3、GROM 关联 (golang)

文章目录

• 3、GROM 关联 (golang)

• 属于

• 属于

• 外键

• 关联外键

• Belongs To 的使用

• 查询

• 查询

• Where 条件

• 普通 SQL

• Struct & Map

• Not 条件

• Or 条件

• Inline Condition 内联条件

• Extra Querying option 其它查询选项

• FirstOrInit

• Attrs

• Assign

• FirstOrCreate

• Attrs

• Assign

• Advanced Query 高级查询

• SubQuery 子查询

• 选择字段

• 排序

• 数量

• 偏移

• 总数

• Group & Having

• 连接

• Pluck

• 扫描

• Has Many

• Has Many

• 外键

• 关联外键

• 多态关联

• Has Many 的使用

• Many To Many

• Many To Many

• 互引用关联

• 多外键

• 连接表外键

• 自引用关联

• Many To Many 的使用

• 关联

• 自动创建/更新

• 跳过自动更新

• 跳过自动创建

• 跳过自动创建及更新

• 跳过引用的保存

• 关联模式

• 查找关联

• 添加关联

• 替换关联

• 删除关联

• 清空关联

• 关联的数量

• Preloading (预加载)

• 预加载

• 自动预加载

• 嵌套预加载

• 自定义预加载 SQL

属于

属于

belongs to 会与另一个模型建立一对一关系，因此声明的每一个模型实例都会”属于”另一个模型实例。

例如, 如果您的应用程序包含用户和配置文件, 并且可以将每个配置文件分配给一个用户

1type User struct {
2  gorm.Model
3  Name string
4}
5
6// `Profile` 属于 `User`， 外键是`UserID` 
7type Profile struct {
8  gorm.Model
9  UserID int
10  User   User
11  Name   string
12}

外键

Foreign Key，若要定义属于关系的外键必须存在, 默认外键使用所有者的类型名称及其主键。

对于上述例子，定义一个属于 User 的模型，外键应该是 UserID。

GORM 提供了自定义外键的方法，例如：

1type User struct {
2  gorm.Model
3  Name string
4}
5
6type Profile struct {
7  gorm.Model
8  Name      string
9  User      User `gorm:"foreignkey:UserRefer"` // 将 UserRefer 作为外键
10  UserRefer uint
11}

关联外键

对于一个 belongs to 关系，GORM 通常使用所有者的主键作为外键的值，对于上面例子，外键的值是 User 的 ID。

当你关联一个 profile 到一个 user 时，GORM 将保存 user 的 ID 到 profile 的 UserID 字段。

你可以用 association_foreignkey 标签来更改它，例如：

1type User struct {
2  gorm.Model
3  Refer string
4  Name string
5}
6
7type Profile struct {
8  gorm.Model
9  Name      string
10  User      User `gorm:"association_foreignkey:Refer"` // 将 Refer 作为关联外键
11  UserRefer string
12}

Belongs To 的使用

你可以使用 Related 查找 belongs to 关系。

1db.Model(&user).Related(&profile)
2 SELECT * FROM profiles WHERE user_id = 111; // 111 is user's ID

高级用法请参阅 关联模式

查询

查询

1// 根据主键查询第一条记录
2db.First(&user)
3 SELECT * FROM users ORDER BY id LIMIT 1;
4
5// 随机获取一条记录
6db.Take(&user)
7 SELECT * FROM users LIMIT 1;
8
9// 根据主键查询最后一条记录
10db.Last(&user)
11 SELECT * FROM users ORDER BY id DESC LIMIT 1;
12
13// 查询所有的记录
14db.Find(&users)
15 SELECT * FROM users;
16
17// 查询指定的某条记录(仅当主键为整型时可用)
18db.First(&user, 10)
19 SELECT * FROM users WHERE id = 10;

