How to delete related models of a relation in Gorm?

When developing with GORM, managing relationships between models and executing deletion operations is a common requirement. To delete related models in GORM, it primarily depends on your specific needs: for instance, whether you want to delete the association itself (by removing records from the join table) or delete the instances of the associated models simultaneously. The following outlines common scenarios and their respective handling methods:

1. Deleting the Association Itself (e.g., Many-to-Many Relationship)

Suppose there are two models User and Language, which have a many-to-many relationship.

go
type User struct {
    gorm.Model
    Languages []Language `gorm:"many2many:user_languages;"`
}


type Language struct {
    gorm.Model
    Name string
}

If you only want to delete the association between a user and a language without deleting the language record itself, use the following code:

go
db.Model(&user).Association("Languages").Delete(&language)

Here, user is an instance of User, and language is an instance of Language to be removed from the user's language list. This operation only removes the corresponding records from the join table user_languages.

2. Deleting Instances of Associated Models

If you want to delete a user and all associated languages (assuming these languages belong exclusively to this user), you can implement GORM's delete hook or manually delete these relationships using a transaction.

Using DELETE Hook

Set up a DELETE hook for the User model to trigger when the user is deleted:

go
func (u *User) BeforeDelete(tx *gorm.DB) (err error) {
    // Delete all associated languages
    tx.Where("user_id = ?", u.ID).Delete(&Language{})
    return
}

Then, when deleting the user:

go
db.Delete(&user)

This will automatically delete all languages associated with the user.

Using Transaction for Manual Deletion

go
err := db.Transaction(func(tx *gorm.DB) error {
    // First delete associated languages
    if err := tx.Where("user_id = ?", user.ID).Delete(&Language{}).Error; err != nil {
        return err
    }

    // Then delete the user itself
    if err := tx.Delete(&user).Error; err != nil {
        return err
    }

    return nil
})
if err != nil {
    log.Println("Deletion failed:", err)
}

Here, we ensure both the user and its associated languages are deleted successfully through a transaction, maintaining data consistency.

The above represent the two primary approaches for handling related model deletions in GORM. Selecting the appropriate method depends on your specific application requirements and data model design.