Elastic scale query with EF: Nullable object must have a value - entity-framework

Question

On Azure, I have a setup of several sharded databases and an elastic query database with external tables mirroring the tables on the shards. The two main tables I use are:
Channels:
[Name] nvarchar NOT NULL,
[Id] [uniqueidentifier] NOT NULL,
[ExternalReference] nvarchar NULL
Users:
[Email] nvarchar NOT NULL,
[FirstName] nvarchar NOT NULL,
[LastName] nvarchar NOT NULL,
[ChannelId] [uniqueidentifier] NOT NULL,
[Status] [int] NOT NULL,
[AvatarId] [uniqueidentifier] NULL,
[Id] [uniqueidentifier] NOT NULL
When I query this via EF and linq:
var user = db.Users.Include("Channel").FirstOrDefault(u => u.Email ==
"tony#soprano.com");
I get an error:
An error occurred while executing GlobalQuery operation: Nullable object must have a value.
This is what the User class looks like:
public class User
{
public Guid Id { get; set; } = SequentialGuid.NewGuid();
[Required]
public string Email { get; set; }
[Required]
public string FirstName { get; set; }
[Required]
public string LastName { get; set; }
[Index]
public Status Status { get; set; }
public Guid? AvatarId { get; set; }
[Index]
public Guid ChannelId { get; set; }
[ForeignKey("ChannelId")]
public virtual Channel Channel { get; set; }
}
Querying directly via T-SQL:
SELECT * FROM Users INNER JOIN Channels ON Users.ChannelId = Channels.Id
gives me the same error.
Further investigation shows that casting the Ids to uniqueidentifiers (which they already are) solves the problem:
SELECT * FROM Users INNER JOIN Channels ON CAST(Users.ChannelId as uniqueidentifier) = CAST(Channels.Id as uniqueidentifier)
The ChannelId and Id Columns are already non nullable uniqueidentifiers. The data inside the shards is also valid and not null, so what exactly is the problem here?
Another question: how can I force that ‘cast to uniqueidentifier’ in linq?

Answer 1

Quick question, you state that "Querying directly via T-SQL:
SELECT * FROM Users INNER JOIN Channels ON Users.ChannelId = Channels.Id
gives me the same error." , are you querying from the Elastic Query Head database, or on a shard? I setup the schema and could not repro when querying from the shard, so I am wondering if I am not repro'ing the issue correctly?