feat: add support for setting nullable

dialect.go

@@ -37,6 +37,8 @@ type Dialect interface {
 	HasColumn(tableName string, columnName string) bool
 	// ModifyColumn modify column's type
 	ModifyColumn(tableName string, columnName string, typ string) error
+	// Nullable sets column's null constraint
+ 	Nullable(tableName string, columnName string, colType string, isNull bool) error
 
 	// LimitAndOffsetSQL return generated SQL with Limit and Offset, as mssql has special case
 	LimitAndOffsetSQL(limit, offset interface{}) string

dialect_common.go

@@ -139,6 +139,16 @@ func (s commonDialect) ModifyColumn(tableName string, columnName string, typ str
 	return err
 }
 
+func (s commonDialect) Nullable(tableName string, columnName string, colType string, isNull bool) error {
+	var err error
+	if isNull {
+		_, err = s.db.Exec(fmt.Sprintf("ALTER TABLE %v MODIFY %v %v NULL", tableName, columnName, colType))
+	} else {
+		_, err = s.db.Exec(fmt.Sprintf("ALTER TABLE %v MODIFY %v %v NOT NULL", tableName, columnName, colType))
+	}
+	return err
+}
+
 func (s commonDialect) CurrentDatabase() (name string) {
 	s.db.QueryRow("SELECT DATABASE()").Scan(&name)
 	return

dialect_oci8.go

@@ -129,6 +129,16 @@ func (o *oci8) HasColumn(tableName string, columnName string) bool {
 	return count > 0
 }
 
+func (s *oci8) Nullable(tableName string, columnName string, colType string, isNull bool) error {
+	var err error
+	if isNull {
+		_, err = s.db.Exec(fmt.Sprintf("ALTER TABLE %v MODIFY %v NULL", tableName, columnName))
+	} else {
+		_, err = s.db.Exec(fmt.Sprintf("ALTER TABLE %v MODIFY %v NOT NULL", tableName, columnName))
+	}
+	return err
+}
+
 
 func (*oci8) buildSha(str string) string {
 	if utf8.RuneCountInString(str) <= 30 {

dialect_postgres.go

@@ -115,6 +115,16 @@ func (s postgres) HasColumn(tableName string, columnName string) bool {
 	return count > 0
 }
 
+func (s postgres) Nullable(tableName string, columnName string, colType string, isNull bool) error {
+	var err error
+	if isNull {
+		_, err = s.db.Exec(fmt.Sprintf("ALTER TABLE %v ALTER COLUMN %v DROP NOT NULL", tableName, columnName))
+	} else {
+		_, err = s.db.Exec(fmt.Sprintf("ALTER TABLE %v ALTER COLUMN %v SET NOT NULL", tableName, columnName))
+	}
+	return err
+}
+
 func (s postgres) CurrentDatabase() (name string) {
 	s.db.QueryRow("SELECT CURRENT_DATABASE()").Scan(&name)
 	return

main.go

@@ -666,6 +666,13 @@ func (s *DB) ModifyColumn(column string, typ string) *DB {
 	return scope.db
 }
 
+// Nullable sets column's null constraint
+func (s *DB) Nullable(column string, isNull bool) *DB {
+	scope := s.NewScope(s.Value)
+	scope.nullable(column, isNull)
+	return scope.db
+}
+
 // DropColumn drop a column
 func (s *DB) DropColumn(column string) *DB {
 	scope := s.NewScope(s.Value)

scope.go

@@ -1223,6 +1223,15 @@ func (scope *Scope) modifyColumn(column string, typ string) {
 	scope.db.AddError(scope.Dialect().ModifyColumn(scope.QuotedTableName(), scope.Quote(column), typ))
 }
 
+func (scope *Scope) nullable(column string, isNull bool) {
+	colField, ok := scope.FieldByName(column)
+	if !ok {
+		scope.db.AddError(errors.New("No such column found"))
+	}
+	colType := scope.Dialect().DataTypeOf(colField.StructField)
+	scope.db.AddError(scope.Dialect().Nullable(scope.QuotedTableName(), scope.Quote(column), colType, isNull))
+}
+
 func (scope *Scope) dropColumn(column string) {
 	scope.Raw(fmt.Sprintf("ALTER TABLE %v DROP COLUMN %v", scope.QuotedTableName(), scope.Quote(column))).Exec()
 }