使用EF代码首先存储图 [英] Storing graph with EF Code First

问题描述

我试图将图形保存到数据库中，如此处与EF代码首先。

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

我用相邻节点的集合定义属性：

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; }
}

但EF只为此模型生成了一个表：

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)

如何强制EF生成多对多关系？

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

有没有其他方法可以在数据库中存储图形？

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

推荐答案

您的类模型表示 Node 具有一个节点集合，可以由生成的表完全容纳。如果你想要多对多，你必须告诉EF你的计划。

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.

你可以做的一件事是做父母和孩子的集合：

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将创建一个连接表，如下所示：

EF will create a join table as follows:

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

如果您想要更有意义的列名称，您可以这样做：

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"));
    }
}

尝试这个：

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();

（其中 con 是一个 NodeContext 实例），看看你喜欢的结果。

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

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