Stop fixing up to Deleted entities

[qslcna]

By reading this post relationship-changes. In many-to-many relationships, I consider when removing join entities PostTags from post.PostTags the removed entity will also disapper from tag.PostTags

If query tags before ctx.ChangeTracker.DetectChanges() it performs as expected.

However call ctx.ChangeTracker.DetectChanges() before query tags, the tag{id=2}'s navigation property PostTags still has {PostId: 1, TagId: 2} which state is deleted.

It dosen't disapper although I call ctx.ChangeTracker.DetectChanges() again

how to make DetectChanges has consistent result, no matter what order of invocation.

Entitis

using System.Collections.Generic;

namespace Web.Tests
{
    public class Post
    {
        public int Id { get; set; }
        public string Title { get; set; }
        public string Content { get; set; }

        public IList<PostTag> PostTags { get; } = new List<PostTag>(); // Collection navigation
    }

    public class Tag
    {
        public int Id { get; set; }
        public string Text { get; set; }

        public IList<PostTag> PostTags { get; } = new List<PostTag>(); // Collection navigation
    }

    public class PostTag
    {
        public int PostId { get; set; } // First part of composite PK; FK to Post
        public int TagId { get; set; } // Second part of composite PK; FK to Tag

        public Post Post { get; set; } // Reference navigation
        public Tag Tag { get; set; } // Reference navigation
    }
}

using Microsoft.EntityFrameworkCore;

namespace Web.Tests
{
    public class BlogContext : DbContext
    {
        public BlogContext(DbContextOptions<BlogContext> options) : base(options) { }

        public DbSet<Post> Posts { get; set; }
        public DbSet<Tag> Tags { get; set; }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Post>()
                .HasData(
                    new Post { Id = 1, Title = "How to use vs?", Content = "blababa" }
                );

            modelBuilder.Entity<Tag>()
                .HasData(
                    new Tag { Id = 1, Text = ".NET" },
                    new Tag { Id = 2, Text = "C#" }

                );
            modelBuilder.Entity<PostTag>()
                .HasKey(x => new { x.PostId, x.TagId });

            modelBuilder.Entity<PostTag>()
                .HasOne(x => x.Post)
                .WithMany(x => x.PostTags);

            modelBuilder.Entity<PostTag>()
                .HasOne(x => x.Tag)
                .WithMany(x => x.PostTags);

            modelBuilder.Entity<PostTag>()
                .HasData(
                    new PostTag { PostId = 1, TagId = 1 },
                    new PostTag { PostId = 1, TagId = 2 }
                );

            base.OnModelCreating(modelBuilder);
        }
    }
}

UnitTest1.cs

        [Fact]
        public void Test1()
        {
            var ctx = CreateContext();
            var post = ctx.Posts.Include(x => x.PostTags).SingleOrDefault(x => x.Id == 1);
            if (post != null)
            {
                post.PostTags.RemoveAt(1);
            }

            
            ctx.ChangeTracker.DetectChanges();
            Debug.WriteLine(ctx.ChangeTracker.DebugView.LongView);

            var tag = ctx.Tags.Include(x => x.PostTags).ToList();
            Debug.WriteLine(ctx.ChangeTracker.DebugView.LongView);

            ctx.ChangeTracker.DetectChanges();
            Debug.WriteLine(ctx.ChangeTracker.DebugView.LongView);


            ctx.SaveChanges();
        }

 Post {Id: 1} Unchanged
   Id: 1 PK
   Content: 'blababa'
   Title: 'How to use vs?'
   PostTags: [{PostId: 1, TagId: 1}]
 PostTag {PostId: 1, TagId: 1} Unchanged
   PostId: 1 PK FK
   TagId: 1 PK FK
   Post: {Id: 1}
   Tag: <null>
 PostTag {PostId: 1, TagId: 2} Deleted
   PostId: 1 PK FK
   TagId: 2 PK FK
   Post: <null>
   Tag: <null>

 Post {Id: 1} Unchanged
   Id: 1 PK
   Content: 'blababa'
   Title: 'How to use vs?'
   PostTags: [{PostId: 1, TagId: 1}]
 PostTag {PostId: 1, TagId: 1} Unchanged
   PostId: 1 PK FK
   TagId: 1 PK FK
   Post: {Id: 1}
   Tag: {Id: 1}
 PostTag {PostId: 1, TagId: 2} Deleted
   PostId: 1 PK FK
   TagId: 2 PK FK
   Post: <null>
   Tag: {Id: 2}
 Tag {Id: 1} Unchanged
   Id: 1 PK
   Text: '.NET'
   PostTags: [{PostId: 1, TagId: 1}]
 Tag {Id: 2} Unchanged
   Id: 2 PK
   Text: 'C#'
   PostTags: [{PostId: 1, TagId: 2}]

