Edit DB.clone(), DB.Dialect(), and Scope.Dialect() preserve transactions (#1939)

* Edit DB.clone(), DB.Dialect(), and Scope.Dialect() preserve transactions.

* Adds a test case for tables creations and autoMigrate in the same transaction.

main.go

@@ -119,7 +119,7 @@ func (s *DB) CommonDB() SQLCommon {
 
 // Dialect get dialect
 func (s *DB) Dialect() Dialect {
-	return s.parent.dialect
+	return s.dialect
 }
 
 // Callback return `Callbacks` container, you could add/change/delete callbacks with it
@@ -484,6 +484,8 @@ func (s *DB) Begin() *DB {
 	if db, ok := c.db.(sqlDb); ok && db != nil {
 		tx, err := db.Begin()
 		c.db = interface{}(tx).(SQLCommon)
+
+		c.dialect.SetDB(c.db)
 		c.AddError(err)
 	} else {
 		c.AddError(ErrCantStartTransaction)
@@ -748,6 +750,7 @@ func (s *DB) clone() *DB {
 		Value:             s.Value,
 		Error:             s.Error,
 		blockGlobalUpdate: s.blockGlobalUpdate,
+		dialect:           newDialect(s.dialect.GetName(), s.db),
 	}
 
 	for key, value := range s.values {

migration_test.go

@@ -398,6 +398,53 @@ func TestAutoMigration(t *testing.T) {
 	}
 }
 
+func TestCreateAndAutomigrateTransaction(t *testing.T) {
+	tx := DB.Begin()
+
+	func() {
+		type Bar struct {
+			ID uint
+		}
+		DB.DropTableIfExists(&Bar{})
+
+		if ok := DB.HasTable("bars"); ok {
+			t.Errorf("Table should not exist, but does")
+		}
+
+		if ok := tx.HasTable("bars"); ok {
+			t.Errorf("Table should not exist, but does")
+		}
+	}()
+
+	func() {
+		type Bar struct {
+			Name string
+		}
+		err := tx.CreateTable(&Bar{}).Error
+
+		if err != nil {
+			t.Errorf("Should have been able to create the table, but couldn't: %s", err)
+		}
+
+		if ok := tx.HasTable(&Bar{}); !ok {
+			t.Errorf("The transaction should be able to see the table")
+		}
+	}()
+
+	func() {
+		type Bar struct {
+			Stuff string
+		}
+
+		err := tx.AutoMigrate(&Bar{}).Error
+		if err != nil {
+			t.Errorf("Should have been able to alter the table, but couldn't")
+		}
+	}()
+
+	tx.Rollback()
+}
+
 type MultipleIndexes struct {
 	ID     int64
 	UserID int64  `sql:"unique_index:uix_multipleindexes_user_name,uix_multipleindexes_user_email;index:idx_multipleindexes_user_other"`

scope.go

@@ -63,7 +63,7 @@ func (scope *Scope) SQLDB() SQLCommon {
 
 // Dialect get dialect
 func (scope *Scope) Dialect() Dialect {
-	return scope.db.parent.dialect
+	return scope.db.dialect
 }
 
 // Quote used to quote string to escape them for database