Fix unexpected alter table in auto migration, close #5942, #5943

migrator/migrator.go

@@ -120,7 +120,10 @@ func (m Migrator) AutoMigrate(values ...interface{}) error {
 				if err != nil {
 					return err
 				}
-
+				var (
+					parseIndexes          = stmt.Schema.ParseIndexes()
+					parseCheckConstraints = stmt.Schema.ParseCheckConstraints()
+				)
 				for _, dbName := range stmt.Schema.DBNames {
 					field := stmt.Schema.FieldsByDBName[dbName]
 					var foundColumn gorm.ColumnType
@@ -157,15 +160,15 @@ func (m Migrator) AutoMigrate(values ...interface{}) error {
 					}
 				}
 
-				for _, chk := range stmt.Schema.ParseCheckConstraints() {
+				for _, chk := range parseCheckConstraints {
 					if !queryTx.Migrator().HasConstraint(value, chk.Name) {
 						if err := execTx.Migrator().CreateConstraint(value, chk.Name); err != nil {
 							return err
 						}
 					}
 				}
 
-				for _, idx := range stmt.Schema.ParseIndexes() {
+				for _, idx := range parseIndexes {
 					if !queryTx.Migrator().HasIndex(value, idx.Name) {
 						if err := execTx.Migrator().CreateIndex(value, idx.Name); err != nil {
 							return err
@@ -430,7 +433,8 @@ func (m Migrator) MigrateColumn(value interface{}, field *schema.Field, columnTy
 	realDataType := strings.ToLower(columnType.DatabaseTypeName())
 
 	var (
-		alterColumn, isSameType bool
+		alterColumn bool
+		isSameType  = fullDataType == realDataType
 	)
 
 	if !field.PrimaryKey {

schema/index.go

@@ -129,6 +129,7 @@ func parseFieldIndexes(field *Field) (indexes []Index, err error) {
 				}
 
 				if (k == "UNIQUEINDEX") || settings["UNIQUE"] != "" {
+					field.Unique = true
 					settings["CLASS"] = "UNIQUE"
 				}
 

tests/go.mod

@@ -13,7 +13,7 @@ require (
 	gorm.io/driver/postgres v1.4.6
 	gorm.io/driver/sqlite v1.4.4
 	gorm.io/driver/sqlserver v1.4.1
-	gorm.io/gorm v1.24.2
+	gorm.io/gorm v1.24.3
 )
 
 replace gorm.io/gorm => ../

tests/migrate_test.go

@@ -1270,6 +1270,38 @@ func TestMigrateDefaultNullString(t *testing.T) {
 	AssertEqual(t, ok, false)
 }
 
+func TestMigrateMySQLWithCustomizedTypes(t *testing.T) {
+	if DB.Dialector.Name() != "mysql" {
+		t.Skip()
+	}
+
+	type MyTable struct {
+		Def string `gorm:"size:512;index:idx_def,unique"`
+		Abc string `gorm:"size:65000000"`
+	}
+
+	DB.Migrator().DropTable("my_tables")
+
+	sql := "CREATE TABLE `my_tables` (`def` varchar(512),`abc` longtext,UNIQUE INDEX `idx_def` (`def`))"
+	if err := DB.Exec(sql).Error; err != nil {
+		t.Errorf("Failed, got error: %v", err)
+	}
+
+	session := DB.Session(&gorm.Session{Logger: Tracer{
+		Logger: DB.Config.Logger,
+		Test: func(ctx context.Context, begin time.Time, fc func() (sql string, rowsAffected int64), err error) {
+			sql, _ := fc()
+			if strings.HasPrefix(sql, "ALTER TABLE") {
+				t.Errorf("shouldn't execute: sql=%s", sql)
+			}
+		},
+	}})
+
+	if err := session.AutoMigrate(&MyTable{}); err != nil {
+		t.Errorf("Failed, got error: %v", err)
+	}
+}
+
 func TestMigrateIgnoreRelations(t *testing.T) {
 	type RelationModel1 struct {
 		ID uint