检索单个对象

GORM 提供了 First、Take、Last 方法，以便从数据库中检索单个对象。当查询数据库时它添加了 LIMIT 1 条件，且没有找到记录时，它会返回 ErrRecordNotFound 错误

  1. // 获取第一条记录（主键升序）
  2. db.First(&user)
  3. // SELECT * FROM users ORDER BY id LIMIT 1;
  5. // 获取一条记录，没有指定排序字段
  6. db.Take(&user)
  7. // SELECT * FROM users LIMIT 1;
  9. // 获取最后一条记录（主键降序）
  10. db.Last(&user)
  11. // SELECT * FROM users ORDER BY id DESC LIMIT 1;
  13. result := db.First(&user)
  14. result.RowsAffected // 返回找到的记录数
  15. result.Error        // returns error or nil
  17. // 检查 ErrRecordNotFound 错误
  18. errors.Is(result.Error, gorm.ErrRecordNotFound)

如果你想避免ErrRecordNotFound错误，你可以使用Find，比如db.Limit(1).Find(&user)，Find方法可以接受struct和slice的数据。

对单个对象使用Find而不带limit，db.Find(&user)将会查询整个表并且只返回第一个对象，这是性能不高并且不确定的。

The First and Last methods will find the first and last record (respectively) as ordered by primary key. They only work when a pointer to the destination struct is passed to the methods as argument or when the model is specified using db.Model(). Additionally, if no primary key is defined for relevant model, then the model will be ordered by the first field. For example:

  1. var user User
  2. var users []User
  4. // works because destination struct is passed in
  5. db.First(&user)
  6. // SELECT * FROM `users` ORDER BY `users`.`id` LIMIT 1
  8. // works because model is specified using `db.Model()`
  9. result := map[string]interface{}{}
  10. db.Model(&User{}).First(&result)
  11. // SELECT * FROM `users` ORDER BY `users`.`id` LIMIT 1
  13. // doesn't work
  14. result := map[string]interface{}{}
  15. db.Table("users").First(&result)
  17. // works with Take
  18. result := map[string]interface{}{}
  19. db.Table("users").Take(&result)
  21. // no primary key defined, results will be ordered by first field (i.e., `Code`)
  22. type Language struct {
  23.   Code string
  24.   Name string
  25. }
  26. db.First(&Language{})
  27. // SELECT * FROM `languages` ORDER BY `languages`.`code` LIMIT 1

根据主键检索

Objects can be retrieved using primary key by using Inline Conditions if the primary key is a number. When working with strings, extra care needs to be taken to avoid SQL Injection; check out Security section for details.

  1. db.First(&user, 10)
  2. // SELECT * FROM users WHERE id = 10;
  4. db.First(&user, "10")
  5. // SELECT * FROM users WHERE id = 10;
  7. db.Find(&users, []int{1,2,3})
  8. // SELECT * FROM users WHERE id IN (1,2,3);

If the primary key is a string (for example, like a uuid), the query will be written as follows:

  1. db.First(&user, "id = ?", "1b74413f-f3b8-409f-ac47-e8c062e3472a")
  2. // SELECT * FROM users WHERE id = "1b74413f-f3b8-409f-ac47-e8c062e3472a";

当目标对象有一个主键值时，将使用主键构建查询条件，例如：

  1. var user = User{ID: 10}
  2. db.First(&user)
  3. // SELECT * FROM users WHERE id = 10;
  5. var result User
  6. db.Model(User{ID: 10}).First(&result)
  7. // SELECT * FROM users WHERE id = 10;

NOTE: If you use gorm’s specific field types like gorm.DeletedAt, it will run a different query for retrieving object/s.

  1. type User struct {
  2.   ID           string `gorm:"primarykey;size:16"`
  3.   Name         string `gorm:"size:24"`
  4.   DeletedAt    gorm.DeletedAt `gorm:"index"`
  5. }
  7. var user = User{ID: 15}
  8. db.First(&user)
  9. //  SELECT * FROM `users` WHERE `users`.`id` = '15' AND `users`.`deleted_at` IS NULL ORDER BY `users`.`id` LIMIT 1

检索全部对象

  1. // Get all records
  2. result := db.Find(&users)
  3. // SELECT * FROM users;
  5. result.RowsAffected // returns found records count, equals `len(users)`
  6. result.Error        // returns error