Where 条件

普通 SQL

1// 获取第一个匹配的记录
2db.Where("name = ?", "jinzhu").First(&user)
3 SELECT * FROM users WHERE name = 'jinzhu' limit 1;
4
5// 获取所有匹配的记录
6db.Where("name = ?", "jinzhu").Find(&users)
7 SELECT * FROM users WHERE name = 'jinzhu';
8
9// <>
10db.Where("name <> ?", "jinzhu").Find(&users)
11 SELECT * FROM users WHERE name <> 'jinzhu';
12
13// IN
14db.Where("name IN (?)", []string{"jinzhu", "jinzhu 2"}).Find(&users)
15 SELECT * FROM users WHERE name in ('jinzhu','jinzhu 2');
16
17// LIKE
18db.Where("name LIKE ?", "%jin%").Find(&users)
19 SELECT * FROM users WHERE name LIKE '%jin%';
20
21// AND
22db.Where("name = ? AND age >= ?", "jinzhu", "22").Find(&users)
23 SELECT * FROM users WHERE name = 'jinzhu' AND age >= 22;
24
25// Time
26db.Where("updated_at > ?", lastWeek).Find(&users)
27 SELECT * FROM users WHERE updated_at > '2000-01-01 00:00:00';
28
29// BETWEEN
30db.Where("created_at BETWEEN ? AND ?", lastWeek, today).Find(&users)
31 SELECT * FROM users WHERE created_at BETWEEN '2000-01-01 00:00:00' AND '2000-01-08 00:00:00';

Struct & Map

1// Struct
2db.Where(&User{Name: "jinzhu", Age: 20}).First(&user)
3 SELECT * FROM users WHERE name = "jinzhu" AND age = 20 ORDER BY id LIMIT 1;
4
5// Map
6db.Where(map[string]interface{}{"name": "jinzhu", "age": 20}).Find(&users)
7 SELECT * FROM users WHERE name = "jinzhu" AND age = 20;
8
9// 主键切片
10db.Where([]int64{20, 21, 22}).Find(&users)
11 SELECT * FROM users WHERE id IN (20, 21, 22);

提示 当通过结构体进行查询时，GORM将会只通过非零值字段查询，这意味着如果你的字段值为0，''， false 或者其他 零值时，将不会被用于构建查询条件，例如：

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

你可以使用指针或实现 Scanner/Valuer 接口来避免这个问题.

1// 使用指针
2type User struct {
3  gorm.Model
4  Name string
5  Age  *int
6}
7
8// 使用 Scanner/Valuer
9type User struct {
10  gorm.Model
11  Name string
12  Age  sql.NullInt64  // sql.NullInt64 实现了 Scanner/Valuer 接口
13}

Not 条件

作用与 Where 类似

1db.Not("name", "jinzhu").First(&user)
2 SELECT * FROM users WHERE name <> "jinzhu" ORDER BY id LIMIT 1;
3
4// Not In
5db.Not("name", []string{"jinzhu", "jinzhu 2"}).Find(&users)
6 SELECT * FROM users WHERE name NOT IN ("jinzhu", "jinzhu 2");
7
8// 不在主键切片中
9db.Not([]int64{1,2,3}).First(&user)
10 SELECT * FROM users WHERE id NOT IN (1,2,3) ORDER BY id LIMIT 1;
11
12db.Not([]int64{}).First(&user)
13 SELECT * FROM users ORDER BY id LIMIT 1;
14
15// 普通 SQL
16db.Not("name = ?", "jinzhu").First(&user)
17 SELECT * FROM users WHERE NOT(name = "jinzhu") ORDER BY id LIMIT 1;
18
19// Struct
20db.Not(User{Name: "jinzhu"}).First(&user)
21 SELECT * FROM users WHERE name <> "jinzhu" ORDER BY id LIMIT 1;

Or 条件

1db.Where("role = ?", "admin").Or("role = ?", "super_admin").Find(&users)
2 SELECT * FROM users WHERE role = 'admin' OR role = 'super_admin';
3
4// Struct
5db.Where("name = 'jinzhu'").Or(User{Name: "jinzhu 2"}).Find(&users)
6 SELECT * FROM users WHERE name = 'jinzhu' OR name = 'jinzhu 2';
7
8// Map
9db.Where("name = 'jinzhu'").Or(map[string]interface{}{"name": "jinzhu 2"}).Find(&users)
10 SELECT * FROM users WHERE name = 'jinzhu' OR name = 'jinzhu 2';

