Criteria Objects

When you are creating dynamic SQL for SELECT, UPDATE or DELETE, you might have to write complex WHERE statements.

Building these statements using string concentanation is possible but it is tedious to avoid syntax errors and opens your code to SQL injection attacks.

Using parameters might solve SQL injection problems but it involves too much manual work to add parameters.

Luckily, Serenity has a criteria system that helps you build parameterized queries with a syntax similar LINQ expression trees.

Serenity criterias are implemented by utilitizing operator overloading features of C#, unlike LINQ which uses expression trees.

Let’s write a basic SQL where statement as string first:

new SqlQuery()
    .From("MyTable")
    .Select("Name")
    .Where("Month > 5 AND Year < 2015 AND Name LIKE N'%a%'")

and same statement using criteria objects:

new SqlQuery()
    .From("MyTable")
    .Select("Name")
    .Where(
        new Criteria("Month") > 5 &
        new Criteria("Year") < 4 &
        new Criteria("Name").Contains("a")

It looks a bit longer, but it uses parameters

SELECT 
    Name
FROM
    MyTable
WHERE
    Month > @p1 AND
    Year < @p2 AND
    Name LIKE N'%a%'

and you could write it with intellisense if you had an entity:

var m = MyTableRow.Fields;
new SqlQuery()
    .From(m)
    .Select(m.Name)
    .Where(
        m.Month > 5 &
        m.Year < 4 &
        m.Name.Contains("a")

Here we didn’t have to use new Criteria() because field objects also has operator overloads that builds criteria.

BaseCriteria Object

BaseCriteria is the base class for all types of criteria objects.

It has overloads for several C# operators, including >, <, &, | that can be used to build complex criteria using C# expressions.

BaseCriteria doesn’t have a constructor of itself
so you need to create one of the objects that derive from it. Criteria is the most common one that you might use.

Criteria Object

Criteria is a simple object that contains an SQL expression as a string, which is usually a field name.

new Criteria("MyField")

It can also contain an SQL expression (though not recommended this way)

new Criteria("a + b")

This parameter is not syntax checked, so it is possible to build a criteria with invalid expression:

new Criteria("Some invalid expression()///''^')

AND (&) Operator

It is possible to AND two criteria objects with C# & operator:

new Criteria("Field1 > 5") &
new Criteria("Field2 < 4")
`

Please notice that we are not using shortcircuit && operator here.

This creates a new criteria object (BinaryCriteria) with operator (AND) and reference to these two criterias. It doesn’t modify original criteria objects.

BinaryCriteria is similar to BinaryExpression in expression trees

It’s SQL output would be:

Field1 > 5 AND Field2 < 4

It is also possible to use C# &= operator:

BaseCriteria c = new Criteria("Field1 > 5)";
c &= new Criteria("Field2 < 4")

BaseCriteria is the base class for all criteria object types. If we used Criteria c = … in the first line, we would have a compile time error on second line as & operator returns a BinaryCriteria object, which is not assignable to a Criteria object.

OR (|) Operator

This is similar to AND operator, though it uses OR.

new Criteria("Field1 > 5") |
new Criteria("Field2 < 4")
`

Field1 > 5 OR Field2 < 4

Parenthesis Operator (~)

When you are using several AND/OR statements, you might want to put paranthesis.

new Criteria("Field1 > 5") &
(new Criteria("Field2 > 7") | new Criteria("Field2 < 3"))

But this won’t work with criteria objects, as output of above criteria would be:

Field1 > 5 AND Field2 > 7 OR Field2 < 3

Information here applies to Serenity versions before 1.9.8. After this version Serenity puts paranthesis around all binary criteria (AND OR etc) even if you don’t use paranthesis.

So only use ~ if you want to put an explicit parenthesis somewhere.

What happened to our paranthesis? Let’s try putting more paranthesis.

new Criteria("Field1 > 5") &
((((new Criteria("Field2 > 7") | new Criteria("Field2 < 3")))))

Still:

Field1 > 5 AND Field2 > 7 OR Field2 < 3

C# doesn’t provide a way to overload paranthesis, it just uses them to determine calculation order, so Serenity criteria has no idea if you used them with paranthesis or not.

