add support for nested transactions

while here:
- don't allow to copy/move DbConnector

src/dbconnector.cpp

@@ -51,16 +51,9 @@ DbConnector::DbConnector()
 	expression_allocated = false;
 	log = nullptr;
 	log_queries = false;
+	transaction_index = 0;
 }
 
-DbConnector::DbConnector(const DbConnector &)
-{
-	db_expression = nullptr;
-	expression_allocated = false;
-	log = nullptr;
-}
-
-
 DbConnector::~DbConnector()
 {
 	deallocate_expression();
@@ -173,6 +166,206 @@ bool DbConnector::query_remove(const pt::TextStream & stream, QueryResult & quer
 }
 
 
+bool DbConnector::begin()
+{
+	bool status = false;
+
+	if( transaction_index > 0 )
+	{
+		pt::TextStream str;
+		str << "SAVEPOINT savepoint_" << transaction_index;
+		status = DbConnector::query(str);
+	}
+	else
+	{
+		status = DbConnector::query("BEGIN");
+	}
+
+	if( status )
+	{
+		transaction_index += 1;
+	}
+	else
+	{
+		if( log )
+		{
+			(*log) << pt::Log::log1 << "Morm: I cannot start a transaction" << pt::Log::logend;
+		}
+	}
+
+	return status;
+}
+
+
+bool DbConnector::begin_if_needed()
+{
+	bool status = true;
+
+	if( transaction_index == 0 )
+	{
+		status = begin();
+	}
+
+	return status;
+}
+
+
+bool DbConnector::rollback()
+{
+	return rollback(transaction_index);
+}
+
+
+bool DbConnector::commit()
+{
+	return commit(transaction_index);
+}
+
+
+
+bool DbConnector::rollback_one_transaction(size_t index)
+{
+	bool status = false;
+
+	if( index > 1 )
+	{
+		pt::TextStream str;
+		str << "ROLLBACK TO SAVEPOINT savepoint_" << (index - 1);
+		status = DbConnector::query(str);
+		transaction_index = index - 1; // decrement it even if rollback failed
+	}
+	else
+	if( index == 1 )
+	{
+		status = DbConnector::query("ROLLBACK");
+		transaction_index = 0;
+	}
+
+	return status;
+}
+
+
+
+
+bool DbConnector::rollback(size_t index)
+{
+	bool status = false;
+
+	if( index == 0 )
+	{
+		if( log )
+		{
+			(*log) << pt::Log::log1 << "Morm: there is no a transaction with zero index - skipping rollback";
+		}
+	}
+	else
+	if( index > transaction_index )
+	{
+		if( log )
+		{
+			(*log) << pt::Log::log1 << "Morm: transaction";
+
+			if( index > 1 )
+				(*log) << " for savepoint_" << (index-1);
+
+			(*log) << " does not exist - skipping rollback" << pt::Log::logend;
+		}
+	}
+	else
+	{
+		status = true;
+
+		for(size_t i = transaction_index ; i >= index ; --i)
+		{
+			if( !rollback_one_transaction(i) )
+			{
+				/*
+				 * return false if at least one rollback failed
+				 */
+				status = false;
+			}
+		}
+	}
+
+	return status;
+}
+
+
+bool DbConnector::commit_one_transaction(size_t index)
+{
+	bool status = false;
+
+	if( index > 1 )
+	{
+		pt::TextStream str;
+		str << "RELEASE SAVEPOINT savepoint_" << (index - 1);
+		status = DbConnector::query(str);
+		transaction_index = index - 1;
+	}
+	else
+	if( index == 1 )
+	{
+		status = DbConnector::query("COMMIT");
+		transaction_index = 0;
+	}
+
+	return status;
+}
+
+
+bool DbConnector::commit(size_t index)
+{
+	bool status = false;
+
+	if( index == 0 )
+	{
+		if( log )
+		{
+			(*log) << pt::Log::log1 << "Morm: there is no a transaction with zero index - skipping commit";
+		}
+	}
+	else
+	if( index > transaction_index )
+	{
+		if( log )
+		{
+			(*log) << pt::Log::log1 << "Morm: transaction";
+
+			if( index > 1 )
+				(*log) << " for savepoint_" << (index-1);
+
+			(*log) << " does not exist - skipping commit" << pt::Log::logend;
+		}
+	}
+	else
+	{
+		status = true;
+
+		for(size_t i = transaction_index ; i >= index ; --i)
+		{
+			if( !commit_one_transaction(i) )
+			{
+				/*
+				 * return false if at least one commit failed
+				 */
+				status = false;
+			}
+		}
+	}
+
+	return status;
+}
+
+
+
+
+
+size_t DbConnector::get_transaction_index()
+{
+	return transaction_index;
+}
+
+
 
 DbExpression * DbConnector::get_expression()
 {