Inline Condition 内联条件

作用与 Where 类似

当内联条件与 多个立即执行方法 一起使用时, 内联条件不会传递给后面的立即执行方法。

1// 通过主键获取 (只适用于整数主键)
2db.First(&user, 23)
3 SELECT * FROM users WHERE id = 23;
4// 如果是一个非整数类型，则通过主键获取
5db.First(&user, "id = ?", "string_primary_key")
6 SELECT * FROM users WHERE id = 'string_primary_key';
7
8// Plain SQL
9db.Find(&user, "name = ?", "jinzhu")
10 SELECT * FROM users WHERE name = "jinzhu";
11
12db.Find(&users, "name <> ? AND age > ?", "jinzhu", 20)
13 SELECT * FROM users WHERE name <> "jinzhu" AND age > 20;
14
15// Struct
16db.Find(&users, User{Age: 20})
17 SELECT * FROM users WHERE age = 20;
18
19// Map
20db.Find(&users, map[string]interface{}{"age": 20})
21 SELECT * FROM users WHERE age = 20;

Extra Querying option 其它查询选项

1// 为查询 SQL 添加额外的 SQL 操作
2db.Set("gorm:query_option", "FOR UPDATE").First(&user, 10)
3 SELECT * FROM users WHERE id = 10 FOR UPDATE;

FirstOrInit

获取匹配的第一条记录，否则根据给定的条件初始化一个新的对象 (仅支持 struct 和 map 条件)

1// 未找到
2db.FirstOrInit(&user, User{Name: "non_existing"})
3 user -> User{Name: "non_existing"}
4
5// 找到
6db.Where(User{Name: "Jinzhu"}).FirstOrInit(&user)
7 user -> User{Id: 111, Name: "Jinzhu", Age: 20}
8db.FirstOrInit(&user, map[string]interface{}{"name": "jinzhu"})
9 user -> User{Id: 111, Name: "Jinzhu", Age: 20}

Attrs

如果记录未找到，将使用参数初始化 struct.

1// 未找到
2db.Where(User{Name: "non_existing"}).Attrs(User{Age: 20}).FirstOrInit(&user)
3 SELECT * FROM USERS WHERE name = 'non_existing' ORDER BY id LIMIT 1;
4 user -> User{Name: "non_existing", Age: 20}
5
6db.Where(User{Name: "non_existing"}).Attrs("age", 20).FirstOrInit(&user)
7 SELECT * FROM USERS WHERE name = 'non_existing' ORDER BY id LIMIT 1;
8 user -> User{Name: "non_existing", Age: 20}
9
10// 找到
11db.Where(User{Name: "Jinzhu"}).Attrs(User{Age: 30}).FirstOrInit(&user)
12 SELECT * FROM USERS WHERE name = jinzhu' ORDER BY id LIMIT 1;
13 user -> User{Id: 111, Name: "Jinzhu", Age: 20}

Assign

不管记录是否找到，都将参数赋值给 struct.

1// 未找到
2db.Where(User{Name: "non_existing"}).Assign(User{Age: 20}).FirstOrInit(&user)
3 user -> User{Name: "non_existing", Age: 20}
4
5// 找到
6db.Where(User{Name: "Jinzhu"}).Assign(User{Age: 30}).FirstOrInit(&user)
7 SELECT * FROM USERS WHERE name = jinzhu' ORDER BY id LIMIT 1;
8 user -> User{Id: 111, Name: "Jinzhu", Age: 30}

FirstOrCreate

获取匹配的第一条记录, 否则根据给定的条件创建一个新的记录 (仅支持 struct 和 map 条件)

1// 未找到
2db.FirstOrCreate(&user, User{Name: "non_existing"})
3 INSERT INTO "users" (name) VALUES ("non_existing");
4 user -> User{Id: 112, Name: "non_existing"}
5
6// 找到
7db.Where(User{Name: "Jinzhu"}).FirstOrCreate(&user)
8 user -> User{Id: 111, Name: "Jinzhu"}

Attrs

如果记录未找到，将使用参数创建 struct 和记录.

