one-zero-one relation ef codefrist

我有3个class

public class StockDef
{
    public int Id { get; set; }
    public int StockType { get; set; }
    public virtual OfficeStock SayanStock { get; set; }
    public virtual AgentStock AgentStock { get; set; }
    //....
}
public class OfficeStock
{
    public virtual StockDef StockDef { get; set; }
    //....
}
public class AgentStock
{
    public virtual StockDef StockDef { get; set; }
    //......
}

每个StockDef对象肯定有(一个OfficeStock或一个AgentStock)。每个OfficeStock都有一个StockDef。
每个AgentStock绝对有一个StockDef。
我如何实现这一点，在EF代码首先通过流畅的API?
tnx