Added nested transaction support.

Added test cases showing transaction support scenarios.

persistence/implementation/common/database/database_connection.e

@@ -131,6 +131,142 @@ feature -- Transactions
 			retry
 		end
 
+
+feature --
+
+	is_connected_to_storage: BOOLEAN
+			-- Is connected to the database
+		do
+			Result := db_control.is_connected
+		end
+
+feature -- Transaction Status
+
+	in_transaction_session: BOOLEAN
+			-- Is session started?
+
+	transaction_session_depth: INTEGER
+			-- Depth in the transaction session
+
+feature -- Transaction Operation
+
+	begin_transaction2
+			-- Start session
+			-- if already started, increase the `transaction_session_depth'
+		require
+			in_transaction_session implies transaction_session_depth > 0
+			not in_transaction_session implies transaction_session_depth = 0
+		local
+			l_session_control: like db_control
+			l_retried: INTEGER
+		do
+			if l_retried = 0 then
+				if not in_transaction_session then
+					database_error_handler.reset
+
+					check transaction_session_depth = 0 end
+
+					debug ("database_session")
+						print ("..Start session%N")
+					end
+					connect -- connect the DB
+					if is_connected_to_storage then
+						in_transaction_session := True
+						db_control.begin -- start transaction
+					else
+						l_session_control := db_control
+						if not l_session_control.is_ok then
+							database_error_handler.add_database_error (l_session_control.error_message_32, l_session_control.error_code)
+						else
+							database_error_handler.add_database_error ("Session_not_started_error_message", 0)
+						end
+						l_session_control.reset
+					end
+				end
+				transaction_session_depth := transaction_session_depth + 1
+			else
+				if l_retried = 1 then
+					transaction_session_depth := transaction_session_depth + 1
+					if attached (create {EXCEPTION_MANAGER}).last_exception as e then
+						if attached {ASSERTION_VIOLATION} e then
+							--| Ignore for now with MYSQL ...
+						else
+							exception_as_error (e)
+						end
+					end
+
+					in_transaction_session := False
+					db_control.reset
+				else
+					in_transaction_session := False
+				end
+			end
+		ensure
+			transaction_session_depth = (old transaction_session_depth) + 1
+		rescue
+			l_retried := l_retried + 1
+			retry
+		end
+
+	commit2
+			-- End session
+		local
+			l_retried: BOOLEAN
+		do
+			if not l_retried then
+				transaction_session_depth := transaction_session_depth - 1
+				if transaction_session_depth = 0 then
+					debug ("database_session")
+						print ("..End session%N")
+					end
+					if is_connected_to_storage then
+						if not database_error_handler.has_error then
+							db_control.commit -- Commit transaction
+						else
+							db_control.rollback  -- Rollback transaction
+						end
+					end
+					in_transaction_session := False
+				end
+			else
+				exception_as_error ((create {EXCEPTION_MANAGER}).last_exception)
+				in_transaction_session := False
+				transaction_session_depth := transaction_session_depth - 1
+				db_control.reset
+			end
+		rescue
+			l_retried := True
+			retry
+		end
+
+
+
+	rollback2
+			-- End session
+		local
+			l_retried: BOOLEAN
+		do
+			if not l_retried then
+				transaction_session_depth := transaction_session_depth - 1
+				if transaction_session_depth = 0 then
+					debug ("database_session")
+						print ("..End session%N")
+					end
+					if is_connected_to_storage then
+						db_control.rollback  -- Rollback transaction
+					end
+					in_transaction_session := False
+				end
+			else
+				exception_as_error ((create {EXCEPTION_MANAGER}).last_exception)
+				in_transaction_session := False
+				transaction_session_depth := transaction_session_depth - 1
+				db_control.reset
+			end
+		rescue
+			l_retried := True
+			retry
+		end
 feature -- Change Element
 
 	not_keep_connection