculates the remainder of dividing the first argument by the second.

List<Integer> mods = entityManager.createQuery(
    "select mod( c.duration, 10 ) " +
    "from Call c ", Integer.class )
.getResultList();

SQRT

Calculates the mathematical square root of a numeric value.

List<Double> sqrts = entityManager.createQuery(
    "select sqrt( c.duration ) " +
    "from Call c ", Double.class )
.getResultList();

CURRENT_DATE

Returns the database current date.

List<Call> calls = entityManager.createQuery(
    "select c " +
    "from Call c " +
    "where c.timestamp = current_date", Call.class )
.getResultList();

CURRENT_TIME

Returns the database current time.

List<Call> calls = entityManager.createQuery(
    "select c " +
    "from Call c " +
    "where c.timestamp = current_time", Call.class )
.getResultList();

CURRENT_TIMESTAMP

Returns the database current timestamp.

List<Call> calls = entityManager.createQuery(
    "select c " +
    "from Call c " +
    "where c.timestamp = current_timestamp", Call.class )
.getResultList();

15.27. HQL functions

Beyond the JPQL standardized functions, HQL makes some additional functions available regardless of the underlying database in use.

BIT_LENGTH

Returns the length of binary data.

List<Number> bits = entityManager.createQuery(
    "select bit_length( c.duration ) " +
    "from Call c ", Number.class )
.getResultList();

CAST

Performs a SQL cast. The cast target should name the Hibernate mapping type to use. See the data types chapter on for more information.

List<String> durations = entityManager.createQuery(
    "select cast( c.duration as string ) " +
    "from Call c ", String.class )
.getResultList();

EXTRACT

Performs a SQL extraction on datetime values. An extraction extracts parts of the datetime (the year, for example).

List<Integer> years = entityManager.createQuery(
    "select extract( YEAR from c.timestamp ) " +
    "from Call c ", Integer.class )
.getResultList();

See the abbreviated forms below.

YEAR

Abbreviated extract form for extracting the year.

List<Integer> years = entityManager.createQuery(
    "select year( c.timestamp ) " +
    "from Call c ", Integer.class )
.getResultList();

MONTH

Abbreviated extract form for extracting the month.

DAY

Abbreviated extract form for extracting the day.

HOUR

Abbreviated extract form for extracting the hour.

MINUTE

Abbreviated extract form for extracting the minute.

SECOND

Abbreviated extract form for extracting the second.

STR

Abbreviated form for casting a value as character data.

List<String> timestamps = entityManager.createQuery(
    "select str( c.timestamp ) " +
    "from Call c ", String.class )
.getResultList();
List<String> timestamps = entityManager.createQuery(
    "select str( cast(duration as float) / 60, 4, 2 ) " +
    "from Call c ", String.class )
.getResultList();

15.28. User-defined functions

Hibernate Dialects can register additional functions known to be available for that particular database product. These functions are also available in HQL (and JPQL, though only when using Hibernate as the JPA provider, obviously). However, they would only be available when using that database Dialect. Applications that aim for database portability should avoid using functions in this category.

Application developers can also supply their own set of functions. This would usually represent either user-defined SQL functions or aliases for snippets of SQL. Such function declarations are made by using the addSqlFunction() method of the org.hibernate.boot.MetadataBuilder or the legacy org.hibernate.cfg.Configuration.

Now, let’s assume we have the following apply_vat PostgreSQL user-defined function:

Example 526. PostgreSQL user-defined function

statement.executeUpdate(
    "CREATE OR REPLACE FUNCTION apply_vat(integer) RETURNS integer " +
    "   AS 'select cast(($1 * 1.2) as integer);' " +
    "   LANGUAGE SQL " +
    "   IMMUTABLE " +
    "   RETURNS NULL ON NULL INPUT;"
);

Let’s consider we have persisted the following entity in our database:

Example 527. Book entity

Book book = new Book();
book.setIsbn( "978-9730228236" );
book.setTitle( "High-Performance Java Persistence" );
book.setAuthor( "Vlad Mihalcea" );
book.setPriceCents( 4500 );
entityManager.persist( book );

15.28.1. User-defined functions referenced in the WHERE clause

By default, Hibernate can pass through any user-defined function that’s being used in the WHERE clause of a JPQL/HQL entity query.

Example 528. User-defined function passing through the WHERE clause

List<Book> books = entityManager.createQuery(
    "select b " +
    "from Book b " +
    "where apply_vat(b.priceCents) = :price ", Book.class )
.setParameter( "price", 5400 )
.getResultList();
assertTrue( books
    .stream()
    .filter( book -> "High-Performance Java Persistence".equals( book.getTitle() ) )
    .findAny()
    .isPresent()
);

While this works just fine with Hibernate, it might be a problem with other JPA providers. For this purpose, JPA offers the function JPQL keyword which works as follows.

