Multiplicity conflicts with the referential constraint

Question

I'm receiving the following EF error:

Agent_MailingAddress: : Multiplicity conflicts with the referential constraint in Role 'Agent_MailingAddress_Target' in relationship 'Agent_MailingAddress'. Because all of the properties in the Dependent Role are non-nullable, multiplicity of the Principal Role must be 1

It appears to throw this when it executes base.OnModelCreating(modelBuilder).

Here are my models. FWIW, Agent inherits from a User class.

public class Agent
{
    public int AgentId { get; set; }
    public int PrimaryAddressId { get; set; }
    public Address PrimaryAddress { get; set; }
    public int? MailingAddressId { get; set; }
    public Address MailingAddress { get; set; }
}

public class Address
{
    public int AddressId { get; set; }
    public string AddressLine1 { get; set; }
    public string AddressLine2 { get; set; }
}

I believe the issue has something to do with the fact that Agent has more than one property of type Address and possibly also because one of them is nullable. I've done some searching, but can't seem to find an answer.

I assume altering my Agent model to have a single property of type List<Address> that would use a UserAddresses lookup table would resolve the error, but I would prefer to keep the current model and not.

How can I resolve this error? Thanks in advance.

Answer 1

This can happen if your configuration and your model do not match.

Let's say in your db configuration you have a rule like this:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Entity<Agent>().HasRequired(x=>x.MailingAddress);
    //..

But in your model you say that MailingAddress is optional:

public int? MailingAddressId { get; set; }

I believe the issue has something to do with the fact that Agent has more than one property of type Address and possibly also because one of them is nullable

It's not the case.

Answer 2

For database first: if you altered an existing table already added to Entity Framework, say added a foreign key constraint after the fact, delete the table in the EDMX designer and add again and this will resolve the error.

Answer 3

Another way to determine the root of the problem is the following :

1. open the .edmx file and find the entity containing the foreign key field.
2. find the property that is causing the error message and right click to open the context menu.
3. click properties on the context Menu to open the properties window.
4. Examine the Nullable property for the field and change it to the appropriate value.