1// 未找到
2db.Where(User{Name: "non_existing"}).Attrs(User{Age: 20}).FirstOrCreate(&user)
3 SELECT * FROM users WHERE name = 'non_existing' ORDER BY id LIMIT 1;
4 INSERT INTO "users" (name, age) VALUES ("non_existing", 20);
5 user -> User{Id: 112, Name: "non_existing", Age: 20}
6
7// 找到
8db.Where(User{Name: "jinzhu"}).Attrs(User{Age: 30}).FirstOrCreate(&user)
9 SELECT * FROM users WHERE name = 'jinzhu' ORDER BY id LIMIT 1;
10 user -> User{Id: 111, Name: "jinzhu", Age: 20}

Assign

不管记录是否找到，都将参数赋值给 struct 并保存至数据库.

1// 未找到
2db.Where(User{Name: "non_existing"}).Assign(User{Age: 20}).FirstOrCreate(&user)
3 SELECT * FROM users WHERE name = 'non_existing' ORDER BY id LIMIT 1;
4 INSERT INTO "users" (name, age) VALUES ("non_existing", 20);
5 user -> User{Id: 112, Name: "non_existing", Age: 20}
6
7// 找到
8db.Where(User{Name: "jinzhu"}).Assign(User{Age: 30}).FirstOrCreate(&user)
9 SELECT * FROM users WHERE name = 'jinzhu' ORDER BY id LIMIT 1;
10 UPDATE users SET age=30 WHERE id = 111;
11 user -> User{Id: 111, Name: "jinzhu", Age: 30}

Advanced Query 高级查询

SubQuery 子查询

基于 *gorm.expr 的子查询

1db.Where("amount > ?", db.Table("orders").Select("AVG(amount)").Where("state = ?", "paid").SubQuery()).Find(&orders)
2// SELECT * FROM "orders"  WHERE "orders"."deleted_at" IS NULL AND (amount > (SELECT AVG(amount) FROM "orders"  WHERE (state = 'paid')));

选择字段

Select，指定你想从数据库中检索出的字段，默认会选择全部字段。

1db.Select("name, age").Find(&users)
2 SELECT name, age FROM users;
3
4db.Select([]string{"name", "age"}).Find(&users)
5 SELECT name, age FROM users;
6
7db.Table("users").Select("COALESCE(age,?)", 42).Rows()
8 SELECT COALESCE(age,'42') FROM users;

排序

Order，指定从数据库中检索出记录的顺序。设置第二个参数 reorder 为 true ，可以覆盖前面定义的排序条件。

1db.Order("age desc, name").Find(&users)
2 SELECT * FROM users ORDER BY age desc, name;
3
4// 多字段排序
5db.Order("age desc").Order("name").Find(&users)
6 SELECT * FROM users ORDER BY age desc, name;
7
8// 覆盖排序
9db.Order("age desc").Find(&users1).Order("age", true).Find(&users2)
10 SELECT * FROM users ORDER BY age desc; (users1)
11 SELECT * FROM users ORDER BY age; (users2)

数量

Limit，指定从数据库检索出的最大记录数。

1db.Limit(3).Find(&users)
2 SELECT * FROM users LIMIT 3;
3
4// -1 取消 Limit 条件
5db.Limit(10).Find(&users1).Limit(-1).Find(&users2)
6 SELECT * FROM users LIMIT 10; (users1)
7 SELECT * FROM users; (users2)

偏移

Offset，指定开始返回记录前要跳过的记录数。

1db.Offset(3).Find(&users)
2 SELECT * FROM users OFFSET 3;
3
4// -1 取消 Offset 条件
5db.Offset(10).Find(&users1).Offset(-1).Find(&users2)
6 SELECT * FROM users OFFSET 10; (users1)
7 SELECT * FROM users; (users2)

