C#•5mo ago

Breaking a cycle (Post > Blog > Post > Blog > ...)

Hey fellows! I stumbled into a cycle and don't know how to break it. It occurs between posts and blogs. This is the controller action:

[HttpPost("/blog/{blogSlug}/post")]
    public async Task<Post> CreatePost([FromBody] PostInput postInput, [FromRoute] string blogSlug)
    {
        User user = await _dataContext.Users.FirstAsync((u) => u.Slug == "timo");
        Blog blog = await _dataContext.Blogs.FirstAsync((b) => b.Slug == blogSlug);
        Post newPost = PostMapper.ToPost(postInput, user: user, blog: blog);
        _dataContext.Posts.Add(newPost);
        await _dataContext.SaveChangesAsync();

        return newPost;
    }

[HttpPost("/blog/{blogSlug}/post")]
    public async Task<Post> CreatePost([FromBody] PostInput postInput, [FromRoute] string blogSlug)
    {
        User user = await _dataContext.Users.FirstAsync((u) => u.Slug == "timo");
        Blog blog = await _dataContext.Blogs.FirstAsync((b) => b.Slug == blogSlug);
        Post newPost = PostMapper.ToPost(postInput, user: user, blog: blog);
        _dataContext.Posts.Add(newPost);
        await _dataContext.SaveChangesAsync();

        return newPost;
    }

How to break the cycle? Thanks.

20 Replies

Angius•5mo ago

.Select() Instead of fetching everything from a user, and everything from a blog, select only what's needed Not sure what PostMapper.ToPost() does

Timo Martinson•5mo ago

public class PostMapper
{
    public static Post ToPost(PostInput postInput, User user, Blog blog)
    {
        return new Post(name: postInput.Name, slug: postInput.Slug, content: postInput.Content, user: user, blog: blog);
    }
}

public class PostMapper
{
    public static Post ToPost(PostInput postInput, User user, Blog blog)
    {
        return new Post(name: postInput.Name, slug: postInput.Slug, content: postInput.Content, user: user, blog: blog);
    }
}

Angius•5mo ago

Not sure what would cause a cycle here, tbh Do you have lazy loading enabled, with vitual properties or something? Also, are you using the built-in Identity for users, or did you build your own system? If the former, you should probably just get the user ID from claims and use that to create the post, instead of getting the user from the database By a hardcoded name, no less

Timo Martinson•5mo ago

the hardcoded name was just for testing purposes this is the error message:

System.Text.Json.JsonException: A possible object cycle was detected. This can either be due to a cycle or if the object depth is larger than the maximum allowed depth of 32. Consider using ReferenceHandler.Preserve on JsonSerializerOptions to support cycles. Path: $.Blog.Posts.Blog.Posts.Blog.Posts.Blog.Posts.Blog.Posts.Blog.Posts.Blog.Posts.Blog.Posts.Blog.Posts.Blog.Posts.Id.

System.Text.Json.JsonException: A possible object cycle was detected. This can either be due to a cycle or if the object depth is larger than the maximum allowed depth of 32. Consider using ReferenceHandler.Preserve on JsonSerializerOptions to support cycles. Path: $.Blog.Posts.Blog.Posts.Blog.Posts.Blog.Posts.Blog.Posts.Blog.Posts.Blog.Posts.Blog.Posts.Blog.Posts.Blog.Posts.Id.

when accessing all post-routes: /blog/.../post

Angius•5mo ago

You want to return data in a form that doesn't cause cycles, then Use a DTO

Timo Martinson•5mo ago

I am using them already.

Angius•5mo ago

For the input Not for the output

Timo Martinson•5mo ago

aaaha how would you approach it ?

