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Creating Computed Columns In Light Switch 2011

In this tutorial I will explain about how to create computed columns in Lightswitch.

Software Requirement

Before you start reading this tutorial you should make sure that

Visual studio 2010 is installed on your machine.
Visual Studio 2010 service pack 1 is installed on your machine.
Microsoft Visual Studio Light switch 2011 is installed on your machine.

Prerequisite Knowledge

Before you go ahead, it is required that you should know

What is lightswitch?
What are screens and entities in lightswitch?
How to create an entity in lightswitch?
How to create a screen in lightswitch?

What Are Computed Columns?

Computed columns are those whose value is calculated from other field (or fields) based on some calculation.

Creation Of Person Entity

Picture showing the Person lightswitch table

Click to Enlarge

In the above entity I have added 2 columns PersonName and Age. Now let’s add computed column in this entity.

Add Computed Column In Person Entity

In this entity I will create a computed column which sets the flag based on the age of person. The requirement is if the person’s age is lesser than 18 then he (or she) is not eligible for voting else he (or she) can vote.

First of all click on the Computed Property button as highlighted in the image below.

Picture showing adding the computed property in the table

Click to Enlarge

Once you click on it a column is added in the entity as shown in the figure above. Right now the name of the column is Property1, but we can change it by clicking on column and type new name. One thing to notice here is the icon before Property1. This icon shows that the value in the column will be calculated on the basis of some calculation (as mentioned in the definition).

In the figure below I have renamed the column from Property1 to IsEligibleToVote and change its data type from string to Boolean.

Picture showing adding the IsEligibleToVote computed column in the table

Click to Enlarge

Add Logic For Computed Column

In this section I will show you what would be the logic of the computed column. For writing the logic

Select the column by single click on the column (IsEligibleToVote in this case).
On the property window click on the Edit Method link.
Code screen comes.

Picture showing the edit method for writing the code in the computed column

Click to Enlarge

In the figure below the logic is written in the code - if the Age is lesser than 18 then the person is not eligible for vote else he (or she) is eligible for vote.

Picture showing the code window for writing the code for the computed column

Click to Enlarge

Creation Of Editable Grid Screen

To add a new screen right click on the Screens folder in Solution Explorer and click Add Screen…

Once you click on Add Screen… a popup appears. Select all the options as shown in figure below and click Ok.

Picture showing selecting the Editable Grid Screen from the Add Screen window

Click to Enlarge

Create A New Record

Click to Enlarge

When the user clicks Plus (+) button, a popup window comes. As you can see in the figure above IsEligbleToVote field is true when there is no value entered in age. When the user enters value then field changes see the figure below.

Click to Enlarge

Enter details and click Ok.

Output

Click to Enlarge

Posted By -	Karan Gupta

Posted On -	Monday, April 2, 2012

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