In many applications, you need to filter data that is only relevant to the particular user that is logged in. For example, a personal information manager application may only want users to view their own tasks and not the tasks of other users. Here’s a walkthrough of how you can setup this kind of data filtering in Visual Studio LightSwitch.
I’ll first create a Task table which has two fields: one for the task description and another to store the user name of the user who created the task.
Next, I’ll need to write some code so that whenever a Task is created, it will automatically have it’s CreatedBy field set to the current user. To do this, I can use Write Code drop-down on the table designer to select the Created method.
Here’s the code:
partial void Task_Created()
this.CreatedBy = this.Application.User.Name;
Now we’re at the data filtering step. What I’d really like to do is have all queries for Tasks be filtered according to the current user. So even if I model a new query for Tasks then it will automatically get this filtering behavior. That way I only have to write this code once and it will be applied whenever tasks are queried. LightSwitch provides a built-in query for each table that returns all instances within that table. The name of this query is TableName_All. All other queries for that table are based on that All query. So if I can modify the behavior of that All query, then every other query that queries the same table will also get that behavior. LightSwitch just so happens to provide a way to modify the default behavior of the All query. This can be done through the PreprocessQuery method. This method is also available through the Write Code drop-down.
The PreprocessQuery method allows developers to modify the query before it is executed. In my case, I want to add a restriction to it so that only tasks created by the current user are returned.
partial void Tasks_All_PreprocessQuery(ref IQueryable<LightSwitchApplication.Task> query)
query = query.Where(t => t.CreatedBy == this.Application.User.Name);
And that’s all I need to do. Now, whenever any query is made for tasks it will add this restriction.