条件

String 条件

  1. // Get first matched record
  2. db.Where("name = ?", "jinzhu").First(&user)
  3. // SELECT * FROM users WHERE name = 'jinzhu' ORDER BY id LIMIT 1;
  5. // Get all matched records
  6. db.Where("name <> ?", "jinzhu").Find(&users)
  7. // SELECT * FROM users WHERE name <> 'jinzhu';
  9. // IN
  10. db.Where("name IN ?", []string{"jinzhu", "jinzhu 2"}).Find(&users)
  11. // SELECT * FROM users WHERE name IN ('jinzhu','jinzhu 2');
  13. // LIKE
  14. db.Where("name LIKE ?", "%jin%").Find(&users)
  15. // SELECT * FROM users WHERE name LIKE '%jin%';
  17. // AND
  18. db.Where("name = ? AND age >= ?", "jinzhu", "22").Find(&users)
  19. // SELECT * FROM users WHERE name = 'jinzhu' AND age >= 22;
  21. // Time
  22. db.Where("updated_at > ?", lastWeek).Find(&users)
  23. // SELECT * FROM users WHERE updated_at > '2000-01-01 00:00:00';
  25. // BETWEEN
  26. db.Where("created_at BETWEEN ? AND ?", lastWeek, today).Find(&users)
  27. // SELECT * FROM users WHERE created_at BETWEEN '2000-01-01 00:00:00' AND '2000-01-08 00:00:00';

If the object’s primary key has been set, then condition query wouldn’t cover the value of primary key but use it as a ‘and’ condition. For example:

  1. var user = User{ID: 10}
  2. db.Where("id = ?", 20).First(&user)
  3. // SELECT * FROM users WHERE id = 10 and id = 20 ORDER BY id ASC LIMIT 1

This query would give record not found Error. So set the primary key attribute such as id to nil before you want to use the variable such as user to get new value from database.

Struct & Map 条件

  1. // Struct
  2. db.Where(&User{Name: "jinzhu", Age: 20}).First(&user)
  3. // SELECT * FROM users WHERE name = "jinzhu" AND age = 20 ORDER BY id LIMIT 1;
  5. // Map
  6. db.Where(map[string]interface{}{"name": "jinzhu", "age": 20}).Find(&users)
  7. // SELECT * FROM users WHERE name = "jinzhu" AND age = 20;
  9. // Slice of primary keys
  10. db.Where([]int64{20, 21, 22}).Find(&users)
  11. // SELECT * FROM users WHERE id IN (20, 21, 22);

NOTE When querying with struct, GORM will only query with non-zero fields, that means if your field’s value is 0, '', false or other zero values, it won’t be used to build query conditions, for example:

  1. db.Where(&User{Name: "jinzhu", Age: 0}).Find(&users)
  2. // SELECT * FROM users WHERE name = "jinzhu";

To include zero values in the query conditions, you can use a map, which will include all key-values as query conditions, for example:

  1. db.Where(map[string]interface{}{"Name": "jinzhu", "Age": 0}).Find(&users)
  2. // SELECT * FROM users WHERE name = "jinzhu" AND age = 0;

For more details, see Specify Struct search fields.

指定结构体查询字段

When searching with struct, you can specify which particular values from the struct to use in the query conditions by passing in the relevant field name or the dbname to Where(), for example:

  1. db.Where(&User{Name: "jinzhu"}, "name", "Age").Find(&users)
  2. // SELECT * FROM users WHERE name = "jinzhu" AND age = 0;
  4. db.Where(&User{Name: "jinzhu"}, "Age").Find(&users)
  5. // SELECT * FROM users WHERE age = 0;

内联条件

Query conditions can be inlined into methods like First and Find in a similar way to Where.

  1. // Get by primary key if it were a non-integer type
  2. db.First(&user, "id = ?", "string_primary_key")
  3. // SELECT * FROM users WHERE id = 'string_primary_key';
  5. // Plain SQL
  6. db.Find(&user, "name = ?", "jinzhu")
  7. // SELECT * FROM users WHERE name = "jinzhu";
  9. db.Find(&users, "name <> ? AND age > ?", "jinzhu", 20)
  10. // SELECT * FROM users WHERE name <> "jinzhu" AND age > 20;
  12. // Struct
  13. db.Find(&users, User{Age: 20})
  14. // SELECT * FROM users WHERE age = 20;
  16. // Map
  17. db.Find(&users, map[string]interface{}{"age": 20})
  18. // SELECT * FROM users WHERE age = 20;

