maintenance

The Maintenance plugin can be used in combination with the solution import hooks to execute business logic when importing solutions into the Servoy Application Server. The Maintenance plugin allows to programatically perform administrative tasks that can otherwise only be performed manually on the Servoy Admin page.

Next to that, the Maintenance plugin also allows the developer to take control over the data model modifications.

Solution Import Hooks
During solution import from the Servoy Admin Page, modules with certain name patterns are handled in a special way. Modules whose names start with "before_import" are handled as pre-import hooks. Their onOpen event handlers are executed before the solution is actually imported. Similarly, modules whose names start with "after_import" are handled as post-import hooks. Their onOpen event handlers are executed after the solution is actually imported.

If you have several modules that start with "before_import" or "after_import", they will be all handled in this way, but no handling order is guaranteed. It is recommended that you have at most one pre-import and at most one post-import hook in your exported solutions.

During the execution of the onOpen event handlers from the pre-import and post-import hooks, any output printed with application.output(...) will be redirected to the import log, which you can see in the Servoy Admin page.

The pre-import and post-import hooks were introduced for allowing you to automatically perform administrative tasks on the server while importing solutions:

• Send messages to connected clients, or even kill connected clients.
• Put the server into maintenance mode for the duration of the solution import.
• Perform operations on databases.
  
  These operations can be performed through the maintenance plugin, which is available since version 4.2 of Servoy. The maintenance plugin was designed specifically for being used with solution import hooks. Please consult its API documentation for specific details about available functions.
  
  A typical scenario of using the solution import hooks is the following:
• Before importing the solution, connected clients are notified that an import will take place, then they are disconnected and then the server is put into maintenance mode, so that no new clients can connect during the import.
• The import is performed as usual.
• After the import is over, the server is taken out of maintenance mode, so that clients can connect again.
  
  All these steps can be automated if you create a pre-import and a post-import hook module. The pre-import hook module can have the following function set as its onOpen event handler:

  
  function onBeforeImportSolutionOpen()
  {
  	application.output("Notifying and disconnecting connected clients...");
  	plugins.maintenance.sendMessageToAllClients("A solution upgrade will take place on the server. You will be disconnected in 2 minutes.");
  	application.sleep(2 * 60 * 1000);
  	plugins.maintenance.sendMessageToAllClients("A solution upgrade will take place on the server. You will be disconnected NOW.");
  	plugins.maintenance.shutDownAllClients();
  	application.output("Putting server into maintenance mode...");
  	plugins.maintenance.setMaintenanceMode(true);
  	application.output("Proceeding to import...");
  }
  

  
  The function sends a notification to all connected clients, telling them that in two minutes (or any other amount of time that should be enough for clients to save any important data) they will be disconnected. The function waits for two minutes, then it sends another message to the clients, telling them that they will be immediately disconnected. Then all connected clients are killed and then the Server is put into maintenance mode. From this moment on, no new client will be able to connect to the Server.
  
  The post-import hook module can have the following function as its onOpen event handler:

  
  function onAfterImportSolutionOpen()
  {
  	application.output("Taking server out of maintenance mode.");
  	plugins.maintenance.setMaintenanceMode(false);
  	application.output("Clients can now connect to the server.");
  }
  

  
  This function takes the Server out of maintenance mode, so that clients can again connect to it.
  
  Modifying Database Structure and Content
  Using the Maintenance plugin, it is possible to programmatically modify the database structure. You can create and drop tables, and you can create and delete columns.
  
  It can happen that when you upgrade your Servoy solution, you need to change the structure of the underlying database. Some columns may become obsolete, new columns may be needed, data may need to be reorganized, etc. You can automate all these tasks by using the Maintenance plugin in a pre-import hook.
  
  For example the following function, set as handler for the onOpen even of a pre-import hook, will delete a no longer needed column from a table.
  

  
  function onSolutionOpenBeforeImport()
  {
  	var server = plugins.maintenance.getServer("example_data")
  	if (server) {
  		var table = server.getTable("todo_list")
  		if (table) {
  			table.deleteColumn("todo_list_suggested_by")
  			var result = server.synchronizeWithDB(table)
  			if (result)
  				application.output("'Suggested By' column removed.")
  			else
  				application.output("Something went wrong while deleting column.")
  		}
  		else {
  			application.output("Table 'todo_list' cannot be found.")
  		}
  	}
  	else {
  		application.output("Server 'example_data' cannot be found.")
  	}
  }
  

  
  
  The function tries to obtain a reference to the server where the table is stored. If successful, then it tries to obtain a reference to the table which holds the obsolete column. If this step is also successful, then it deletes the column. In order to make the change permanent, the table must be synchronized with the underlying database.
  
  In pre-import and post-import hooks, besides changing the database structure, you can also change the database content. This is done in the classical way, by using the foundset API.

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var clients = plugins.maintenance.getConnectedClients();
application.output("There are " + clients.length + " connected clients.");
for (var i = 0; i < clients.length; i++)
	application.output("Client has clientId '" + clients[i].getClientId() + "' and has connected from host '" + clients[i].getHostAddress() + "'.");

var serverNames = plugins.maintenance.getDataModelClonesFrom('my_server');
for (var i=0; i<serverNames.length; i++)
	application.output("Process server " + i + ": " + serverNames[i]);

var server = plugins.maintenance.getServer("example_data");
if (server) {
	var tableNames = server.getTableNames();
	application.output("There are " + tableNames.length + " tables.");
	for (var i=0; i<tableNames.length; i++)
		application.output("Table " + i + ": " + tableNames[i]);
	}
else {
	plugins.dialogs.showInfoDialog("Attention","Server 'example_data' cannot be found.","OK");
}

var serverNames = plugins.maintenance.getServerNames();
application.output("There are " + serverNames.length + " servers.");
for (var i=0; i<serverNames.length; i++)
	application.output("Server " + i + ": " + serverNames[i]);

if (plugins.maintenance.isInMaintenanceMode())
	application.output("Server is in maintenance mode.");
else
	application.output("Server is not in maintenance mode.");

plugins.maintenance.sendMessageToAllClients("Hello, all clients!");

var clients = plugins.maintenance.getConnectedClients();
for (var i=0; i<clients.length; i++)
	plugins.maintenance.sendMessageToClient(clients[i].getClientId(), "Hello, client " + clients[i].getClientId() + "!");

plugins.maintenance.setMaintenanceMode(!plugins.maintenance.isInMaintenanceMode());

plugins.maintenance.shutDownAllClients();

var clients = plugins.maintenance.getConnectedClients();
for (var i=0; i<clients.length; i++)
	plugins.maintenance.shutDownClient(clients[i].getClientId());