总数

Count，该 model 能获取的记录总数。

1db.Where("name = ?", "jinzhu").Or("name = ?", "jinzhu 2").Find(&users).Count(&count)
2 SELECT * from USERS WHERE name = 'jinzhu' OR name = 'jinzhu 2'; (users)
3 SELECT count(*) FROM users WHERE name = 'jinzhu' OR name = 'jinzhu 2'; (count)
4
5db.Model(&User{}).Where("name = ?", "jinzhu").Count(&count)
6 SELECT count(*) FROM users WHERE name = 'jinzhu'; (count)
7
8db.Table("deleted_users").Count(&count)
9 SELECT count(*) FROM deleted_users;
10
11db.Table("deleted_users").Select("count(distinct(name))").Count(&count)
12 SELECT count( distinct(name) ) FROM deleted_users; (count)

注意 Count 必须是链式查询的最后一个操作 ，因为它会覆盖前面的 SELECT，但如果里面使用了 count 时不会覆盖

Group & Having

1rows, err := db.Table("orders").Select("date(created_at) as date, sum(amount) as total").Group("date(created_at)").Rows()
2for rows.Next() {
3  ...
4}
5
6rows, err := db.Table("orders").Select("date(created_at) as date, sum(amount) as total").Group("date(created_at)").Having("sum(amount) > ?", 100).Rows()
7for rows.Next() {
8  ...
9}
10
11type Result struct {
12  Date  time.Time
13  Total int64
14}
15db.Table("orders").Select("date(created_at) as date, sum(amount) as total").Group("date(created_at)").Having("sum(amount) > ?", 100).Scan(&results)

连接

Joins，指定连接条件

1rows, err := db.Table("users").Select("users.name, emails.email").Joins("left join emails on emails.user_id = users.id").Rows()
2for rows.Next() {
3  ...
4}
5
6db.Table("users").Select("users.name, emails.email").Joins("left join emails on emails.user_id = users.id").Scan(&results)
7
8// 多连接及参数
9db.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)

Pluck

Pluck，查询 model 中的一个列作为切片，如果您想要查询多个列，您应该使用 Scan

1var ages []int64
2db.Find(&users).Pluck("age", &ages)
3
4var names []string
5db.Model(&User{}).Pluck("name", &names)
6
7db.Table("deleted_users").Pluck("name", &names)
8
9// 想查询多个字段？ 这样做：
10db.Select("name, age").Find(&users)

扫描

Scan，扫描结果至一个 struct.

1type Result struct {
2  Name string
3  Age  int
4}
5
6var result Result
7db.Table("users").Select("name, age").Where("name = ?", "Antonio").Scan(&result)
8
9// 原生 SQL
10db.Raw("SELECT name, age FROM users WHERE name = ?", "Antonio").Scan(&result)

Has Many

Has Many

在一个 has many 关联中，其也与另一个 model 建立了一对多关系，不同于 has one，model 的拥有者可以有零个或多个实例。

例如，你的应用包含了用户和信用卡，并且每个用户可以有多张信用卡。

1// User 可以有多张信用卡(CreditCards), UserID 是外键
2type User struct {
3  gorm.Model
4  CreditCards []CreditCard
5}
6
7type CreditCard struct {
8  gorm.Model
9  Number   string
10  UserID  uint
11}

外键

Foreign Key，在 has many 关系中，被拥有 model 必须存在一个外键字段，默认的外键字段名称通常使用其拥有者 model 加上它的主键（比如 UserID, CardID, 等）。

例如：定义一个属于 User 的 model，它的外键应该为 UserID.

要使用另一个字段作为外键，你可以通过标签 foreignkey 来定制它，例如：

1type User struct {
2  gorm.Model
3  CreditCards []CreditCard `gorm:"foreignkey:UserRefer"`
4}
5
6type CreditCard struct {
7  gorm.Model
8  Number    string
9  UserRefer uint
10}

关联外键

Association ForeignKey，GORM 通常使用拥有者的主键作为外键的值，在上面的例子中，它是 User 的 ID.

