使表ID成为自己的外键实体框架

Question

I wanted to know if it was possible to create a table with an id, a label and a foreign key referring to the id of the table itself. Below is the example of what I would like to do but that does not work because the public virtual RubricFo can not be called by itself.

public class RubricFO
{
   [Key, Required]
   public int IdRubricFO { get; set; }

   [MaxLength(250)]
   public string LabelRubricFO { get; set; }

   public bool IsActif { get; set; }

   public int RankDisplay { get; set; }

   [ForeignKey("IdRubricFO")]
   public int IdRubricFO_Fk { get; set; }
   public virtual RubricFO RubricFO { get; set; }

   public int IdStructure { get; set; }

   [ForeignKey("IdStructure")]
   public virtual Structures Structures { get; set; }
}

I do not know if I am clear enough if you need additional info do not hesitate to ask.

Answer 1

Yes, it is possible. You see this if you want a Tree structure, where every node of the Tree has zero or more SubNodes , no ParentNode if it is a top node, or one ParentNode if it is a SubNode .

class Node
{
    public int Id {get; set;}

    // every Node has zero or more subNodes:
    public virtual ICollection<Node> SubNodes {get; set;}

    // every Node is the subNode of zero or one ParentNode, using foreign key
    public int? ParentId {get; set;}         // null if it is a Top Node
    public virtual Node Parent {get; set;}
}

I'm pretty sure, that this is enough information for entity framework to understand the relations.

If not, you can use fluent API in your DbContext to inform entity framework about the model

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
     // build table Nodes:
     modelBuilder.Entity<Node>()
         .HasKey(node => node.Id)                // not needed, I followed the conventions
         .HasOptional(node => node.Parent)       // every node table has an optional Parent
         .WithMany(node => node.SubNodes)        // every Parent Node has zero or more SubNodes
         .HasForeignKey(node => node.ParentId);  // the foreign key to the parent node

Nice exercise: try int ParentId instead of int? , a zero value could mean there is no parent.