Post {Id: 1} Unchanged
  Id: 1 PK
  Content: 'blababa'
  Title: 'How to use vs?'
  PostTags: [{PostId: 1, TagId: 1}]
PostTag {PostId: 1, TagId: 1} Unchanged
  PostId: 1 PK FK
  TagId: 1 PK FK
  Post: {Id: 1}
  Tag: {Id: 1}
PostTag {PostId: 1, TagId: 2} Deleted
  PostId: 1 PK FK
  TagId: 2 PK FK
  Post: <null>
  Tag: {Id: 2}
Tag {Id: 1} Unchanged
  Id: 1 PK
  Text: '.NET'
  PostTags: [{PostId: 1, TagId: 1}]
Tag {Id: 2} Unchanged
  Id: 2 PK
  Text: 'C#'
  PostTags: [{PostId: 1, TagId: 2}]

Include provider and version information

EF Core version:5.0.12
Database provider: Pomelo.EntityFrameworkCore.MySql
Target framework:NET 5.0
Operating system:
IDE: vscode latest

[ajcvickers]

@qslcna EF Core 5.0 is no longer supported. Please update to EF Core 6.0 and report back if yo are still seeing the issue.

[qslcna]

@ajcvickers I tried EF Core 6.0.6. It has same issue.

[qslcna]

I want achive like this.

        [Fact]
        public void Test1()
        {
            var ctx = CreateContext();
            var post = ctx.Posts.Include(x => x.PostTags).SingleOrDefault(x => x.Id == 1);
            if (post != null)
            {
                post.PostTags.RemoveAt(1);
            }

            //ctx.ChangeTracker.DetectChanges();
            //Debug.WriteLine(ctx.ChangeTracker.DebugView.LongView);

           // But In my real project. I call  _context.ChangeTracker.Entries here. Which will trigger DetectChanges.

            var tag = ctx.Tags.Include(x => x.PostTags).ToList();
            Debug.WriteLine(ctx.ChangeTracker.DebugView.LongView);

            ctx.ChangeTracker.DetectChanges();
            Debug.WriteLine(ctx.ChangeTracker.DebugView.LongView);


            ctx.SaveChanges();
        }

Post {Id: 1} Unchanged
  Id: 1 PK
  Content: 'blababa'
  Title: 'How to use vs?'
  PostTags: [{PostId: 1, TagId: 1}]
PostTag {PostId: 1, TagId: 1} Unchanged
  PostId: 1 PK FK
  TagId: 1 PK FK
  Post: {Id: 1}
  Tag: {Id: 1}
PostTag {PostId: 1, TagId: 2} Unchanged
  PostId: 1 PK FK
  TagId: 2 PK FK
  Post: {Id: 1}
  Tag: {Id: 2}
Tag {Id: 1} Unchanged
  Id: 1 PK
  Text: '.NET'
  PostTags: [{PostId: 1, TagId: 1}]
Tag {Id: 2} Unchanged
  Id: 2 PK
  Text: 'C#'
  PostTags: [{PostId: 1, TagId: 2}]

 Post {Id: 1} Unchanged
  Id: 1 PK
  Content: 'blababa'
  Title: 'How to use vs?'
  PostTags: [{PostId: 1, TagId: 1}]
PostTag {PostId: 1, TagId: 1} Unchanged
  PostId: 1 PK FK
  TagId: 1 PK FK
  Post: {Id: 1}
  Tag: {Id: 1}
PostTag {PostId: 1, TagId: 2} Deleted
  PostId: 1 PK FK
  TagId: 2 PK FK
  Post: <null>
  Tag: {Id: 2}
Tag {Id: 1} Unchanged
  Id: 1 PK
  Text: '.NET'
  PostTags: [{PostId: 1, TagId: 1}]
Tag {Id: 2} Unchanged
  Id: 2 PK
  Text: 'C#'
  PostTags: []               // this is the point.

[ajcvickers]

Note for triage: EF is fixing up navigations to Deleted entities when queries are executed. I think there are cases where this is desirable, but it'll take some investigation for me to remember.

