How to map custom class name to database table with Entity Framework

In earlier post, How to insert records in database using Entity Framework, I discussed how you can use code first approach to create a POCO (Plain old CLR object) and then use data context to manipulate the tables. In that example POCO name was one to one match with table names in the database. Entity Framework was able to map the table with class name without any problem.

But you will always have cases where table names will not match with class names. This will happen if you are trying to reuse some existing code where classes were created based on some older schema. But now you have database tables that have totally different names. Another example, which I will use in this discussion, is using ASP.Net membership provider tables and procedures. You will notice that each database table is prefixed with aspnet_ by default. Now if you have classes with named like aspnet_Applications in your project, it will violate all the coding standard constraints and policies. And if you have some TFS check-in policy in place then you are out of luck because all policies will be violated.

There is a simple solution to this problem. You can create your POCO names to comply with standard naming convention. For example in my application, I want to query aspnet_Applications table but I want to keep my class name as Application. Following code snipper shows how I defined my class.

using System.ComponentModel.DataAnnotations;

[Table("aspnet_Applications")]
public class Application
{
 public Guid ApplicationId { get; set; }
 public string ApplicationName { get; set; }
 public string Description { get; set; }
}

I added TableAttribute to the class and set the name of the actual database table to which this class maps to. To add this attribute you will need to include System.ComponentModel.DataAnnotations in your class file.

If you do not add this attribute, you will see an exception like below when trying to query data context for the objects from that table.

Invalid object name dbo.Application

You can follow the same approach to map data base fields to class properties that do not match one to one.