EF多对多删除无法正常工作

Question

I've checked in at least 20 different places about how to delete a many-to-many registry using Entity Framework, and my code seems to be working according to almost all solutions I found. Unfortunately, I can't delete the relationship, no matter what. Here's the code:

using (var db = new Context())
{                
    var project = db.Projects.Single(p => p.Id == "myId");

    foreach (var toRemove in project.Orders.Where(o =>
                                     ordersToRemove.Select(otr => otr.Id).Contains(o.Id)).ToList())
    {
         project.Orders.Remove(toRemove);

    }
    db.SaveChanges();
}

I also tried to force the removal inside the "foreach", getting the order from "db" and removing the Project relationship from it, just to test, but it was useless.

As a matter of information, I've debugged it and my Orders collection inside project had the Orders removed correctly right before "SaveChanges".

In the same code I have a very similar flow to add orders to Project and it works fine.

I did the mapping in Context manually, like this:

modelBuilder.Entity<Project>()
            .HasMany(p => p.Orders)
            .WithMany(o => o.Projects)
            .Map(pc =>
            {
                pc.MapLeftKey("ProjectId");
                pc.MapRightKey("OrderId");
                pc.ToTable("Projects_Orders");
            });

I believe it's something silly that I can't figure out, so because of it I ask your help. Sorry if it's a duplicated question, but like I said before, I found a lot of answers that the code is pretty the same as mine.

UPDATED: I found out someone which had the same issue as me ( here ), and I tried to use the marked solution, but didn't work. I also tried to clear all collection, then save, and then add again the orders that should remain, and didn't work either. Another solution was to create an entity for the related table (something like ProjectOrder), but I thought it would be too damn ugly.

In the end, I used "executesqlcommand" - and I'm not proud of it . I just couldn't waste more time in it, unfortunately.

Answer 1

UPDATED : Previous answer was reflecting how to delete One-Many, here is an updated sample that I tried and I am able to delete Many-To-Many relationship without any issues. Please ignore the naming convention as I put this together real quick for testing purpose.

ORDER Entity

namespace TestEF6.Data
{
    using System.Collections.Generic;
    using System.ComponentModel.DataAnnotations;
    using System.ComponentModel.DataAnnotations.Schema;

    [Table("ORDER")]
    public partial class ORDER
    {
        public ORDER()
        {
            PROJECTS = new HashSet<PROJECT>();
        }

        [Key]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int ID { get; set; }

        [StringLength(50)]
        public string NAME { get; set; }

        public virtual ICollection<PROJECT> PROJECTS { get; set; }
    }
}

PROJECT entity

namespace TestEF6.Data
{
    using System.Collections.Generic;
    using System.ComponentModel.DataAnnotations;
    using System.ComponentModel.DataAnnotations.Schema;

    [Table("PROJECT")]
    public partial class PROJECT
    {
        public PROJECT()
        {
            ORDERS = new HashSet<ORDER>();
        }

        [Key]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int ID { get; set; }

        [StringLength(50)]
        public string NAME { get; set; }

        public virtual ICollection<ORDER> ORDERS { get; set; }
    }
}

Context class

namespace TestEF6.Data
{
    using System;
    using System.Data.Entity;

    public partial class ProjectManagerContext : DbContext
    {
        public ProjectManagerContext()
            : base("name=ProjectManager")
        {
        }

        public virtual DbSet<ORDER> ORDERs { get; set; }
        public virtual DbSet<PROJECT> PROJECTs { get; set; }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            Database.Log = Console.WriteLine;

            modelBuilder.Entity<PROJECT>()
            .HasMany(p => p.ORDERS)
            .WithMany(o => o.PROJECTS)
            .Map(pc =>
            {
                pc.MapLeftKey("PROJECT_ID");
                pc.MapRightKey("ORDER_ID");
                pc.ToTable("PROJECT_ORDER");
            });
        }
    }
}

UNIT TESTS

using System.Diagnostics;
using System.Linq;
using NUnit.Framework;

namespace TestEF6.Data.Tests
{
    [TestFixture]
    public class ProjectOrderTests
    {
        [Test]
        public void Can_Remove_Projects_And_Orders_Relation()
        {
            using (var db = new ProjectManagerContext())
            {
                var proj1 = db.PROJECTs.Single(p => p.NAME == "TEST PROJ 1");

                Debug.WriteLine($"Num of proj1 orders = [{proj1.ORDERS.Count}]");
                foreach (var order in proj1.ORDERS.ToList())
                {
                    Debug.WriteLine($"Removed proj order = [{proj1.NAME}] [{order.NAME}]");
                    proj1.ORDERS.Remove(order);

                }

                db.SaveChanges();
            }
        }

        [Test]
        public void Can_Add_Projects_And_Orders()
        {
            using (var db = new ProjectManagerContext())
            {
                var proj1 = new PROJECT { NAME = "TEST PROJ 1" };
                var proj2 = new PROJECT { NAME = "TEST PROJ 2" };
                var proj3 = new PROJECT { NAME = "TEST PROJ 3" };
                db.PROJECTs.Add(proj1);
                db.PROJECTs.Add(proj2);
                db.PROJECTs.Add(proj3);
                db.SaveChanges();

                var order1 = new ORDER { NAME = "ORDER 1" };
                var order2 = new ORDER { NAME = "ORDER 2" };

                db.ORDERs.Add(order1);
                db.ORDERs.Add(order2);
                db.SaveChanges();

                proj1.ORDERS.Add(order1);
                proj1.ORDERS.Add(order2);
                proj2.ORDERS.Add(order2);

                db.SaveChanges();
            }
        }


    }
}

Here is config file

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <configSections>
    <!-- For more information on Entity Framework configuration, visit http://go.microsoft.com/fwlink/?LinkID=237468 -->
    <section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
  </configSections>
  <entityFramework>
    <defaultConnectionFactory type="System.Data.Entity.Infrastructure.LocalDbConnectionFactory, EntityFramework">
      <parameters>
        <parameter value="mssqllocaldb" />
      </parameters>
    </defaultConnectionFactory>
    <providers>
      <provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
    </providers>
  </entityFramework>
  <connectionStrings>
    <add name="ProjectManager" connectionString="data source=MYTESTSQL2014;initial catalog=ProjectManagerDb;user id=test_user;password=test$pwd!;MultipleActiveResultSets=True;App=EntityFramework" providerName="System.Data.SqlClient" />
  </connectionStrings>
</configuration>

Here is how the table structure in SQL server is defined and the join table foreign key columns are set to Allow nulls.

Test Results

There were 3 rows in PROJECT_ORDER table before deletion

There is just one row after the delete