Add method HasTable, HasColumn to dialect

dialect.go

@@ -14,6 +14,8 @@ type Dialect interface {
 	PrimaryKeyTag(value reflect.Value, size int) string
 	ReturningStr(key string) string
 	Quote(key string) string
+	HasTable(scope *Scope, tableName string) bool
+	HasColumn(scope *Scope, tableName string, columnName string) bool
 }
 
 func NewDialect(driver string) Dialect {

mysql.go

@@ -68,10 +68,21 @@ func (s *mysql) Quote(key string) string {
 	return fmt.Sprintf("`%s`", key)
 }
 
-func (s *mysql) HasTable(tableName string) bool {
+func (s *mysql) HasTable(scope *Scope, tableName string) bool {
-	return true
+	var count int
+	newScope := scope.New(nil)
+	newScope.Raw(fmt.Sprintf("SELECT count(*) FROM INFORMATION_SCHEMA.tables where table_name = %v", newScope.AddToVars(tableName)))
+	newScope.DB().QueryRow(newScope.Sql, newScope.SqlVars...).Scan(&count)
+	return count > 0
 }
 
-func (s *mysql) HasColumn(tableName string, columnName string) bool {
+func (s *mysql) HasColumn(scope *Scope, tableName string, columnName string) bool {
-	return true
+	var count int
+	newScope := scope.New(nil)
+	newScope.Raw(fmt.Sprintf("SELECT count(*) FROM information_schema.columns WHERE table_name = %v AND column_name = %v",
+		newScope.AddToVars(tableName),
+		newScope.AddToVars(columnName),
+	))
+	newScope.DB().QueryRow(newScope.Sql, newScope.SqlVars...).Scan(&count)
+	return count > 0
 }

postgres.go

@@ -61,3 +61,22 @@ func (s *postgres) ReturningStr(key string) string {
 func (s *postgres) Quote(key string) string {
 	return fmt.Sprintf("\"%s\"", key)
 }
+
+func (s *postgres) HasTable(scope *Scope, tableName string) bool {
+	var count int
+	newScope := scope.New(nil)
+	newScope.Raw(fmt.Sprintf("SELECT count(*) FROM INFORMATION_SCHEMA.tables where table_name = %v", newScope.AddToVars(tableName)))
+	newScope.DB().QueryRow(newScope.Sql, newScope.SqlVars...).Scan(&count)
+	return count > 0
+}
+
+func (s *postgres) HasColumn(scope *Scope, tableName string, columnName string) bool {
+	var count int
+	newScope := scope.New(nil)
+	newScope.Raw(fmt.Sprintf("SELECT count(*) FROM information_schema.columns WHERE table_name = %v AND column_name = %v",
+		newScope.AddToVars(tableName),
+		newScope.AddToVars(columnName),
+	))
+	newScope.DB().QueryRow(newScope.Sql, newScope.SqlVars...).Scan(&count)
+	return count > 0
+}

scope_private.go

@@ -447,31 +447,17 @@ func (scope *Scope) removeIndex(indexName string) {
 }
 
 func (scope *Scope) autoMigrate() *Scope {
-	var tableName string
+	if !scope.Dialect().HasTable(scope, scope.TableName()) {
-	scope.Raw(fmt.Sprintf("SELECT table_name FROM INFORMATION_SCHEMA.tables where table_name = %v",
-		scope.AddToVars(scope.TableName())))
-	scope.DB().QueryRow(scope.Sql, scope.SqlVars...).Scan(&tableName)
-	scope.SqlVars = []interface{}{}
-
-	// If table doesn't exist
-	if len(tableName) == 0 {
 		scope.createTable()
 	} else {
 		for _, field := range scope.Fields() {
-			var column, data string
+			if !scope.Dialect().HasColumn(scope, scope.TableName(), field.DBName) {
-			scope.Raw(fmt.Sprintf("SELECT column_name, data_type FROM information_schema.columns WHERE table_name = %v AND column_name = %v",
+				if len(field.SqlTag) > 0 && !field.IsIgnored {
-				scope.AddToVars(scope.TableName()),
-				scope.AddToVars(field.DBName),
-			))
-			scope.DB().QueryRow(scope.Sql, scope.SqlVars...).Scan(&column, &data)
-			scope.SqlVars = []interface{}{}
-
-			// If column doesn't exist
-			if len(column) == 0 && len(field.SqlTag) > 0 && !field.IsIgnored {
 					scope.Raw(fmt.Sprintf("ALTER TABLE %v ADD %v %v;", scope.TableName(), field.DBName, field.SqlTag)).Exec()
 				}
 			}
 		}
+	}
 	return scope
 }
 

sqlite3.go

@@ -52,10 +52,29 @@ func (s *sqlite3) PrimaryKeyTag(value reflect.Value, size int) string {
 	}
 }
 
-func (s *sqlite3) ReturningStr(key string) (str string) {
+func (s *sqlite3) ReturningStr(key string) string {
-	return
+	return ""
 }
 
-func (s *sqlite3) Quote(key string) (str string) {
+func (s *sqlite3) Quote(key string) string {
 	return fmt.Sprintf("\"%s\"", key)
 }
+
+func (s *sqlite3) HasTable(scope *Scope, tableName string) bool {
+	var count int
+	newScope := scope.New(nil)
+	newScope.Raw(fmt.Sprintf("SELECT count(*) FROM INFORMATION_SCHEMA.tables where table_name = %v", newScope.AddToVars(tableName)))
+	newScope.DB().QueryRow(newScope.Sql, newScope.SqlVars...).Scan(&count)
+	return count > 0
+}
+
+func (s *sqlite3) HasColumn(scope *Scope, tableName string, columnName string) bool {
+	var count int
+	newScope := scope.New(nil)
+	newScope.Raw(fmt.Sprintf("SELECT count(*) FROM information_schema.columns WHERE table_name = %v AND column_name = %v",
+		newScope.AddToVars(tableName),
+		newScope.AddToVars(columnName),
+	))
+	newScope.DB().QueryRow(newScope.Sql, newScope.SqlVars...).Scan(&count)
+	return count > 0
+}