Migrate nullable fix

oracle/migrator.go

@@ -308,15 +308,47 @@ func (m Migrator) DropColumn(value interface{}, name string) error {
 func (m Migrator) AlterColumn(value interface{}, field string) error {
 	return m.RunWithValue(value, func(stmt *gorm.Statement) error {
 		if stmt.Schema != nil {
-			if field := stmt.Schema.LookUpField(field); field != nil {
-				fileType := m.FullDataTypeOf(field)
+			if f := stmt.Schema.LookUpField(field); f != nil {
+				columnTypes, err := m.ColumnTypes(value)
+				if err != nil {
+					return err
+				}
+
+				var currentNullable bool
+				var currentType string
+				for _, col := range columnTypes {
+					if strings.EqualFold(col.Name(), f.DBName) {
+						currentNullable, _ = col.Nullable()
+						currentType = strings.ToUpper(col.DatabaseTypeName())
+						break
+					}
+				}
+
+				desiredNullable := !f.NotNull
+				desiredType := strings.ToUpper(m.DataTypeOf(f))
+
+				// nullable → non-nullable → skip
+				if currentNullable && !desiredNullable {
+					return nil
+				}
+
+				// same type + same nullability → skip
+				if currentNullable == desiredNullable && strings.Contains(currentType, desiredType) {
+					return nil
+				}
+
+				sql := "ALTER TABLE ? MODIFY ? " + m.DataTypeOf(f)
+				if f.NotNull {
+					sql += " NOT NULL"
+				} else if !currentNullable && desiredNullable {
+					sql += " NULL"
+				}
+
 				return m.DB.Exec(
-					"ALTER TABLE ? MODIFY ? ?",
+					sql,
 					clause.Table{Name: stmt.Schema.Table},
-					clause.Column{Name: field.DBName},
-					fileType,
+					clause.Column{Name: f.DBName},
 				).Error
-
 			}
 		}
 		return fmt.Errorf("failed to look up field with name: %s", field)

tests/migrate_test.go

@@ -186,7 +186,6 @@ func TestAutoMigrateSelfReferential(t *testing.T) {
 }
 
 func TestAutoMigrateNullable(t *testing.T) {
-	t.Skip()
 	type MigrateNullableColumn struct {
 		ID    uint
 		Bonus float64 `gorm:"not null"`
@@ -1397,7 +1396,7 @@ func TestMigrateExistingBoolColumnPG(t *testing.T) {
 
 func TestMigrateWithUniqueIndexAndUnique(t *testing.T) {
 	t.Skip()
-	
+
 	const table = "unique_struct"
 
 	checkField := func(model interface{}, fieldName string, unique bool, uniqueIndex string) {

tests/passed-tests.txt

@@ -163,7 +163,7 @@ TestSetAndGet
 TestMigrate
 TestAutoMigrateInt8PG
 TestAutoMigrateSelfReferential
-#TestAutoMigrateNullable
+TestAutoMigrateNullable
 TestSmartMigrateColumn
 TestMigrateWithColumnComment
 TestMigrateWithUniqueIndex