Not 条件

Build NOT conditions, works similar to Where

  1. db.Not("name = ?", "jinzhu").First(&user)
  2. // SELECT * FROM users WHERE NOT name = "jinzhu" ORDER BY id LIMIT 1;
  4. // Not In
  5. db.Not(map[string]interface{}{"name": []string{"jinzhu", "jinzhu 2"}}).Find(&users)
  6. // SELECT * FROM users WHERE name NOT IN ("jinzhu", "jinzhu 2");
  8. // Struct
  9. db.Not(User{Name: "jinzhu", Age: 18}).First(&user)
  10. // SELECT * FROM users WHERE name <> "jinzhu" AND age <> 18 ORDER BY id LIMIT 1;
  12. // Not In slice of primary keys
  13. db.Not([]int64{1,2,3}).First(&user)
  14. // SELECT * FROM users WHERE id NOT IN (1,2,3) ORDER BY id LIMIT 1;

Or 条件

  1. db.Where("role = ?", "admin").Or("role = ?", "super_admin").Find(&users)
  2. // SELECT * FROM users WHERE role = 'admin' OR role = 'super_admin';
  4. // Struct
  5. db.Where("name = 'jinzhu'").Or(User{Name: "jinzhu 2", Age: 18}).Find(&users)
  6. // SELECT * FROM users WHERE name = 'jinzhu' OR (name = 'jinzhu 2' AND age = 18);
  8. // Map
  9. db.Where("name = 'jinzhu'").Or(map[string]interface{}{"name": "jinzhu 2", "age": 18}).Find(&users)
  10. // SELECT * FROM users WHERE name = 'jinzhu' OR (name = 'jinzhu 2' AND age = 18);

For more complicated SQL queries. please also refer to Group Conditions in Advanced Query.

选择特定字段

Select allows you to specify the fields that you want to retrieve from database. Otherwise, GORM will select all fields by default.

  1. db.Select("name", "age").Find(&users)
  2. // SELECT name, age FROM users;
  4. db.Select([]string{"name", "age"}).Find(&users)
  5. // SELECT name, age FROM users;
  7. db.Table("users").Select("COALESCE(age,?)", 42).Rows()
  8. // SELECT COALESCE(age,'42') FROM users;

Also check out Smart Select Fields

排序

Specify order when retrieving records from the database

  1. db.Order("age desc, name").Find(&users)
  2. // SELECT * FROM users ORDER BY age desc, name;
  4. // Multiple orders
  5. db.Order("age desc").Order("name").Find(&users)
  6. // SELECT * FROM users ORDER BY age desc, name;
  8. db.Clauses(clause.OrderBy{
  9.   Expression: clause.Expr{SQL: "FIELD(id,?)", Vars: []interface{}{[]int{1, 2, 3}}, WithoutParentheses: true},
  10. }).Find(&User{})
  11. // SELECT * FROM users ORDER BY FIELD(id,1,2,3)

Limit & Offset

Limit specify the max number of records to retrieve Offset specify the number of records to skip before starting to return the records

  1. db.Limit(3).Find(&users)
  2. // SELECT * FROM users LIMIT 3;
  4. // Cancel limit condition with -1
  5. db.Limit(10).Find(&users1).Limit(-1).Find(&users2)
  6. // SELECT * FROM users LIMIT 10; (users1)
  7. // SELECT * FROM users; (users2)
  9. db.Offset(3).Find(&users)
  10. // SELECT * FROM users OFFSET 3;
  12. db.Limit(10).Offset(5).Find(&users)
  13. // SELECT * FROM users OFFSET 5 LIMIT 10;
  15. // Cancel offset condition with -1
  16. db.Offset(10).Find(&users1).Offset(-1).Find(&users2)
  17. // SELECT * FROM users OFFSET 10; (users1)
  18. // SELECT * FROM users; (users2)

