Error "EntityType has no key defined" for composite keys - ef-code-first

Question

I am trying to bind my data using entity framework v6.1.3 but I am getting this error message EntityType has no key defined. Define the key for this EntityType. (I am having a composite key)
I've tried the following approaches:
public class CommunicationCollection
{
[Key, Column(Order = 0)]
[ForeignKey("FK_CommunicationCollection_Communication")]
public Guid CommunicationId;
[Key, Column(Order = 1)]
[ForeignKey("FK_CommunicationCollection_Collection")]
public Guid CollectionId;
}
and this
public class CommunicationCollection
{
[Key, Column(Order = 0)]
[ForeignKey("FK_CommunicationCollection_Communication")]
public Guid CommunicationId;
[Key, Column(Order = 1)]
[ForeignKey("FK_CommunicationCollection_Collection")]
public Guid CollectionId;
public virtual Communication Communication { get; set; }
public virtual Collection Collection { get; set; }
}
and also this
public class CommunicationCollection
{
[Key, Column(Order = 0)]
public Guid CommunicationId;
[Key, Column(Order = 1)]
public Guid CollectionId;
}
and in the DB I have
CREATE TABLE [CommunicationCollection](
[CommunicationId] [uniqueidentifier] NOT NULL,
[CollectionId] [uniqueidentifier] NOT NULL,
CONSTRAINT [PK_CommunicationCollection] PRIMARY KEY CLUSTERED
(
[CommunicationId] ASC,
[CollectionId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, FILLFACTOR = 80) ON [PRIMARY]
) ON [PRIMARY]
GO
ALTER TABLE [CommunicationCollection] WITH CHECK ADD CONSTRAINT [FK_CommunicationCollection_Collection] FOREIGN KEY([CollectionId])
REFERENCES [Collection] ([CollectionId])
GO
ALTER TABLE [CommunicationCollection] CHECK CONSTRAINT [FK_CommunicationCollection_Collection]
GO
ALTER TABLE [CommunicationCollection] WITH CHECK ADD CONSTRAINT [FK_CommunicationCollection_Communication] FOREIGN KEY([CommunicationId])
REFERENCES [Communication] ([CommunicationId])
GO
ALTER TABLE [CommunicationCollection] CHECK CONSTRAINT [FK_CommunicationCollection_Communication]
GO
Any idea what am I missing?
Thanks a lot!

Answer 1

With EF, everything needs to be properties and not just 'plain' variables. This is needed so EF can hook into those methods.
So like this:
public Guid CommunicationId { get; set; }
public Guid CollectionId { get; set; }
Forgetting to do this causes all kinds of problems that can be hard to trace back to the actual cause, as you have just encountered.