[Gorm] model relationship -hasone

One 、 summary

• HasOne Establish a one-to-one relationship with another model , This association indicates that each instance of a model contains or owns another model instance .

Two 、 model

• Realization HasOne Model , The owner needs to define the model variables of the owner （ Associate model variables ）, And specify ：

  (1) Foreign keys ： stay Owner Defined in the model , Mark in the associated model variable . The default is Owner model name ID, It needs to be explicitly defined in the association model .

  (2) quote ： stay The owner Defined in the model , The type should be the same as that of the foreign key variable The same type , Mark in the associated model variable , The default is the primary key of the associated model .

• To the user User Have CreditCard For example , The model is defined as follows ：

  (1) CreditCard Associate model variables , Foreign key defaults to CreditCard Model UserID, Referenced as User Model ID.

  //  Owner model .
  type User struct {
        
     ID         uint `gorm:"primary_key"`  //  Default reference 
     Password   string     `gorm:"->:false;<-"`
     CreditCard CreditCard  //  Associate model variables .
  }
  
  //  Association model .
  type CreditCard struct {
        
     ID       uint   `gorm:"primary_key"`
     UserID 	uint  //  Default foreign key , You need to explicitly define .
     Number   string `gorm:"type:varchar(20)"`
  }
  

  (2) After building the table , stay CredictCard In the table , A new field will be added user_id, It means that we should CreditCard Record the information associated with it User Primary key .

  • User Table field description

• CreditCard Table field description

3、 ... and 、 redefinition

1. Redefine foreign keys

• Redefine foreign keys , That is, the fields that point to references in the association model , It needs to be marked in the associated model variables .
• Redefine as follows UserRefer For foreign key , Use foreignKey Annotate associated model variables CreditCard.

type User struct {
    
	ID         uint `gorm:"primary_key"`
	Name       string
	Password   string     `gorm:"->:false;<-"`
	CreditCard CreditCard `gorm:"foreignKey:UserRefer"`
}

type CreditCard struct {
    
	ID        uint `gorm:"primary_key"`
	UserRefer uint
	Number    string `gorm:"type:varchar(20)"`
}

2. Redefine reference

• Redefine reference , That is, the identifier pointed by the foreign key , It needs to be marked in the associated model variables .
• Redefine as follows Name Citing .

type User struct {
    
   ID         uint `gorm:"primary_key"`
   Name       string
   Password   string     `gorm:"->:false;<-"`
   CreditCard CreditCard `gorm:"foreignKey:UserName;references:Name"`
}

type CreditCard struct {
    
   ID       uint `gorm:"primary_key"`
   UserName string
   Number   string `gorm:"type:varchar(20)"`
}

Four 、 The relevant operation

• The following operations are based on HasOne Association model

type User struct {
    
   ID         uint `gorm:"primary_key"`
   Name       string
   Password   string     `gorm:"->:false;<-"`
   CreditCard CreditCard `gorm:"foreignKey:UserName;references:Name"`
}

type CreditCard struct {
    
   ID       uint `gorm:"primary_key"`
   UserName string
   Number   string `gorm:"type:varchar(20)"`
}

1. preservation

• Declare the complete structure variable , call Save Method to save .

func TestSaveUser() {
    
   user := User{
    
      Name:     "Jason",
      Password: "12345",
      CreditCard: CreditCard{
    
         Number: "1234567890",
      },
   }
   err := SaveUser(user)
   if err != nil {
    
      log.Println(" User save failed !")
   } else {
    
      log.Println(" User saved successfully ！")
   }
}

func SaveUser(user User) error {
    
   err := db.Save(&user).Error
   return err
}

2. Delete

• There are two strategies for deleting instances ：

​ (1) together with HasOne The associated object record is deleted , After deleting the user as above, delete it together with the account record . use Select Method . as follows , Use Select Method to select the associated model , Delete together with the model record .

func DeleteUserByName(name string) error {
    
   var user User
   var err error
   db.Model(&user).Where("name = ?", name).First(&user)
   err = db.Model(&user).Select("CreditCard").Delete(&user).Error
   return err
}

​ (2) Do not delete the associated model record , And (1) type , Don't use Select Method .

3. Inquire about

• When querying, you need Load the associated model , Use Preload Method loading .

  func GetUserByName(name string) (User, error) {
        
     var user User
     err := db.Model(&user).Preload("CreditCard").Where("name = ?", name).First(&user).Error
     return user, err
  }