return assocDB.Updates(fkNil).Error
		case clause.OpDelete:
			return assocDB.Delete(assocModel).Error
		case clause.OpUpdate:
			return assocDB.Updates(setMap).Error
		}
	case schema.BelongsTo:
		switch op.Type {
		case clause.OpDelete:
			return base.Transaction(func(tx *DB) error {
				assocDB.Statement.ConnPool = tx.Statement.ConnPool
				base.Statement.ConnPool = tx.Statement.ConnPool