Cannot create more than one clustered index on tab

问题:

I am having the following error after typing update-database:

Cannot create more than one clustered index on table 'dbo.AppUsers'. Drop the existing clustered index 'PK_dbo.AppUsers' before creating another.

I am working on an Azure mobile service.

I have three data models:

public class AppUser : EntityData
{
    public string Username { get; set; }
    public virtual ICollection<RatingItem> userRatings { get; set; }
}

public class PlaceItem : EntityData
{
    public string PlaceName { get; set; }
    public int Group { get; set; }
    public string XCoordinate { get; set; }
    public string YCoordinate { get; set; }
}

public class RatingItem : EntityData
{
    public int Ratings { get; set; }
    public string PlaceId { get; set; }
    public AppUser user { get; set; }
}

It has to do with migration because :

• The initial create is in the _MigrationHistory table, but isn't in the migration folder in the solution explorer.
• When I add-migration AddAll, I don't get any errors, and AddAll appears in the migration folder, but not in the table.

In the context file:

public class ICbackendContext : DbContext
{
        public DbSet<AppUser> AppUsers { get; set; }
        public DbSet<PlaceItem> PlaceItems { get; set; }
        public DbSet<RatingItem> RatingItems { get; set; }

}

回答1:

Generally, this error message is caused by not running the Mobile Apps/Mobile Services DB generator. Entity Framework does not have an annotation for creating a clustered index that is not a primary key, so the mobile server SDK manually creates the right SQL statements to set CreatedAt as a non-primary key clustered index.

To resolve this, run the database generator before migrations are applied. In the Migrations\Configuration.cs file, include the following:

public Configuration()
{
   AutomaticMigrationsEnabled = false;
   SetSqlGenerator("System.Data.SqlClient", new EntityTableSqlGenerator());
}

To learn more, see How to make data model changes to a .NET backend mobile service. The topic applies to both Mobile Services and Mobile Apps, though some namespaces are different in Mobile Apps.

回答2:

As stated by @gorillapower in comments, this piece of code is also very important.

modelBuilder.Conventions.Add(new AttributeToColumnAnnotationConvention<TableColumnAttribute, string>( "ServiceTableColumn", (property, attributes) => attributes.Single().ColumnType.ToString()));

inside your

protected override void OnModelCreating(DbModelBuilder modelBuilder)

in the DbContext config class. Do not forget to regenerate migrations.