当你为用户关联信用卡时，GORM 会保存用户的 ID 到信用卡的 UserID 字段。

您可以通过标签 association_foreignkey 来改变它，例如：

1type User struct {
2  gorm.Model
3  MemberNumber string
4  CreditCards  []CreditCard `gorm:"foreignkey:UserMemberNumber;association_foreignkey:MemberNumber"`
5}
6
7type CreditCard struct {
8  gorm.Model
9  Number           string
10  UserMemberNumber string
11}

多态关联

Polymorphism Association，GORM 支持 has many 和 has one 的多态关联。

1type Cat struct {
2  ID    int
3  Name  string
4  Toy   []Toy `gorm:"polymorphic:Owner;"`
5}
6
7type Dog struct {
8  ID   int
9  Name string
10  Toy  []Toy `gorm:"polymorphic:Owner;"`
11}
12
13type Toy struct {
14  ID        int
15  Name      string
16  OwnerID   int
17  OwnerType string
18}

注意：many-to-many 明确的不支持多态关联，如果使用会抛出错误。

Has Many 的使用

你可以通过 Related 使用 has many 关联。

1db.Model(&user).Related(&emails)
2 SELECT * FROM emails WHERE user_id = 111; // 111 是 user 的主键

高级用法请参阅 关联模式

Many To Many

Many To Many

Many to Many 在两个 model 中添加一张连接表。

比如说，你的应用包含 User 和 Language，一个 User 可以说多种 Language，多个 User 也可以说一种 Language。

1// User 拥有并属于多种 Language，使用 `user_languages` 连接表
2type User struct {
3  gorm.Model
4  Languages         []Language `gorm:"many2many:user_languages;"`
5}
6
7type Language struct {
8  gorm.Model
9  Name string
10}

互引用关联

1// User 拥有并属于多种 Language，使用 `user_languages` 连接表
2type User struct {
3  gorm.Model
4  Languages         []*Language `gorm:"many2many:user_languages;"`
5}
6
7type Language struct {
8  gorm.Model
9  Name string
10  Users               []*User     `gorm:"many2many:user_languages;"`
11}
12
13var users []User
14language := Language{}
15
16db.First(&language, "id = ?", 111)
17
18db.Model(&language).Related(&users,  "Users")
19 SELECT * FROM "users" INNER JOIN "user_languages" ON "user_languages"."user_id" = "users"."id" WHERE  ("user_languages"."language_id" IN ('111'))

多外键

1type CustomizePerson struct {
2  IdPerson string             `gorm:"primary_key:true"`
3  Accounts []CustomizeAccount `gorm:"many2many:PersonAccount;association_foreignkey:idAccount;foreignkey:idPerson"`
4}
5
6type CustomizeAccount struct {
7  IdAccount string `gorm:"primary_key:true"`
8  Name      string
9}

Foreign Keys，它将为这两个 struct 创建多对多关系，并且他们的关系将被保存到连接表 PersonAccount ，连接表的外键为 customize_person_id_person 和 customize_account_id_account.

连接表外键

Jointable ForeignKey，如果你想改变连接表的外键，你可以使用标签 association_jointable_foreignkey 和 jointable_foreignkey.

1type CustomizePerson struct {
2  IdPerson string             `gorm:"primary_key:true"`
3  Accounts []CustomizeAccount `gorm:"many2many:PersonAccount;foreignkey:idPerson;association_foreignkey:idAccount;association_jointable_foreignkey:account_id;jointable_foreignkey:person_id;"`
4}
5
6type CustomizeAccount struct {
7  IdAccount string `gorm:"primary_key:true"`
8  Name      string
9}

自引用关联

Self-Referencing，在自引用的多对多关系中，你必须在连接表中修改关联外键。

使用属性名及其主键生成关联外键，使得关联外键与外键不同，比如：

1type User struct {
2  gorm.Model
3  Friends []*User `gorm:"many2many:friendships;association_jointable_foreignkey:friend_id"`
4}

GORM 会生成一个关联表，其外键为 user_id 和 friend_id，并用其保存自引用用户关系。

然后你还是可以像正常关系一样操作它们，比如：

1DB.Preload("Friends").First(&user, "id = ?", 1)
2
3DB.Model(&user).Association("Friends").Append(&User{Name: "friend1"}, &User{Name: "friend2"})
4
5DB.Model(&user).Association("Friends").Delete(&User{Name: "friend2"})
6
7DB.Model(&user).Association("Friends").Replace(&User{Name: "new friend"})
8
9DB.Model(&user).Association("Friends").Clear()
10
11DB.Model(&user).Association("Friends").Count()

