Storing graph with EF Code First

问题

I'm trying to save a graph into a database as described here with EF Code First.

I defined property with collection of adjacent nodes:

public class Node {
    public int NodeId { get; set; }
    public string NodeName { get; set; }
    public ICollection<Node> Nodes { get; set; }
}

but EF generated only one table for this model:

dbo.Nodes
    NodeId (PK, int, not null)
    NodeName (nvarchar(max), null)
    Node_NodeId (FK, int, null)

How to force EF to generate many-to-many relationship?

Are there any other ways to store graphs in the database?

回答1:

Your class model expresses that a Node has one collection of nodes, which can be fully accommodated by the generated table. If you want many-to-many, you'll have to tell EF about your plans.

One thing you can do is make parent and child collections:

public class Node
{
    public int Id { get; set; }
    public string NodeName { get; set; }
    public ICollection<Node> ParentNodes { get; set; }
    public ICollection<Node> ChildNodes { get; set; }
}

EF will create a join table as follows:

[dbo].[NodeNodes]
    [Node_Id] [int] NOT NULL,
    [Node_Id1] [int] NOT NULL

If you want more meaningful names of the columns you could do this:

class NodeContext : DbContext
{
    public DbSet<Node> Nodes { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);

        modelBuilder.Entity<Node>()
            .HasMany(n => n.ParentNodes)
            .WithMany(n => n.ChildNodes)
            .Map(c => c.MapLeftKey("ChildNodeId")
                .MapRightKey("ParentNodeId"));
    }
}

Try this:

var root = new Node { NodeName = "Root" };
root.ParentNodes = new List<Node> { new Node { NodeName = "Par1" }, new Node { NodeName = "Par2" } };
root.ChildNodes = new List<Node> { new Node { NodeName = "Ch1" }, new Node { NodeName = "Ch2" } };
con.Nodes.Add(root);
con.SaveChanges();

(Where con is a NodeContext instance) and see if you like the result.

来源：https://stackoverflow.com/questions/9653861/storing-graph-with-ef-code-first

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entity-framework

entity-framework-4