CodeFirst EF4.1 MVC Against legacy database - Multiplicity conflicts

Hope this is still on time to help you. I was also having the exact same problem and was troubling with it for almost an hour until I could spot my mistake.

The problem is that Course.Venue relationship is optional (as declared on the fluent API), but the Id declaration of Course.VenueId is mandatory, so you can either make VenueId optional by changing it to

public int? VenueId { get; set;}

or change the relationship to mandatory on the fluent API, and the OnModelCreating should run fine once you changed that.

After searching the web for

System.Data.Edm.EdmAssociationType: : Multiplicity conflicts with the referential constraint in Role

It kept comming up with this post so here was my problem and solution:

I upgraded a large project from ef4.0 to ef4.1 using the vs ef reverse engineering extension. Our mvc app was using metadatatype and partials to decorate ef4.0 objects.

After removing the files of the metadatatype the project began working.

The root problem was [Required] attribute as ef poco object had nullable and my metadatatype had [Required] on the same property. Previously was to enforce mvc validation rules and now ef4.1 was using to populate navigation properties. Removing [Required] off metadatatype fixed the problem.

public partial class AgentAgency
{
    public long OID { get; set; }
    public long? AgentOID { get; set; }
    public long? AgencyOID { get; set; }
    public string ReinsuranceYear { get; set; }
    public virtual Agency Agency { get; set; }
    public virtual Agent Agent { get; set; }
}

public class AgentAgencyMetadata
{
    public Int64 OID { get; set; }

    [Required]
    public Int64 AgentOID { get; set; }

    [Required]
    public Int64 AgencyOID { get; set; }
}