If you are having a problem in filtering a many-to-many related data in your Microsoft Lightswitch project, don’t worry I have a simple solution for you. Here it goes.
Lets say you have a table structure like the one above and you want to filter off the Task (sysTask) of a chosen User (mstUser). As you can see, a User can have many Tasks while a Task can have many Users, it is a Many-to-Many related table so to speak. Many of the solutions to this problem in the Internet is of course through WCF RIA Service but I have a simpler way.
First. Make a query in your SysTask table as shown in the image below. Add a parameter only, in my example, the parameter is UserId, an Integer.
Second. Write a code in the PreprocessQuery.
Below is the sample code. Basically it is a complex LINQ code the counts the user’s task record based on the user screen table (mstUserScreen) a shown in the database diagram.
Private Sub SysTasksFiltered_PreprocessQuery(UserId As System.Nullable(Of Integer), ByRef query As System.Linq.IQueryable(Of LightSwitchApplication.sysTask)) query = From q In query Where q.sysScreen.mstUserScreens.Where(Function(u) u.mstUser.Id = UserId).Count() > 0 End Sub
Thats it! To use the query, just add it as a Data Property to your screen and tie up the parameter to any controls that contains the equivalent data, in our example it’s UserId.
Below is my sample screen in action.
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