Many To Many 的使用

1db.Model(&user).Related(&languages, "Languages")
2 SELECT * FROM "languages" INNER JOIN "user_languages" ON "user_languages"."language_id" = "languages"."id" WHERE "user_languages"."user_id" = 111
3
4// 查询 user 时会预加载 Languages
5db.Preload("Languages").First(&user)

高级用法请参阅 关联模式

关联

自动创建/更新

创建/更新记录时, GORM 将自动保存关联及其引用。如果关联具有主键, GORM 将调用 Update 来保存它, 否则将创建它。

1user := User{
2  Name:            "jinzhu",
3  BillingAddress:  Address{Address1: "Billing Address - Address 1"},
4  ShippingAddress: Address{Address1: "Shipping Address - Address 1"},
5  Emails:          []Email{
6    {Email: "jinzhu@example.com"},
7    {Email: "jinzhu-2@example.com"},
8  },
9  Languages:       []Language{
10    {Name: "ZH"},
11    {Name: "EN"},
12  },
13}
14
15db.Create(&user)
16 BEGIN TRANSACTION;
17 INSERT INTO "addresses" (address1) VALUES ("Billing Address - Address 1");
18 INSERT INTO "addresses" (address1) VALUES ("Shipping Address - Address 1");
19 INSERT INTO "users" (name,billing_address_id,shipping_address_id) VALUES ("jinzhu", 1, 2);
20 INSERT INTO "emails" (user_id,email) VALUES (111, "jinzhu@example.com");
21 INSERT INTO "emails" (user_id,email) VALUES (111, "jinzhu-2@example.com");
22 INSERT INTO "languages" ("name") VALUES ('ZH');
23 INSERT INTO user_languages ("user_id","language_id") VALUES (111, 1);
24 INSERT INTO "languages" ("name") VALUES ('EN');
25 INSERT INTO user_languages ("user_id","language_id") VALUES (111, 2);
26 COMMIT;
27
28db.Save(&user)

跳过自动更新

如果数据库中已存在关联, 你可能不希望对其进行更新。

可以使用 DB 设置, 将 gorm: association_autoupdate 设置为 false

1// Don't update associations having primary key, but will save reference
2db.Set("gorm:association_autoupdate", false).Create(&user)
3db.Set("gorm:association_autoupdate", false).Save(&user)

或者使用 GORM tags gorm:"association_autoupdate:false"

1type User struct {
2  gorm.Model
3  Name       string
4  CompanyID  uint
5  // Don't update associations having primary key, but will save reference
6  Company    Company `gorm:"association_autoupdate:false"`
7}

跳过自动创建

即使你禁用了 AutoUpdating，没有主键的关联仍然会被创建，所有关联的引用也会被保存。

如果你也想跳过，那么你可以通过 DB 的设置，将gorm:association_autocreate设置为false

1// Don't create associations w/o primary key, WON'T save its reference
2db.Set("gorm:association_autocreate", false).Create(&user)
3db.Set("gorm:association_autocreate", false).Save(&user)

或使用 GORM tags GORM: "association_autocreate: false"

1type User struct {
2  gorm.Model
3  Name       string
4  // Don't create associations w/o primary key, WON'T save its reference
5  Company1   Company `gorm:"association_autocreate:false"`
6}

跳过自动创建及更新

若要禁用 自动创建 及 自动更新, 可以将这两个设置一起使用

1db.Set("gorm:association_autoupdate", false).Set("gorm:association_autocreate", false).Create(&user)
2
3type User struct {
4  gorm.Model
5  Name    string
6  Company Company `gorm:"association_autoupdate:false;association_autocreate:false"`
7}

或使用 GORM Tag gorm: save_associations

1db.Set("gorm:save_associations", false).Create(&user)
2db.Set("gorm:save_associations", false).Save(&user)
3
4type User struct {
5  gorm.Model
6  Name    string
7  Company Company `gorm:"save_associations:false:false"`
8}

