How to Define and Use Foreign Key Constraints in GORM?

How to define and use a foreign key constraint in GORM?

In the realm of database design, foreign keys play a crucial role in establishing relationships and maintaining data integrity. For GORM users, understanding how to define and use foreign key constraints is essential.

Understanding the Problem

Consider the scenario described in the question, where we have two models: User and UserInfo. We need to establish a foreign key relationship between the UID field in UserInfo and the id field in User.

GORM's Foreign Key Generation

In GORM versions prior to 2.0, we needed to manually define foreign key constraints using the AddForeignKey method. In GORM 2.0 and later, this step is no longer necessary.

// GORM version 1.x
db.Model(&models.UserInfo{}).AddForeignKey("u_id", "t_user(id)", "RESTRICT", "RESTRICT")

Automated Foreign Key Definition

However, for older versions of GORM, we can still define foreign keys as shown below.

type User struct {
    DBBase
    Email    string `gorm:"column:email" json:"email"`
    Password string `gorm:"column:password" json:"-"`
}

func (User) TableName() string {
    return "t_user"
}

type UserInfo struct {
    User      User   `gorm:"foreignkey:u_id;association_foreignkey:id"`
    UID       uint   `gorm:"column:u_id" json:"-"`
    FirstName string `gorm:"column:first_name" json:"first_name"`
    LastName  string `gorm:"column:last_name" json:"last_name"`
    Phone     string `gorm:"column:phone" json:"phone"`
    Address   string `gorm:"column:address" json:"address"`
}

func (UserInfo) TableName() string {
    return "t_user_info"
}

Note that in this example, we define the foreign key relationship menggunakan the gorm:"foreignkey:..." and gorm:"association_foreignkey:..." annotations.

Setting Foreign Key Values in Code

Next, let's address the issue of setting foreign key values correctly. In the provided code:

func (dao *AuthDAO) Register(rs app.RequestScope, user *models.User, userInfo *models.UserInfo) (userErr error, userInfoErr error) {
    createUser := rs.Db().Create(&user)
    userInfo.UID = user.ID
    createUserInfo := rs.Db().Create(&userInfo)

    return createUser.Error, createUserInfo.Error
}

We set userInfo.UID to user.ID after creating the User instance. This approach is valid and will correctly establish the foreign key relationship.

In conclusion, understanding foreign key relationships and their implementation in GORM is crucial for maintaining data integrity in database-driven applications. By following the suggested solutions and annotations, you can effectively define and utilize foreign key constraints in your GORM models.

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