EF4 code first many to many relationship to external entity

Question

Problem

I've got two classes:

• OfficeProfile: exists within my EF model
• BusinessUnit: comes from an external source, e.g. a web service

There is a many to many relationship between office profiles and business units, which I'd like to represent in a link table OfficeProfilesBusinessUnits. I don't want to end up with a BusinessUnits table however that contains a list of business units as these are stored in an external domain outside of my control.

Is it possible to achieve this?

public class OfficeProfile
{
    public OfficeProfile()
    {
        ContactNumbers = new HashSet<ContactNumber>();
        BusinessUnits = new HashSet<BusinessUnit>();
    }

    public int OfficeProfileId { get; set; }
    public Address Address { get; set; }
    public ICollection<ContactNumber> ContactNumbers { get; private set; }
    public ICollection<BusinessUnit> BusinessUnits { get; private set; }
}

public class BusinessUnit
{
    public BusinessUnit(string code, string name, BusinessUnit parent)
    {
        Code = code;
        Name = name;
        Parent = parent;
    }

    public string Code { get; set; }
    public string Name { get; set; }
    public BusinessUnit Parent { get; set; }
}

What I've tried

I've tried ignoring the BusinessUnit entity, however that omits the link table.

I've tried ignoring the BusinessUnit entity whilst mapping the many-to-many relationship, however that throws an InvalidOperationException stating

The navigation property 'BusinessUnits' is not a declared property on type 'OfficeProfile'. Verify that it has not been explicitly excluded from the model and that it is a valid navigation property

.

Answer 1

You could add an extra entity which would only have an ID and a link to the BusinessUnit. In your Entity Model you would then ignore the BusinessUnit but add the link entity so you get the many to many relation link table.