Filtering data based on current user in LightSwitch apps

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.

Comments (6)
  1. jeremy says:

    Hi Matt great post, however, is there some additional post i'm missing?, i am not seeing wher you created the code for 'tasks' in the drop down code generator….Also would love some more posts on c#

  2. Matt Thalman says:


    The list of methods in the drop-down are the methods available that the developer can implement if they choose.  Selecting Task_Created from the drop-down will automatically generate the method stub and navigate you to the code file for the Task table.  From there, you just write your code.

  3. jeremy says:

    Hi Matt , thanks for your speedy response, however, i am not seeing the 'task' method listed under General methods, i am using lightswitch with Visual web dev 2010 , could that be an issue?, not sure why i'm not seeing the methos listed..

  4. Matt Thalman says:


    It's named Task_Created because the name of my table is Task.  LightSwitch names these methods based on the name of the table.  So if you had a table named "Foo", you'd see a bunch of methods prefixed with "Foo_".  The important part, in this case, is that you want to write code for the "Created" method.  This is the method that is invoked when the instance is first created.

  5. jeremy says:

    Thanks Matt, some times we write manuals/Instructions  for Pro's forgetting that newbees will also read,my understanding is that Lightswitch is aimed at the 'non-programmers market.just wanted to ask some questions others reaading may be afraid to ask and do not want to appear dumb :<) all the very best!.

  6. adefwebserver says:

    This blog post (and the blog) is invaluable. I also appreciate the design of the extensibility points in LightSwitch. It is brilliant.

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