Part 14 Conditional Mapping in entity framework

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In this video we will discuss Conditional Mapping feature in entity framework with database first approach. Let us understand what Conditional Mapping can do with an example.

We will be using Employees table in this demo. IsTerminated column determines if an employee is a terminated employee or not.

If the application that we are developing always need only the employees who are not terminated, then in the query we will have to always include the filter across our entire application. Conditional Mapping can be used to apply such a permanent filter on the entity, so that the generated SQL query always have the WHERE clause.

To use Conditional Mapping,
1. Right click on the entity and select "Table Mapping" option from the context menu
2. Add the condition - When Is Terminated = false

At this point, if you build or validate the model, you will get the following error
Problem in mapping fragments starting at line 46:Condition member 'Employees.IsTerminated' with a condition other than 'IsNull=False' is mapped. Either remove the condition on Employees.IsTerminated or remove it from the mapping

This is because, a table column cannot be mapped more than once. We have used IsTerminated column in conditional mapping, so it cannot be used in property mapping as well. For this reason delete it from Employee entity.

Add a web form to the project. Drag and drop a GridView control. Copy and paste the following code in the code-behind file.
protected void Page_Load(object sender, EventArgs e)
{
EmployeeDBContext employeeDBContext = new EmployeeDBContext();
GridView1.DataSource = employeeDBContext.Employees.ToList();
GridView1.DataBind();
}

Open SQL profiler and run the webform. Notice that the select query has a where clause, which will always return employees who are not terminated.
SELECT
[Extent1].[EmployeeID] AS [EmployeeID],
[Extent1].[FirstName] AS [FirstName],
[Extent1].[LastName] AS [LastName],
[Extent1].[Gender] AS [Gender]
FROM [dbo].[Employees] AS [Extent1]
WHERE [Extent1].[IsTerminated] = 0