跳过引用的保存

如果你不想保存关联的引用，那么你可以使用下面的技巧

1db.Set("gorm:association_save_reference", false).Save(&user)
2db.Set("gorm:association_save_reference", false).Create(&user)

或者使用 GORM Tag

1type User struct {
2  gorm.Model
3  Name       string
4  CompanyID  uint
5  Company    Company `gorm:"association_save_reference:false"`
6}

关联模式

关联模式包含几个帮助方法，可以更方便的来管理关联

1// 开始使用关联模式
2var user User
3db.Model(&user).Association("Languages")
4// `user` 是源，必须包含主键
5// `Languages` 是关系中的源的字段名
6// 只有在满足上面两个条件时，关联模式才能正常工作，请注意检查错误：
7// db.Model(&user).Association("Languages").Error

查找关联

查找匹配的关联

db.Model(&user).Association("Languages").Find(&languages)

添加关联

为many to many，has many添加新的关联关系代替当前的关联关系has one，belongs to

1db.Model(&user).Association("Languages").Append([]Language{languageZH, languageEN})
2db.Model(&user).Association("Languages").Append(Language{Name: "DE"})

替换关联

使用新关联替换当前关联

1db.Model(&user).Association("Languages").Replace([]Language{languageZH, languageEN})
2db.Model(&user).Association("Languages").Replace(Language{Name: "DE"}, languageEN)

删除关联

删除关联的引用，不会删除关联本身

1db.Model(&user).Association("Languages").Delete([]Language{languageZH, languageEN})
2db.Model(&user).Association("Languages").Delete(languageZH, languageEN)

清空关联

清空对关联的引用，不会删除关联本身

db.Model(&user).Association("Languages").Clear()

关联的数量

返回关联的数量

db.Model(&user).Association("Languages").Count()

Preloading (预加载)

预加载

1// 下面的例子会用到 User 和 Order 结构体
2type User struct {
3  gorm.Model
4  Username string
5  Orders Order
6}
7type Order struct {
8  gorm.Model
9  UserID uint
10  Price float64
11}
12// Preload 方法的参数应该是主结构体的字段名
13db.Preload("Orders").Find(&users)
14 SELECT * FROM users;
15 SELECT * FROM orders WHERE user_id IN (1,2,3,4);
16
17db.Preload("Orders", "state NOT IN (?)", "cancelled").Find(&users)
18 SELECT * FROM users;
19 SELECT * FROM orders WHERE user_id IN (1,2,3,4) AND state NOT IN ('cancelled');
20
21db.Where("state = ?", "active").Preload("Orders", "state NOT IN (?)", "cancelled").Find(&users)
22 SELECT * FROM users WHERE state = 'active';
23 SELECT * FROM orders WHERE user_id IN (1,2) AND state NOT IN ('cancelled');
24
25db.Preload("Orders").Preload("Profile").Preload("Role").Find(&users)
26 SELECT * FROM users;
27 SELECT * FROM orders WHERE user_id IN (1,2,3,4); // has many
28 SELECT * FROM profiles WHERE user_id IN (1,2,3,4); // has one
29 SELECT * FROM roles WHERE id IN (4,5,6); // belongs to

自动预加载

Gorm 默认总是会自动预加载关联记录

1type User struct {
2  gorm.Model
3  Name       string
4  CompanyID  uint
5  Company    Company `gorm:"PRELOAD:false"` // 不会预加载
6  Role       Role                           // 预加载
7}
8
9db.Set("gorm:auto_preload", true).Find(&users)

嵌套预加载

1db.Preload("Orders.OrderItems").Find(&users)
2db.Preload("Orders", "state = ?", "paid").Preload("Orders.OrderItems").Find(&users)

自定义预加载 SQL

你可以通过传入 func(db *gorm.DB) *gorm.DB 来自定义预加载，比如：

1db.Preload("Orders", func(db *gorm.DB) *gorm.DB {
2  return db.Order("orders.amount DESC")
3}).Find(&users)
4 SELECT * FROM users;
5 SELECT * FROM orders WHERE user_id IN (1,2,3,4) order by orders.amount DESC;