Thank you for joining me for this video. Maintenance plugin. For Servoy University, I'm Bob Cusick. The maintenance plugin was designed to allow you to change the schema or data before you do a solution import using either a before import or after import hook. It was not designed to be used inside of the web client or the smart client or even the headless client. So as long as we know that going in, let's talk about some of the functions and features that you can use in the maintenance plugin. We'll start out talking about some of the functions that you can do using the plugin to modify your schema or data before your solution import. So here we have get connected clients. You can get an array of all of the information about all of the clients that are currently connected. And when you do that, you get back a client information object for each of the connected clients. For each of the clients, you can determine how they're connected using the get application type. You can also get their ID, the host address, the host identifier, the host name, the user name that they're logged in under, and the user UUID. Coming back to the maintenance plugin functions, you can also use get data model clones from. So the idea here is that as you create database connections, you can mark them as being clones of another database connection. So you can tell how many servers you have to make the same changes to. You can also get all of the server names and you can filter that by valid enabled. You can sort them and you can choose whether or not you want to include duplicate names. So for example, in your pre import hook, you can verify to make sure that there is a valid and enabled server name before you do the import. You can also then go ahead and get an individual server and that returns a JS server object. So in the JS server object, you can do things like create a table, drop a table, you can get all the information about a table, and that will actually return a JS table object, which we'll get to in just a minute. You can get all of the table names, you can tell whether a table is valid or not. If you make any changes to your schema or your data, be the raw SQL plugin, you can go ahead and say reload data model and this will cause the server to refresh all of the information. You only need to use it if you're using the raw SQL plugin to modify your schema or data. If you're using the maintenance functions like create new table, drop table, then you can go ahead and say synchronize with DB. And so all of those changes that you make during your method will then be written and persisted to the backend database. Now I mentioned you can use this get table and that will return a JS table object. When you have a JS table object, you can do things like creating a new column, delete a column, get a column, get all the column names, get the quoted SQL name, get the raw identifier column names, and get the name of the SQL database, and also get the server name. So again, if you create columns, delete columns, then you would come back here to the JS server and you would use synchronize with DB and that would go ahead and persist all the changes that you made in your method. Coming back up to the main maintenance plugin again, you can tell if it's in maintenance mode, you can send a message to all of the clients to an individual client, you can set the maintenance mode and this is a Boolean that sets it to true or false. When you're in maintenance mode, that means that no other clients can actually connect to the server while it's in maintenance mode and you can choose to shut down all clients or choose to shut down a single client. Now again, remember this is really meant for pre import and post import of solutions only. It's not really meant to function inside of the smart client or the web client. To make this code actually run, you need to have a solution that starts with before import and if you want to execute things in a post import, then you have to have a solution named after import and it demonstrates how that would work. I've created a solution called before import and then you can put whatever else you want after the name, but it must start with before import for a pre import hook and it must start with after import for a post import hook. Once you've created your solution, then there's two things that you need to set. The first thing is it should be of type module and then you need to set the on open method. This is what's going to fire in your pre import hook. So I've created a global method. Let's see what that looks like here. So in this simple example, we're writing out application output, putting server in the maintenance mode. Now anything that you use for the application output during a pre import hook or a post import hook will actually be written to the server log so you can actually see those messages as they come through. Then we use the plug and put it into maintenance mode and then we actually go ahead and notify all clients that says a solution upgrade will take place on the server. You'll be disconnected in two minutes. And then we actually have a sleep command in here that will pause this method for two minutes that we sent another message that says, hey, you're going to go ahead and be disconnected now and it shuts down all of the connected clients regardless of how they're connected. And then the normal solution import will run. So what you need to do to make this a pre import hook is you need to include as a module into your solution this before import and if you want a post import hook, then you also need to include the module after import xxx or whatever you want it to be. In this example, we have a before solution import that put the server in the maintenance mode. Therefore we need to make sure that we have an after import module as well that will take this server out of maintenance mode or use the command plugins maintenance set maintenance mode to false. Otherwise no other clients will be able to connect. The maintenance plugin is a very powerful way for you to automatically alter the schema or data before you do your solution import. It also allows you to apply these same changes across multiple database servers in a SaaS setting. Thank you for watching.