EF Core 2.1：具有一对多关系的自引用实体会生成其他列 [英] EF Core 2.1: Self-referencing entity with one to many relationship generates additional column

问题描述

我有以下实体：

public class Level
{
    public int LevelId { get; set; }
    public int? ParentLevelId { get; set; }
    public string Name { get; set; }

    public virtual Level Parent { get; set; }
    public virtual HashSet<Level> Children { get; set; }   
}

我在这里遇到的麻烦是子项属性，在Fluent API中进行如下配置：

What I am having trouble here, is the Children property, which is configured like this in Fluent API:

modelBuilder.Entity<Level>()
    .HasOne(x => x.Parent)
    .WithMany(x => x.Children)
    .HasForeignKey(x => x.ParentLevelId);

这会导致迁移添加了其他列：

This results in some additional column being added by the migration:

migrationBuilder.AddColumn<int>(
    name: "LevelId1",
    table: "Level",
    nullable: true);

migrationBuilder.CreateIndex(
    name: "IX_Level_LevelId1",
    table: "Level",
    column: "LevelId1");

migrationBuilder.AddForeignKey(
    name: "FK_Level_Level_LevelId1",
    table: "Level",
    column: "LevelId1",
    principalTable: "Level",
    principalColumn: "LevelId",
    onDelete: ReferentialAction.Restrict);

我在这里做什么错了？

编辑：该问题被标记为此问题的可能重复项；但是，在这种情况下，模型生成有效-问题在于加载数据。而在这里，问题在于生成了另外一列。

Question was marked as a possible duplicate of this question; however, in that case, the model generation works - the issue is loading the data. Whereas here, the issue is that an additional column is generated.

推荐答案

迁移过程中有些混乱。初始化该模型时不进行复制：

Something's messed up in your migration. No repro when initializing that model:

using Microsoft.EntityFrameworkCore;
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;

namespace EfCoreTest
{

    public class Level
    {
        public int LevelId { get; set; }
        public int? ParentLevelId { get; set; }
        public string Name { get; set; }

        public virtual Level Parent { get; set; }
        public virtual HashSet<Level> Children { get; set; }
    }

    public class Db : DbContext
    {
        public DbSet<Level> levels { get; set; }


        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseSqlServer("server=.;database=EfCoreTest;Integrated Security=true");
            base.OnConfiguring(optionsBuilder);
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            base.OnModelCreating(modelBuilder);
            modelBuilder.Entity<Level>()
                        .HasOne(x => x.Parent)
                        .WithMany(x => x.Children)
                        .HasForeignKey(x => x.ParentLevelId);

        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            using (var db = new Db())
            {
                db.Database.EnsureDeleted();
                db.Database.EnsureCreated();

                Console.ReadKey();



            }

        }
    }
}

创建表：

CREATE TABLE [levels] (
    [LevelId] int NOT NULL IDENTITY,
    [ParentLevelId] int NULL,
    [Name] nvarchar(max) NULL,
    CONSTRAINT [PK_levels] PRIMARY KEY ([LevelId]),
    CONSTRAINT [FK_levels_levels_ParentLevelId] FOREIGN KEY ([ParentLevelId]) REFERENCES [levels] ([LevelId]) ON DELETE NO ACTION
);

添加了迁移，

PM> Add-Migration InitialCreate

仍然没有复制项：

using Microsoft.EntityFrameworkCore.Metadata;
using Microsoft.EntityFrameworkCore.Migrations;

namespace EfCoreTest.Migrations
{
    public partial class InitialCreate : Migration
    {
        protected override void Up(MigrationBuilder migrationBuilder)
        {
            migrationBuilder.CreateTable(
                name: "levels",
                columns: table => new
                {
                    LevelId = table.Column<int>(nullable: false)
                        .Annotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn),
                    ParentLevelId = table.Column<int>(nullable: true),
                    Name = table.Column<string>(nullable: true)
                },
                constraints: table =>
                {
                    table.PrimaryKey("PK_levels", x => x.LevelId);
                    table.ForeignKey(
                        name: "FK_levels_levels_ParentLevelId",
                        column: x => x.ParentLevelId,
                        principalTable: "levels",
                        principalColumn: "LevelId",
                        onDelete: ReferentialAction.Restrict);
                });

            migrationBuilder.CreateIndex(
                name: "IX_levels_ParentLevelId",
                table: "levels",
                column: "ParentLevelId");
        }

        protected override void Down(MigrationBuilder migrationBuilder)
        {
            migrationBuilder.DropTable(
                name: "levels");
        }
    }
}

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