c# - Mapping Database Views to EF 5.0 Code First w/Migrations

Question

I'm trying to map a SQL View to an entity in EF 5.0 Code First w/Migrations for displaying some basic information on a page without having to query multiple tables for that information (which currently takes ~20 seconds to load. NOT GOOD.). I've heard that it is possible to do, but I haven't been able to figure out or find online a way to properly do so.

EDIT: For a more in-depth look at my solution to this problem, read this blog post on the subject.

Here is my View:

CREATE VIEW [dbo].[ClientStatistics]
AS
SELECT       ROW_NUMBER() OVER (Order By c.ID) as Row, c.LegacyID, c.ID, c.ClientName, slc.AccountManager, slc.Network,
                             (SELECT        MAX(CreatedDate) AS Expr1
                               FROM            dbo.DataPeriods
                               WHERE        (ClientID = c.ID)) AS LastDataReceived,
                             (SELECT        MAX(ApprovedDate) AS Expr1
                               FROM            dbo.DataPeriods AS DataPeriods_2
                               WHERE        (ClientID = c.ID)) AS LastApproved,
                             (SELECT        MAX(ReportProcessedDate) AS Expr1
                               FROM            dbo.DataPeriods AS DataPeriods_1
                               WHERE        (ClientID = c.ID)) AS LastReportProcesssed
FROM            dbo.Clients AS c INNER JOIN
                         dbo.SLClients AS slc ON c.ID = slc.ClientID

Here is the entity:

public class ClientStatisticsView
{
    [Key]
    public int Row { get; set; }
    public int LegacyID { get; set; }
    public int ClientID { get; set; }
    public string ClientName { get; set; }
    public string AccountManager { get; set; }
    public string Network { get; set; }
    public DateTime LastDataReceived { get; set; }
    public DateTime LastApproved { get; set; }
    public DateTime LastReportProcessed { get; set; }
}

And finally my mapping in DbContext:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Conventions.Remove<OneToManyCascadeDeleteConvention>();

    modelBuilder.Entity<ClientStatisticsView>().ToTable("ClientStatistics");

    base.OnModelCreating(modelBuilder);
}

All of this gives me the following error:

There is already an object named 'ClientStatistics' in the database.

What am I doing wrong? Is there any way to me to accomplish this, or should I be doing something else instead?

Answer 1

You have specified that the ClientStatisticsView entity should be mapped to a table named "ClientStatistics". So entity framework will generate a migration containing an instruction to create that table. But you have independently created that view in the database so to prevent the error you are getting you should remove the CreateTable instruction from the Up migration.

I think a better way to do it is to create the view in the migration by running sql like this:

public override void Up()
{
    Sql("EXEC ('CREATE View [dbo].[ClientStatistics] AS --etc"
}

public override void Down()
{

    Sql(@"IF  EXISTS (SELECT
                        *
                    FROM sys.views
                    WHERE object_id = OBJECT_ID(N'dbo.ClientStatistics'))
                    DROP VIEW dbo.ClientStatistics)")
}

That way your views and tables are specified in one place and you can safely migrate up and down

Reference

http://elegantcode.com/2012/04/12/entity-framework-migrations-tips/