Aug 20

Written by: Michael Washington
8/20/2011 10:37 AM 

LightSwitch is a powerful application builder when you use WCF RIA Services and Silverlight Custom Controls (or Silverlight Control Extensions). Otherwise, it is merely just a fast and easy application builder. In order to be fast and easy, LightSwitch has it’s limitations. However, when you employ WCF RIA Services and Silverlight Custom Controls, you are able to overcome any limitations.

When you use WCF RIA Services and Silverlight Custom Controls, there is nothing that LightSwitch cannot do, that you could do with a normal Silverlight application. The http://LightSwitchHelpWebsite.com site has a number of articles on Silverlight Custom Controls, this article will concentrate on WCF RIA Services.

Note: You must have Visual Studio Professional (or higher) to create WCF RIA Services using the method described in this article.

 

Why You Need WCF RIA Services

Let’s say you have this requirement:

Show the latest status for the warehouse (where the order is being placed)

This may not seem like a difficult requirement, except when the status for each warehouse is in a different table, and each table has a different structure. LightSwitch is able to handle this situation, just place each Entity (table) on the screen using a Tab Control, and allow the user to switch between the Tabs.

With a little programming, you may be able to automatically switch between the Tabs based on the order being viewed. This solution, like many “out-of-the-box” LightSwitch solutions, eats up a lot of “screen real estate” (also, if you have a lot of warehouses you would eventually run out of room on the screen).

Furthermore, a big complex user interface is difficult for users to learn, and time-consuming to use, because the users have to switch between screens and Tab containers.

An optimal solution is to simply show the status of the warehouse as the order is being placed…

 

The LightSwitch Application

We create a new LightSwitch application.

 

We create two different Entities (tables) to hold the status of each warehouse. Notice they have different structures. In the “real world” we are faced with situations like this (perhaps each warehouse uses a different application to report their status).

Yes we could create a SQL Server View to tie the two Entities together, but a WCF RIA Service will also allow you to update the data if you needed to.

 

When we complete the application, the user is able to manually switch tabs to see the status for the warehouses. However, what if there were dozens of warehouses?

 

The WCF RIA Service

We follow the directions, to create a WCF RIA Service, in this article: WCF RIA Service: Combining Two Tables.

We use this class to return the results:

 

    public class WarehouseStatus
    {
        [Key]
        public int ID { get; set; }
        [Key]
        public string Warehouse { get; set; }
        public string StatusMessage { get; set; }
        public DateTime EffectiveDate { get; set; }
    }

 

(notice that two fields are marked [Key] because LightSwitch needs to know what fields comprise a unique key for each record)

We must have a method that returns the collection that does not take parameters:

 

        [Query(IsDefault = true)]
        public IQueryable<WarehouseStatus> GetAllStatusMessages()
        {
            var colNorthWarehouses = from NorthWarehouses in this.Context.NorthWarehouses
                                     select new WarehouseStatus
                                     {
                                         ID = NorthWarehouses.Id,                                         
                                         Warehouse = "North",
                                         StatusMessage = NorthWarehouses.Status,
                                         EffectiveDate = NorthWarehouses.EntryDate
                                     };
            var colSouthWarehouses = from SouthWarehouses in this.Context.SouthWarehouses
                                     select new WarehouseStatus
                                     {
                                         ID = SouthWarehouses.Id,                                         
                                         Warehouse = "South",
                                         StatusMessage = SouthWarehouses.StatusMessage,
                                         EffectiveDate = SouthWarehouses.EffectiveDate
                                     };
            return colNorthWarehouses.Union(colSouthWarehouses).AsQueryable();
        }

 

Yes this method could also be called by normal LightSwitch code that uses normal Linq queries, however, we will demonstrate how to make a method that takes a parameter for those cases where you must have a method that takes a parameter, such as when the method calls a stored procedure.

The following is the method that takes a parameter:

 

        public IQueryable<WarehouseStatus> GetAllStatusByWarehouse(string Warehouse)
        {
            var colWarehouses = from Warehouses in GetAllStatusMessages()
                                where Warehouses.Warehouse == Warehouse
                                select Warehouses;
    
            return colWarehouses;
        }

 

 

Note, you also need to add the following method for any paging of the collections to work:

 

        // Override the Count method in order for paging to work correctly
        protected override int Count<T>(IQueryable<T> query)
        {
            return query.Count();
        }

 

First, we build the WCF RIA Service project (ignore any warnings you may see in the output window).

Next, we add the new Data Source.

 

We select WCF RIA Service.

 

We Add Reference.

 

We select the WCF_RIA_Project.

 

Note, you may have to wait up to a minute for the Service Class to display in the list box.

 

Select the collection and click Finish.

 

The Entity (table) will display.

 

It will also display in the Solution Explorer. Also note that the method that takes a parameter (GetAllStatusByWarehouse) also displays.

LightSwitch treats the GetAllStatusByWarehouse method as it would any other Pre-process Query, the only difference is that you cannot edit it in the normal LightSwitch editor (you must alter the code in the method in the WCF RIA project).

 

On the Screen we can Add Data Item…

 

… and select the GetAllStatusByWarehouse collection.

 

When it is added to the Screen’s collection (the Screen’s View Model), it indicates that it has a parameter that must be supplied.

 

We can click on the parameter and in the properties for the parameter, bind it to the SelectedItem in the Orders collection.

 

We select the Warehouse field.

 

We can also edit the query for the GetAllStatusByWarehouse collection…

 

… and set the Sort.

We could also set additional parameters to constrain the query. At this level, LightSwitch treats this data source as it would any other Entity.

 

When we run the application, we now have a user interface that will automatically show the status for the proper warehouse.

 

WCF RIA Services Are Part Of LightSwitch

If you avoid using WCF RIA Services with LightSwitch, it would be like buying a sports car and never going past 3rd gear. LightSwitch was designed to be used with WCF RIA Services. This is what allows LightSwitch to be used for professional applications.

You may decide, “I will just use FindControl(“MyTabControl”) and automatically switch Tabs”. The problem you will face, is that if there are any errors, you will not find them until the application is running (meaning you may never find them, your end-users will). If you use the methods described here, any errors will show up at “compile time”  (meaning the application will not run and it will show you exactly where any errors are).

In addition, the methods described here require LESS code than it would if you used another method.

 

Further Reading

WCF RIA Service: Combining Two Tables

Creating a Simple LightSwitch RIA Service (using POCO)

Saving Files To File System With LightSwitch (Uploading Files)

Using WCF RIA Services to connect to LightSwitch Security:

How to reference security entities in LightSwitch

Linking LightSwitch Data to Logged in Users

 

Download Code

The LightSwitch project is available at http://lightswitchhelpwebsite.com/Downloads.aspx