Cannot create a DbSet for 'Model' because this type is not included in the model for the context.

Hi!

We recently updated EF Core from 2.0.2 to 2.1.2, and this code that worked perfectly fine earlier, has now started failing with some strange errors. When debugging this code in Visual Studio 2017, the error can not be reproduced. It only occurs when we have deployed this code to our Azure App Service.

We have a pretty basic Entity model that looks like this:

public class Model: IAudit
{
    [Key,
    DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public string Id { get; set; }

    [Required(ErrorMessage = "This field is required."),
    MaxLength(100, ErrorMessage = "This field may contain a maximum of {1} characters.")]
    public string Name { get; set; }

    public ICollection<AnotherModel> OherModels { get; set; }

    public DateTime Created { get; set; }
    public DateTime Updated { get; set; }
    public DateTime? Deleted { get; set; }
}

And in our DbContext, our OnModelCreating method looks like this:

public DbSet<Model> Model { get; set; }


protected override void OnModelCreating(ModelBuilder builder)
{
    base.OnModelCreating(builder);

     builder.Entity<Model>()
        .HasIndex(o => new { o.Name, o.App })
            .HasName("QueryAndSort");

    builder.Entity<Model>()
        .HasIndex(o => new { o.Deleted })
        .HasFilter("[Deleted] IS NULL")
        .HasName("NotDeleted");

    builder.Entity<AnotherModel>()
        .HasOne(o => o.Model)
        .WithMany(o => o.OherModels)
        .HasForeignKey(o => o.ModelId)
        .IsRequired()
        .OnDelete(DeleteBehavior.Restrict);

    builder.Entity<Model>();

    ...
}

We then run the following code to get the entity from the database:

return _context.Set<Model>()
    .AsNoTracking()
    .Where(o => o.Name == name)
    .ToList();

Since upgrading to 2.1.2 This now throws the following exception:

Exception message: Cannot create a DbSet for 'Model' because this type is not included in the model for the context.
Stack trace:
System.InvalidOperationException:
   at Microsoft.EntityFrameworkCore.Internal.InternalDbSet`1.get_EntityType (Microsoft.EntityFrameworkCore, Version=2.1.2.0, Culture=neutral, PublicKeyToken=adb9793829ddae60)
   at Microsoft.EntityFrameworkCore.Internal.InternalDbSet`1.get_EntityQueryable (Microsoft.EntityFrameworkCore, Version=2.1.2.0, Culture=neutral, PublicKeyToken=adb9793829ddae60)
   at Microsoft.EntityFrameworkCore.Internal.InternalDbSet`1.System.Linq.IQueryable.get_Provider (Microsoft.EntityFrameworkCore, Version=2.1.2.0, Culture=neutral, PublicKeyToken=adb9793829ddae60)
   at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.Include (Microsoft.EntityFrameworkCore, Version=2.1.2.0, Culture=neutral, PublicKeyToken=adb9793829ddae60)
   at Project.Data.DAL.ModelRepository+<>c__DisplayClass6_0.<GetCached>b__0 (Project.Data, Version=1.0.0.0, Culture=neutral, PublicKeyToken=Project.Data, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null: C:\projects\Project.Data\DAL\ModelRepository.cs, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null: 49)

Strangely, all other entities in the project can be fetched with no problems, and we can also get the Model items from the database by including them in another query such as the one:

return _context.Set<AnotherModel>()
    .Include(o => o.Model)
    .FirstOrDefault(o => o.Id == id);

Further technical details

EF Core version: 2.1.2 Database Provider: Microsoft.EntityFrameworkCore.SqlServer Operating system: Windows at Azure App Service