Refer to Pagination for details on how to make a paginator

Group By & Having

  1. type result struct {
  2.   Date  time.Time
  3.   Total int
  4. }
  6. db.Model(&User{}).Select("name, sum(age) as total").Where("name LIKE ?", "group%").Group("name").First(&result)
  7. // SELECT name, sum(age) as total FROM `users` WHERE name LIKE "group%" GROUP BY `name` LIMIT 1
  10. db.Model(&User{}).Select("name, sum(age) as total").Group("name").Having("name = ?", "group").Find(&result)
  11. // SELECT name, sum(age) as total FROM `users` GROUP BY `name` HAVING name = "group"
  13. rows, err := db.Table("orders").Select("date(created_at) as date, sum(amount) as total").Group("date(created_at)").Rows()
  14. defer rows.Close()
  15. for rows.Next() {
  16.   ...
  17. }
  19. rows, err := db.Table("orders").Select("date(created_at) as date, sum(amount) as total").Group("date(created_at)").Having("sum(amount) > ?", 100).Rows()
  20. defer rows.Close()
  21. for rows.Next() {
  22.   ...
  23. }
  25. type Result struct {
  26.   Date  time.Time
  27.   Total int64
  28. }
  29. db.Table("orders").Select("date(created_at) as date, sum(amount) as total").Group("date(created_at)").Having("sum(amount) > ?", 100).Scan(&results)

Distinct

Selecting distinct values from the model

  1. db.Distinct("name", "age").Order("name, age desc").Find(&results)

Distinct works with Pluck and Count too

Joins

Specify Joins conditions

  1. type result struct {
  2.   Name  string
  3.   Email string
  4. }
  6. db.Model(&User{}).Select("users.name, emails.email").Joins("left join emails on emails.user_id = users.id").Scan(&result{})
  7. // SELECT users.name, emails.email FROM `users` left join emails on emails.user_id = users.id
  9. rows, err := db.Table("users").Select("users.name, emails.email").Joins("left join emails on emails.user_id = users.id").Rows()
  10. for rows.Next() {
  11.   ...
  12. }
  14. db.Table("users").Select("users.name, emails.email").Joins("left join emails on emails.user_id = users.id").Scan(&results)
  16. // multiple joins with parameter
  17. db.Joins("JOIN emails ON emails.user_id = users.id AND emails.email = ?", "jinzhu@example.org").Joins("JOIN credit_cards ON credit_cards.user_id = users.id").Where("credit_cards.number = ?", "411111111111").Find(&user)

Joins 预加载

You can use Joins eager loading associations with a single SQL, for example:

  1. db.Joins("Company").Find(&users)
  2. // SELECT `users`.`id`,`users`.`name`,`users`.`age`,`Company`.`id` AS `Company__id`,`Company`.`name` AS `Company__name` FROM `users` LEFT JOIN `companies` AS `Company` ON `users`.`company_id` = `Company`.`id`;
  4. // inner join
  5. db.InnerJoins("Company").Find(&users)
  6. // SELECT `users`.`id`,`users`.`name`,`users`.`age`,`Company`.`id` AS `Company__id`,`Company`.`name` AS `Company__name` FROM `users` INNER JOIN `companies` AS `Company` ON `users`.`company_id` = `Company`.`id`;

Join with conditions

  1. db.Joins("Company", db.Where(&Company{Alive: true})).Find(&users)
  2. // SELECT `users`.`id`,`users`.`name`,`users`.`age`,`Company`.`id` AS `Company__id`,`Company`.`name` AS `Company__name` FROM `users` LEFT JOIN `companies` AS `Company` ON `users`.`company_id` = `Company`.`id` AND `Company`.`alive` = true;

For more details, please refer to Preloading (Eager Loading).

Joins 一个衍生表

You can also use Joins to join a derived table.

  1. type User struct {
  2.     Id  int
  3.     Age int
  4. }
  6. type Order struct {
  7.     UserId     int
  8.     FinishedAt *time.Time
  9. }
  11. query := db.Table("order").Select("MAX(order.finished_at) as latest").Joins("left join user user on order.user_id = user.id").Where("user.age > ?", 18).Group("order.user_id")
  12. db.Model(&Order{}).Joins("join (?) q on order.finished_at = q.latest", query).Scan(&results)
  13. // SELECT `order`.`user_id`,`order`.`finished_at` FROM `order` join (SELECT MAX(order.finished_at) as latest FROM `order` left join user user on order.user_id = user.id WHERE user.age > 18 GROUP BY `order`.`user_id`) q on order.finished_at = q.latest

Scan

Scanning results into a struct works similarly to the way we use Find

  1. type Result struct {
  2.   Name string
  3.   Age  int
  4. }
  6. var result Result
  7. db.Table("users").Select("name", "age").Where("name = ?", "Antonio").Scan(&result)
  9. // Raw SQL
  10. db.Raw("SELECT name, age FROM users WHERE name = ?", "Antonio").Scan(&result)