Define a Self-Referential Many-to-Many Model in GORM

stack:

• Language: Go
• ORM: GORM

ref:

• custom join table
• self referential table
• custom foreign key on join table

case:

• Self-referential table
• Association type: many-to-many
• Join table has additional columns beyond the two foreign keys

step:

1. Define Item

type Item struct {
    ID         string `gorm:"primaryKey; type:VARCHAR(36); NOT NULL"`
    Name       string `gorm:"type:VARCHAR(100); NOT NULL"`
    Price      int32  `gorm:"type:INT; NOT NULL"`
    ChildItems []Item `gorm:"many2many:parent_child_items;foreignKey:ID;joinForeignKey:ParentID;References:ID;joinReferences:ChildID"`
}

Which creates join table: parent_child_items

• foreign key: parent_id, reference: items.id
• foreign key: client_id, reference: items.id

1. Define ParentChildItem

type ParentChildItem struct {
    ParentID string `gorm:"primaryKey; type:VARCHAR(36); NOT NULL"`
    ChildID  string `gorm:"primaryKey; type:VARCHAR(36); NOT NULL"`
    CreatedAt time.Time
    DeletedAt gorm.DeletedAt
}

We define this because the parent_child_items table stores more than just parent_id and child_id. It’s a custom association table with extra fields (CreatedAt, DeletedAt), not a pure join table.

1. Run this code on startup

    db.AutoMigrate(&entity.Item{}, &entity.ParentChildItem{})
    err := db.SetupJoinTable(&entity.Item{}, "ChildItems", &entity.ParentChildItem{})
    if err != nil {
        panic(fmt.Sprintf("Failed to setup join table: %v", err))
    }