2.6 KiB
Has One Has One A has one association sets up a one-to-one connection with another model, but with somewhat different semantics (and consequences). This association indicates that each instance of a model contains or possesses one instance of another model.
For example, if your application includes users and credit cards, and each user can only have one credit card.
Declare // User has one CreditCard, UserID is the foreign key type User struct { gorm.Model CreditCard CreditCard }
type CreditCard struct { gorm.Model Number string UserID uint } Retrieve // Retrieve user list with eager loading credit card func GetAll(db *gorm.DB) ([]User, error) { var users []User err := db.Model(&User{}).Preload("CreditCard").Find(&users).Error return users, err } Override Foreign Key For a has one relationship, a foreign key field must also exist, the owner will save the primary key of the model belongs to it into this field.
The field’s name is usually generated with has one model’s type plus its primary key, for the above example it is UserID.
When you give a credit card to the user, it will save the User’s ID into its UserID field.
If you want to use another field to save the relationship, you can change it with tag foreignKey, e.g:
type User struct {
gorm.Model
CreditCard CreditCard gorm:"foreignKey:UserName"
// use UserName as foreign key
}
type CreditCard struct { gorm.Model Number string UserName string } Override References By default, the owned entity will save the has one model’s primary key into a foreign key, you could change to save another field’s value, like using Name for the below example.
You are able to change it with tag references, e.g:
type User struct {
gorm.Model
Name string gorm:"index"
CreditCard CreditCard gorm:"foreignKey:UserName;references:Name"
}
type CreditCard struct { gorm.Model Number string UserName string } CRUD with Has One Please checkout Association Mode for working with has one relations
Eager Loading GORM allows eager loading has one associations with Preload or Joins, refer Preloading (Eager loading) for details
Self-Referential Has One type User struct { gorm.Model Name string ManagerID *uint Manager *User } FOREIGN KEY Constraints You can setup OnUpdate, OnDelete constraints with tag constraint, it will be created when migrating with GORM, for example:
type User struct {
gorm.Model
CreditCard CreditCard gorm:"constraint:OnUpdate:CASCADE,OnDelete:SET NULL;"
}
type CreditCard struct { gorm.Model Number string UserID uint } You are also allowed to delete selected has one associations with Select when deleting, checkout Delete with Select for details