// Views
	CreateView(name string, option ViewOption) error
	DropView(name string) error

	// Constraints
	CreateConstraint(dst interface{}, name string) error
	DropConstraint(dst interface{}, name string) error
	HasConstraint(dst interface{}, name string) bool

	// Indexes
	CreateIndex(dst interface{}, name string) error
	DropIndex(dst interface{}, name string) error

			}
			sql, values := constraint.Build()
			return m.DB.Exec("ALTER TABLE ? ADD "+sql, append(vars, values...)...).Error
		}
		return nil
	})
}

// DropConstraint drop constraint
func (m Migrator) DropConstraint(value interface{}, name string) error {
	return m.RunWithValue(value, func(stmt *gorm.Statement) error {
		constraint, table := m.GuessConstraintInterfaceAndTable(stmt, name)
		if constraint != nil {

	for _, name := range names {
		if !DB.Migrator().HasConstraint(&User{}, name) {
			DB.Migrator().CreateConstraint(&User{}, name)
		}

		if err := DB.Migrator().DropConstraint(&User{}, name); err != nil {
			t.Fatalf("failed to drop constraint %v, got error %v", name, err)
		}

		if DB.Migrator().HasConstraint(&User{}, name) {
			t.Fatalf("constraint %v should been deleted", name)
		}