We have to use a special operator, ~ (which is actually two’s complement in C#):

new Criteria("Field1 > 5") &
~(new Criteria("Field2 > 7") | new Criteria("Field2 < 3"))

Now SQL looks like we hoped before:

Field1 > 5 AND (Field2 > 7 OR Field2 < 3)

As Serenity 1.9.8+ auto paranthesis binary criteria, above expression would actually be:

(Field1 > 5) AND (((Field2 > 7) OR (Field2 < 3)))

Comparison Operators (>, >=, <, <=, ==, !=)

The most of C# comparison operators are overloaded, so you can use them as is with criteria.

new Criteria("Field1") == new Criteria("1") &
new Criteria("Field2") != new Criteria("2") &
new Criteria("Field3") > new Criteria("3") &
new Criteria("Field4") >= new Criteria("4") &
new Criteria("Field5") < new Criteria("5") &
new Criteria("Field6") <= new Criteria("6")

Field1 == 1 AND
Field2 <> 2 AND
Field3 > 3 AND
Field4 >= 4 AND
Field5 < 5 AND
Field6 <= 6

Inline Values

When one side of a comparison operator is a criteria and other side is an integer, string, date, guid etc. value, it is converted a parameter criteria.

new Criteria("Field1") == 1 &
new Criteria("Field2") != "ABC" &
new Criteria("Field3") > DateTime.Now &
new Criteria("Field4") >= Guid.NewGuid() &
new Criteria("Field5") < 5L

Field1 == @p1 AND
Field2 <> @p2 AND
Field3 > @p3 AND
Field4 >= @p4 AND
Field5 < @p5

These parameters has corresponding values, when a query containing this criteria is sent to SQL.

Automatic parameter numbering starts from 1 by default, but last number is stored in the query the criteria is used with, so numbers might change.

Let’s use this criteria in a query:

new SqlQuery()
    .From("MyTable")
    .Select("Field999")
    .Where(new Criteria("FirstOne") >= 999)
    .Where(new Criteria("SecondOne") >= 999)
    .Where(
        new Criteria("Field1") == 1 &
        new Criteria("Field2") != "ABC" &
        new Criteria("Field3") > DateTime.Now &
        new Criteria("Field4") >= Guid.NewGuid() &
        new Criteria("Field5") < 5L
    )

SELECT 
  Field999
FROM
  MyTable
WHERE
  FirstOne >= @p1 AND -- @p1 = 999
  SecondOne >= @p2 AND -- @p2 = 999
  Field1 == @p3 AND -- @p3 = 1
  Field2 <> @p4 AND -- @p4 = N'ABC'
  Field3 > @p5 AND -- @p5 = '2016-01-31T01:16:23'
  Field4 >= @p6 AND -- @p6 = '23123-DEFCD-....'
  Field5 < @p7 -- @p7 = 5

Here the same criteria that listed before, used parameter numbers starting from 3, instead of 1. Because prior 2 numbers where used for other WHERE statements coming before it.

So parameter numbering uses the query as context. You shouldn’t make assumptions about what parameter name will be.

ParamCriteria and Explicit Param Names

If you want to use some explicitly named parameter, you can make use of ParamCriteria:

new SqlQuery()
    .From("SomeTable")
    .Select("SomeField")
    .Where(new Criteria("SomeField") <= new ParamCriteria("@myparam"))
    .Where(new Criteria("SomeOtherField") == new ParamCriteria("@myparam"))
    .SetParam("@myparam", 5);

Here we set param value using SetParam extension of SqlQuery.

We could also declare this param beforehand and reuse it:

var myParam = new ParamCriteria("@myparam");
new SqlQuery()
    .From("SomeTable")
    .Select("SomeField")
    .Where(new Criteria("SomeField") <= myParam)
    .Where(new Criteria("SomeOtherField") == myParam)
    .SetParam(myParam.Name, 5);

ConstantCriteria

If you don’t want to use parameterized queries, you may put your values as ConstantCriteria objects. They will not be converted to auto parameters.

new SqlQuery()
    .From("MyTable")
    .Select("MyField")
    .Where(
        new Criteria("Field1") == new ConstantCriteria(1) &
        new Criteria("Field2") != new ConstantCriteria("ABC")
    )

SELECT 
  MyField
FROM
  MyTable
WHERE
  FirstOne >= 1
  SecondOne >= N'ABC'

Null Comparison

In SQL, comparing against NULL values using operators like ==, != returns NULL. You should use IS NULL or IS NOT NULL for such comparisons.

