gorm/dialects/mysql/migrator.go

package mysql

import (
	"fmt"

	"github.com/jinzhu/gorm"
	"github.com/jinzhu/gorm/clause"
	"github.com/jinzhu/gorm/migrator"
)

type Migrator struct {
	migrator.Migrator
}

func (m Migrator) AlterColumn(value interface{}, field string) error {
	return m.RunWithValue(value, func(stmt *gorm.Statement) error {
		if field := stmt.Schema.LookUpField(field); field != nil {
			return m.DB.Exec(
				"ALTER TABLE ? MODIFY COLUMN ? TYPE ?",
				clause.Table{Name: stmt.Table}, clause.Column{Name: field.DBName}, clause.Expr{SQL: field.DBDataType},
			).Error
		}
		return fmt.Errorf("failed to look up field with name: %s", field)
	})
}

func (m Migrator) DropConstraint(value interface{}, name string) error {
	return m.RunWithValue(value, func(stmt *gorm.Statement) error {
		for _, chk := range stmt.Schema.ParseCheckConstraints() {
			if chk.Name == name {
				return m.DB.Exec(
					"ALTER TABLE ? DROP CHECK ?",
					clause.Table{Name: stmt.Table}, clause.Column{Name: name},
				).Error
			}
		}

		return m.DB.Exec(
			"ALTER TABLE ? DROP FOREIGN KEY ?",
			clause.Table{Name: stmt.Table}, clause.Column{Name: name},
		).Error
	})
}