Has-One vs Belongs-To

Both regards 1:1 (one to one) relations, but implies different behaviour

Sample models

A user can have 1 calender, and 1 calender can only be used by 1 user. Using Go as sample language, and behaviour may be specific to GORM.

type User struct {
    ID        uint
    FirstName string
    LastName  string
}

type Calender struct {
    ID   uint
    Name string
}

Has-One

The subject model is the owner.

If User has one Calender, then the User is the owner of the Calender.

type User struct {
    ID        uint
    FirstName string
    LastName  string
    Calender  Calender // <--
}

type Calender struct {
    ID     uint
    Name   string
    UserID uint // <--
}

Implies:

  • if User is deleted, then so is Calender.
  • if Calender is deleted, then User could stick around.

Belongs-To

The subject model is the target.

If User belongs to Calender, then the Calender is the owner of the User.

type User struct {
    ID          uint
    FirstName   string
    LastName    string
    Calender    Calender // <--
    CalenderID  uint     // <--
}

type Calender struct {
    ID     uint
    Name   string
}

Implies:

  • if Calender is deleted, then so is User.
  • if User is deleted, then Calender could stick around.

References

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