Criteria objects don’t overload comparisons against null (or object), so you may get errors if you try to write expressions like below:

new Criteria("a") == null; // what is type of null?
int b? = null;
new Criteria("c") == b; // no overload for nullable types

These could be written using IsNull and Nullable.Value methods:

new Criteria("a").IsNull();
new Criteria("a").IsNotNull();
int? b = 5;
new Criteria("c") == b.Value;

If you are desperate to write Field = NULL, you could do this:

new Criteria("Field") == new Criteria("NULL")

LIKE Operators

Criteria has methods Like, NotLike, StartsWith, EndsWith, Contains, NotContains to help with LIKE operations.

new Criteria("a").Like("__C%") &
new Criteria("b").NotLike("D%") &
new Criteria("c").StartsWith("S") &
new Criteria("d").EndsWith("X") &
new Criteria("e").Contains("This") &
new Criteria("f").NotContains("That")

a LIKE @p1 AND -- @p1 = N'__C%'
b NOT LIKE @p2 AND -- @p2 = N'D%'
c LIKE @p3 AND -- @p3 = 'S%'
d LIKE @p4 AND -- @p4 = N'%X'
e LIKE @p5 AND -- @p5 = N'%This%'
f NOT LIKE @p6 -- @p6 = N'%That%'

IN and NOT IN Operators

Use an inline array to use IN or NOT IN:

new Criteria("A").In(1, 2, 3, 4, 5)

A IN (@p1, @p2, @p3, @p4, @p5) 
-- @p1 = 1, @p2 = 2, @p3 = 3, @p4 = 4, @p5 = 5

new Criteria("A").NotIn(1, 2, 3, 4, 5)

A NOT IN (@p1, @p2, @p3, @p4, @p5)
-- @p1 = 1, @p2 = 2, @p3 = 3, @p4 = 4, @p5 = 5

You may also pass any enumerable to IN method:

IEnumerable<int> x = new int[] { 1, 3, 5, 7, 9 };
new Criteria("A").In(x);

A IN (1, 3, 5, 7, 9)
-- @p1 = 1, @p2 = 3, @p3 = 5, @p4 = 7, @p5 = 9

It is also possible to use a subquery:

var query = new SqlQuery()
    .From("MyTable")
    .Select("MyField");
query.Where("SomeID").In(
    query.SubQuery()
        .From("SomeTable")
        .Select("SomeID")
        .Where(new Criteria("Balance") < 0));

SELECT 
  MyField
FROM
  MyTable
WHERE
  SomeID IN (
    SELECT 
        SomeID 
    FROM
        SomeTable
    WHERE
        Balance < @p1 -- @p1 = 0
  )

NOT Operator

Use C# ! (not) operator to use NOT:

!(new Criteria("a") >= 5)

NOT (a >= @p1) -- @p1 = 5

Usage with Field Objects

We have used Criteria object constructor so far to build criteria. Field objects also has similar overloads, so they can be used in place of them.

For example, using Order, Detail and Customer rows from Northwind sample:

    var o = OrderRow.Fields.As("o");
    var od = OrderDetailRow.Fields.As("od");
    var c = CustomerRow.Fields.As("c");
    var query = new SqlQuery()
        .From(o)
        .Select(o.CustomerID);
    query.Where(
        o.CustomerCountry == "France" &
        o.ShippingState == 1 &
        o.CustomerID.In(
            query.SubQuery()
                .From(c)
                .Select(c.CustomerID)
                .Where(c.Region == "North")) &
        new Criteria(
            query.SubQuery()
                .From(od)
                .Select(Sql.Sum(od.LineTotal.Expression))
                .Where(od.OrderID == o.OrderID)) >= 1000);

Its output would be:

SELECT 
    o.CustomerID AS [CustomerID] 
FROM 
    Orders o 
LEFT JOIN 
    Customers o_c ON (o_c.CustomerID = o.CustomerID) 
WHERE 
    o_c.[Country] = @p2
    AND (CASE WHEN 
        o.[ShippedDate] IS NULL THEN 0
     ELSE 1 
     END) = @p3 
    AND o.CustomerID IN (
        SELECT 
            c.CustomerID AS [CustomerID] 
        FROM 
            Customers c 
        WHERE 
            c.Region = @p1) 
    AND (SELECT 
        SUM((od.[UnitPrice] * od.[Quantity] - od.[Discount])) 
     FROM
        [Order Details] od 
     WHERE 
        od.OrderID = o.OrderID) >= @p4