Jul 17

Written by: Michael Washington
7/17/2011 9:54 AM 

The following is an excerpt from the E-Book: “Creating Visual Studio LightSwitch Custom Controls (Beginner to Intermediate)”

 

You will find a slight problem with the chart in the preceding chapter. If a sales person does not have any sales for a quarter, they will not appear on the chart at all.

In Sales Quarter 2, all three sales people have sales, therefore each sales person appears on the chart.

However, delete the 2^nd quarter sales for Mary (remember to click save).

When we return to the Sales By Quarter page (and click Refresh to update the data with the latest changes), we see that Mary is entirely absent from the chart for that sales quarter.

LightSwitch is designed to require you to create each new record you want, as a new record. Only then can you represent the data on the screen. We have a screen that shows the sales data for the second quarter. Mary has no sales, so Mary does not show.

What we sometimes desire, is for LightSwitch to create “blank spots”. We would like to see Mary on the chart (but with sales of 0).

While this scenario is not exclusive to Silverlight Custom Controls, it will most likely come up, because, when you are creating Silverlight Custom Controls, you want the screen to appear exactly how you desire.

First, Get All the Data You Need On The Screen

This first step is not obvious. You will need to place all the collections you will need on the screen, even if you do not plan to show all the collections on the screen.

However, remember that by default all collections are set to only contain 45 records at a time. You will want to turn paging off, in the Properties for the collection, if you need to access all records in a collection programmatically.

To resolve our particular challenge, we need to determine what sales people do not have sales data for the selected quarter. This requires us to query the SalesPerson entity, and the sales of each person to see if they have sales for the selected quarter.

Currently we have the SalesByQuarter query on the screen. The problem with just using this query, is that it has already filtered the sales people, to only those sales people that have sales for the quarter.

We need a collection that provides access to all the sales people.

Add the SalesPerson (All) collection to the screen.

We now have programmatic access to the collection.

Again, remember that by default this collection will only contain 45 records. You will want to turn off paging, in the Properties for the collection, to have programmatic access to all the records.

Create In-Memory Records

The next step is to wire-up a method to fire whenever the SaleQuarter parameter is changed.

Click on the SaleQuarter parameter in the View Model for the screen, and then select SaleQuarter changed to create the method.

 

   int intLastSalesQuarter = -1;
    partial void SaleQuarter_Changed()
    {
        // Check to see if the Quarter actually changed to prevent looping
        if (intLastSalesQuarter != this.SaleQuarter)
        {
            intLastSalesQuarter = this.SaleQuarter;
            // Remove any unsaved Sales                
            foreach (Sale sale in this.DataWorkspace.ApplicationData.Details.GetChanges()
                .AddedEntities.OfType<Sale>())
            {
                sale.Details.DiscardChanges();
            }
            // Get all SalesPersons who do not have Sales for the Quarter
            int[] intSalesPersonsWithoutSales = (from objSalesPersons in SalesPersons
                                                    where objSalesPersons.Sales.
                                                    FirstOrDefault(x => x.SaleQuarter 
                                                        == SaleQuarter) == null
                                                    select objSalesPersons.Id).ToArray();
            int intTempID = -1;
            // Loop through the SalePersons
            foreach (int item in intSalesPersonsWithoutSales)
            {
                // Get the SalesPerson record
                SalesPerson objSalesPerson = 
                    DataWorkspace.ApplicationData.SalesPersons_Single(item);
                // Create a Sale for the SalesPerson
                Sale objSale = objSalesPerson.Sales.AddNew();
                objSale.Sales = 0;
                objSale.SaleQuarter = SaleQuarter;
                objSale.SalesPerson = objSalesPerson;
                // We need to give each record a unique ID 
                // So we insert negative numbers and count backwards
                objSale.Id = intTempID;
                intTempID--;
            }
        }
    }

 

Change the code to the code above.

Now, when you run the application, Mary will show on the chart, even though she has no sales for the selected sale quarter.

 

Download Code

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

It is the “ChartViewer” sample under Creating Visual Studio LightSwitch Custom Controls (Beginner to Intermediate) (E-Book)