Angius•5mo ago

I probably wouldn't be returning the blogpost back, just an Ok if it was created succesfully, Unauthorized if user cannot be found, and NotFound if the blog is not foud Alternatively, I would return a CreatedAtAction() Othwerwise... just make a DTO

  [HttpPost("/blog/{blogSlug}/post")]
- public async Task<Post> CreatePost([FromBody] PostInput postInput, [FromRoute] string blogSlug)
+ public async Task<PostDto> CreatePost([FromBody] PostInput postInput, [FromRoute] string blogSlug)****
  {
      User user = await _dataContext.Users.FirstAsync((u) => u.Slug == "timo");
      Blog blog = await _dataContext.Blogs.FirstAsync((b) => b.Slug == blogSlug);
      Post newPost = PostMapper.ToPost(postInput, user: user, blog: blog);
      _dataContext.Posts.Add(newPost);
      await _dataContext.SaveChangesAsync();

-      return newPost;
+      return new PostDto {
+          Title = newPost.Title,
+          Slug = newPost.Slug,
+          // ...
+      };
  }

  [HttpPost("/blog/{blogSlug}/post")]
- public async Task<Post> CreatePost([FromBody] PostInput postInput, [FromRoute] string blogSlug)
+ public async Task<PostDto> CreatePost([FromBody] PostInput postInput, [FromRoute] string blogSlug)****
  {
      User user = await _dataContext.Users.FirstAsync((u) => u.Slug == "timo");
      Blog blog = await _dataContext.Blogs.FirstAsync((b) => b.Slug == blogSlug);
      Post newPost = PostMapper.ToPost(postInput, user: user, blog: blog);
      _dataContext.Posts.Add(newPost);
      await _dataContext.SaveChangesAsync();

-      return newPost;
+      return new PostDto {
+          Title = newPost.Title,
+          Slug = newPost.Slug,
+          // ...
+      };
  }

Timo Martinson•5mo ago

ah ok nice @ZZZZZZZZZZZZZZZZZZZZZZZZZ could you provide me a snippet that shows how to use required props instead of constructors? Just as you pointed out, yesterday.

Angius•5mo ago

You use them just like normal properties, with initializer syntax

public class Foo
{
    public required string Bar { get; init; }
}

var f = new Foo {
    Bar = "unga bunga"
};

public class Foo
{
    public required string Bar { get; init; }
}

var f = new Foo {
    Bar = "unga bunga"
};

Timo Martinson•5mo ago

nice thank you and what's the story behind "init" ?

Angius•5mo ago

It can only be set in the initializer or constructor, and cannot be changed after Essentially, immutability

public class Foo
{
    public required string Bar { get; init; }
    public required string Baz { get; set; }
}

var f = new Foo {
    Bar = "unga bunga",
    Baz = "foo bar",
};

f.Bar = "abc"; // not allowed
f.Baz = "abc"; // allowed

public class Foo
{
    public required string Bar { get; init; }
    public required string Baz { get; set; }
}

var f = new Foo {
    Bar = "unga bunga",
    Baz = "foo bar",
};

f.Bar = "abc"; // not allowed
f.Baz = "abc"; // allowed

Timo Martinson•5mo ago

and you skip the constructor stuff entirely? if I want to use Entity Framework ?

Angius•5mo ago

As you can see in the example, no constructor was needed

Timo Martinson•5mo ago

cool

MODiX•5mo ago

Angius

REPL Result: Success

public class Foo
{
    public required string Bar { get; init; }
    public required string Baz { get; set; }
}

var f = new Foo {
    Bar = "unga bunga",
    Baz = "foo bar",
};

f

public class Foo
{
    public required string Bar { get; init; }
    public required string Baz { get; set; }
}

var f = new Foo {
    Bar = "unga bunga",
    Baz = "foo bar",
};

f

Result: Foo

{
  "bar": "unga bunga",
  "baz": "foo bar"
}

{
  "bar": "unga bunga",
  "baz": "foo bar"
}

Compile: 312.851ms | Execution: 44.459ms | React with ❌ to remove this embed.

Timo Martinson•5mo ago

good how does it work with Entity Framework?

Angius•5mo ago

It just does™ EF just uses reflections to set the properties

Timo Martinson•5mo ago

good

Gaming

Programming

Breaking a cycle (Post > Blog > Post > Blog > ...)