简单映射时的EF 5.0多重性错误

Question

我有以下域对象:

public class Person 
{
    public int Id {get; set;}
    public int? FatherId {get; set;}
    public int? MotherId {get; set;}
    public int? HomeChurchId {get; set;}
    public int? BirthCountryId {get; set;}

    public Parent Father {get; set;}
    public Parent Mother {get; set;}
    public Church HomeChurch {get; set;}
    public Country BirthCountry {get; set;}
}

public class Parent
{
    public int Id {get; set;}
    ...
}

public class Church
{
    public int Id {get; set;}
    ...
}

public class Country
{
    public int Id {get; set;}
    ...
}

映射Person时,所有这些属性的映射方式几乎相同:

HasOptional(p => p.Father).WithMany().HasForeignKey(p => p.FatherId);
HasOptional(p => p.BirthCountry).WithMany().HasForeignKey(p => p.BirthCountryId);    
...

问题是,使用BirthCountry,当我尝试查询Person时,我收到以下错误:

One or more validation errors were detected during model generation:

System.Data.Entity.Edm.EdmAssociationType: : Multiplicity conflicts with the
referential constraint in Role 'Person_BirthCountry_Target' in relationship
'Person_BirthCountry'. Because all of the properties in the Dependent Role are 
non-nullable, multiplicity of the Principal Role must be '1'.

如果我删除BirthCountry属性(和映射)一切正常.令我困惑的是,BirthCountry的设置就像Person中的其他所有可空属性一样.为什么其他属性没有给我同样的错误？

感谢您提供的任何帮助!

Answer 1

无知并不是幸福......它只是令人沮丧.

我终于意识到我在BirthCountryId上有一个[Required]属性.这导致了问题......这完全有道理.我无法告诉EF它的可选和同时需要.

希望这可以拯救别人免受同样的挫折感.