Example 529. Using the JPQL function keyword

List<Book> books = entityManager.createQuery(
    "select b " +
    "from Book b " +
    "where function('apply_vat', b.priceCents) = :price ", Book.class )
.setParameter( "price", 5400 )
.getResultList();
assertTrue( books
    .stream()
    .filter( book -> "High-Performance Java Persistence".equals( book.getTitle() ) )
    .findAny()
    .isPresent()
);

15.28.2. User-defined functions referenced in the SELECT clause

When the user-defined function is referenced in the SELECT clause of a JPQL/HQL entity query, Hibernate can no longer pass it through unless the function is registered.

Example 530. Registering a user-defined function using the MetadataBuilderContributor

settings.put( "hibernate.metadata_builder_contributor",
    (MetadataBuilderContributor) metadataBuilder ->
        metadataBuilder.applySqlFunction(
            "apply_vat",
            new StandardSQLFunction(
                "apply_vat",
                StandardBasicTypes.INTEGER
            )
        )
);

Now that that apply_vat is registered, we can reference it in the JPQL SELECT clause.

Example 531. User-defined function in the SELECT clause

List<Tuple> books = entityManager.createQuery(
    "select b.title as title, apply_vat(b.priceCents) as price " +
    "from Book b " +
    "where b.author = :author ", Tuple.class )
.setParameter( "author", "Vlad Mihalcea" )
.getResultList();
assertEquals( 1, books.size() );
Tuple book = books.get( 0 );
assertEquals( "High-Performance Java Persistence", book.get( "title" ) );
assertEquals( 5400, ((Number) book.get( "price" )).intValue() );

15.29. Collection-related expressions

There are a few specialized expressions for working with collection-valued associations. Generally, these are just abbreviated forms or other expressions for the sake of conciseness.

SIZE

Calculate the size of a collection. Equates to a subquery!

MAXELEMENT

Available for use on collections of basic type. Refers to the maximum value as determined by applying the max SQL aggregation.

MAXINDEX

Available for use on indexed collections. Refers to the maximum index (key/position) as determined by applying the max SQL aggregation.

MINELEMENT

Available for use on collections of basic type. Refers to the minimum value as determined by applying the min SQL aggregation.

MININDEX

Available for use on indexed collections. Refers to the minimum index (key/position) as determined by applying the min SQL aggregation.

ELEMENTS

Used to refer to the elements of a collection as a whole. Only allowed in the where clause. Often used in conjunction with ALL, ANY or SOME restrictions.

INDICES

Similar to elements except that the indices expression refers to the collections indices (keys/positions) as a whole.

Example 532. Collection-related expressions examples

List<Phone> phones = entityManager.createQuery(
    "select p " +
    "from Phone p " +
    "where maxelement( p.calls ) = :call", Phone.class )
.setParameter( "call", call )
.getResultList();
List<Phone> phones = entityManager.createQuery(
    "select p " +
    "from Phone p " +
    "where minelement( p.calls ) = :call", Phone.class )
.setParameter( "call", call )
.getResultList();
List<Person> persons = entityManager.createQuery(
    "select p " +
    "from Person p " +
    "where maxindex( p.phones ) = 0", Person.class )
.getResultList();
// the above query can be re-written with member of
List<Person> persons = entityManager.createQuery(
    "select p " +
    "from Person p " +
    "where :phone member of p.phones", Person.class )
.setParameter( "phone", phone )
.getResultList();
List<Person> persons = entityManager.createQuery(
    "select p " +
    "from Person p " +
    "where :phone = some elements ( p.phones )", Person.class )
.setParameter( "phone", phone )
.getResultList();
List<Person> persons = entityManager.createQuery(
    "select p " +
    "from Person p " +
    "where exists elements ( p.phones )", Person.class )
.getResultList();
List<Phone> phones = entityManager.createQuery(
    "select p " +
    "from Phone p " +
    "where current_date() > key( p.callHistory )", Phone.class )
.getResultList();
List<Phone> phones = entityManager.createQuery(
    "select p " +
    "from Phone p " +
    "where current_date() > all elements( p.repairTimestamps )", Phone.class )
.getResultList();
List<Person> persons = entityManager.createQuery(
    "select p " +
    "from Person p " +
    "where 1 in indices( p.phones )", Person.class )
.getResultList();
List<Person> persons = entityManager.createQuery(
    "select p " +
    "from Person p " +
    "where size( p.phones ) = 2", Person.class )
.getResultList();