Bug when changing an existing column property from a state with a default value to a state without a default value

[wookie0]

GORM Playground Link

Sorry, It's such an obvious bug that I don't think there's any need for example code.

Description

The code below does not take some cases into account. I think this is a bug. There is a default value in the existing column property, but if the column property to be changed does not have a default value, no processing is performed. I think if field.HasDefaultValue is false, you need to perform a DROP DEFAULT query.

postgres/migrator.go

Lines 383 to 401 in 0d37bf2

	if v, ok := fieldColumnType.DefaultValue(); (field.DefaultValueInterface == nil && ok) || v != field.DefaultValue {
	if field.HasDefaultValue && (field.DefaultValueInterface != nil || field.DefaultValue != "") {
	if field.DefaultValueInterface != nil {
	defaultStmt := &gorm.Statement{Vars: []interface{}{field.DefaultValueInterface}}
	m.Dialector.BindVarTo(defaultStmt, defaultStmt, field.DefaultValueInterface)
	if err := m.DB.Exec("ALTER TABLE ? ALTER COLUMN ? SET DEFAULT ?", m.CurrentTable(stmt), clause.Column{Name: field.DBName}, clause.Expr{SQL: m.Dialector.Explain(defaultStmt.SQL.String(), field.DefaultValueInterface)}).Error; err != nil {
	return err
	}
	} else if field.DefaultValue != "(-)" {
	if err := m.DB.Exec("ALTER TABLE ? ALTER COLUMN ? SET DEFAULT ?", m.CurrentTable(stmt), clause.Column{Name: field.DBName}, clause.Expr{SQL: field.DefaultValue}).Error; err != nil {
	return err
	}
	} else {
	if err := m.DB.Exec("ALTER TABLE ? ALTER COLUMN ? DROP DEFAULT", m.CurrentTable(stmt), clause.Column{Name: field.DBName}, clause.Expr{SQL: field.DefaultValue}).Error; err != nil {
	return err
	}
	}
	}
	}