[qslcna]

@ajcvickers EF always fixing up added entities. why it behaves differently when handle deleted entities?

[qslcna]

@ajcvickers How is the investigation?

[ajcvickers]

@qslcna Are you saying that you want fixup to Deleted entities happen or not happen when a query is executed?

[qslcna]

@ajcvickers I want it happend. The point is in many to many relationship, remove form post navigation property post.PostTags.
it should fix up tag navigation property tag.PostTags after I query tags or after I query tags call DetectChanges manually.

[ajcvickers]

@qslcna You need to call DetectChanges after manipulating the collection, otherwise EF doesn't know that the collection has changed and that the entity should be marked as Deleted. In the code you posted originally this call was present, and I thought you were suggesting that fixup to Deleted entities should not occur, since conceptually, they are no longer in the graph.

See the docs on change detection: https://docs.microsoft.com/en-us/ef/core/change-tracking/change-detection

[qslcna]

I'm confused for the meaning of fixup now.
For example,

      var post = ctx.Posts.Include(x => x.PostTags).SingleOrDefault(x => x.Id == 1);
      if (post != null)
      {
          post.PostTags.RemoveAt(1);
      }

I removed PostTag {PostId: 1, TagId: 2}

Then I query tags;

    var tag = ctx.Tags.Include(x => x.PostTags).ToList();

tag.PostTags should not contain the entity I removed.

In this scenario fix up happend or not?

[ajcvickers]

You need to call DetectChanges after calling post.PostTags.RemoveAt(1);.

[qslcna]

Please check the original code (at the top of page). I did that. But the result of query tags still has the entity PostTag {PostId: 1, TagId: 2} which state already mark as deleted. And I want the tag.PostTags should have no PostTags which state is Deleted.

[qslcna]

Have I made it clear?

[qslcna]

I thought you were suggesting that fixup to Deleted entities should not occur, since conceptually, they are no longer in the graph.

Yes if deleted entities no longer in the graph, it should disapper form any navigation collections.

[qslcna]

@ajcvickers the fisrt part ( description about my question ) of original post has updated. Anxiously waiting for your reply. I've been struggling with this issue for a long time

[ajcvickers]

@qslcna Currently, executing a query causes the queried entities to be connected to any related Deleted entities, and vice-versa. I agree that this may not be the desired behavior. This is something we will investigate. However, that investigation will happen in due course as part of our normal work.

[qslcna]

 public class Receipt
    {
        public DateTime Date { get; set; }
        public int? CustomerId { get; set; }
        public int? SupplierId { get; set; }
        public decimal Total { get; set; }

        public virtual Customer Customer { get; set; }
        public virtual Supplier Supplier { get; set; }

        public virtual List<WriteOff> WriteOffs { get; set; }
    }

    public class SaleOut
    {
        public DateTime Date { get; set; }
        public int? CustomerId { get; set; }
        public int? SupplierId { get; set; }

        public decimal Total { get; private set; }
        public decimal Progress { get; private set; }

        public virtual Supplier Supplier { get; set; }
        public virtual Customer Customer { get; set; }

        public virtual List<SaleOutItem> Items { get; set; }

        public virtual List<WriteOff> WriteOffs { get; private set; }

        public void WriteOff()
        {
            var writeOffsTotal = this.WriteOffs.Sum(x => x.Amount);
            if (writeOffsTotal < 0 || writeOffsTotal > this.Total)
            {
                throw new Exception();
            }
            this.Progress = writeOffsTotal;
        }
    }

    public class WriteOff
    {

        public decimal Amount { get; set; }

        public int TradeId { get; set; }
        public int OwnerId { get; set; }

        public virtual SaleOut Trade { get; set; }
        public virtual Receipt Owner { get; set; }
    }

Consider the situation， If Receipt.WriteOffs modified. I need update related SaleOut.Progress.

1. I got those SaleOut ids by _context.ChangeTracker.Entries<WriteOff>().Select(x => x.Entity.TradeId);
2. query thouse SaleOuts by ids form step 1, and invoke SaleOut.WriteOff() form each result.

if the query result still connected to Deleted Entities the Progress will not be right. BTW add WirteOff works fine. the SaleOut query result will always connected to Added Entities.

Do you have any advice on this.

[ajcvickers]

@qslcna I'm afraid I find it very hard to understand the details of what you are trying to do, and hence don't really have any advice.

[panjonsen]

It has an endless loop, and its ideal result is the same as "Teacher=null", because I have no Include.
@ajcvickers