EF代码优先-定义双向导航属性

Question

I have this entity class

public class Node
{
    [Key]
    public int Id { get; private set; }
    public string Name { get; set; }
    public virtual Node Prev { get; set; }
    public virtual Node Next { get; set; }
}

A node will always have 0 or 1 previous node and 0 or 1 next node.

And I would like EF to generate the following table schema

Id | Name | Prev_Id | Next_Id

As you will soon notice that, Next_Id is redundant since Prev_Id is sufficient to define the directional relationship.

My purpose of this table schema is to efficiently query whether a node has a previous / next node without doing a join operation on its own table. And I am happy to take the trade-off that I have to write extra logic to maintain the prev/next id correctness.

Here is my problem:

The EF fails to create such table with the following error:

Unable to determine the principal end of an association between the types 'Node' and 'Node'. The principal end of this association must be explicitly configured using either the relationship fluent API or data annotations.

I wonder if EF allows such design and how.

UPDATES

I change to this and still got the same error

public class Node
{
    [Key]
    public int Id { get; private set; }
    public string Name { get; set; }
    public int PrevId { get; set; }
    public int NextId { get; set; }
    [ForeignKey("PrevId")]
    public virtual Node Prev { get; set; }
    [ForeignKey("NextId")]
    public virtual Node Next { get; set; }
}

Answer 1

I don't think you can do this. Consider re-design your table schema. Let's say I want to add 3 new nodes like following:

var first = new Node { Name = "first" };
var second = new Node { Name = "second" };
var third = new Node { Name = "third" };

first.Next = second;
second.Prev = first;
second.Next = third;
third.Prev = second;

---- expected table data ----
Id       Name         PrevId        NextId
1        first         NULL           2
2        second         1             3
3        third          2            NULL

Now you tell me which row should be inserted first. If the id=1 row is inserted first, it breaks the foreign key constraint because NextId=2 doesn't exist. Similarly id=2 & id=3 rows can't be inserted first.

Maybe you can remove the foreign key constraint and manage the relationship by yourself in the code, or using store procedures.