Broken code for saving a graph of entities

[litoj]

Type of issue

Code doesn't work

Description

I am trying to save a graph just like in the example shown. But there are multiple issues with the example:

• whatever I do, it throws an error when saving the Post, because the executed INSERT has still BlogId=0
• providing the Blog to the Post didn't help
• using Sync/Async processing didn't change anything
• the Post has many objects that are expected to be not null, yet aren't required to be set in constructor - this generates compilator warnings

Page URL

https://learn.microsoft.com/en-us/ef/core/saving/related-data#adding-a-graph-of-new-entities

Content source URL

https://github.com/dotnet/EntityFramework.Docs/blob/main/entity-framework/core/saving/related-data.md

Document Version Independent Id

c7517e7d-f011-a24c-53da-913771913998

Article author

@ajcvickers

[timdeschryver]

I tried to reproduce this, and I initially received the following error

Microsoft.Data.SqlClient.SqlException (0x80131904): Cannot insert the value NULL into column 'Content', table 'EFDocs.dbo.Posts'; column does not allow nulls. UPDATE fails.

This occurs because I created a new project with Nullable reference types enabled. Reading the comment "this generates compilator warnings", I expect this is also the case for you.

To fix the example, either remove the <Nullable>enable</Nullable> config in your csproj file, or set the content of the posts.

using (var context = new BloggingContext())
{
    var blog = new Blog
    {
        Url = "http://blogs.msdn.com/dotnet",
        Posts = new List<Post>
        {
            new Post { Title = "Intro to C#", Content = string.Empty},
            new Post { Title = "Intro to VB.NET", Content = ""},
            new Post { Title = "Intro to F#", Content = "Intro to F#"},
        }
    };

    context.Blogs.Add(blog);
    context.SaveChanges();
}

If wanted, I can update the docs by assigning a value to the content properties.

[litoj]

The primary issue is rather that there is no clarification what happens with the post.BlogId - does it just magically figure out it is from the object above? Also that part in particular did not work for me - I wasn't able to save it like that and instead it always threw an error about breaking FK constraint - precisely because the posts didn't get the BlogId set.

[timdeschryver]

@litoj it's normal that the entity has id 0, during the insert it should receive the appropriate id.
For example, with Sql Server the Id column will be the Primary Key, which is auto incremented ([BlogId] [int] IDENTITY(1,1) NOT NULL)

[litoj]

Yes, but how does the post.BlogId get set? Because in my tests it didn't and that's why I got the errors.

[timdeschryver]

Sorry @litoj , I don't know - normally, that should also work automatically.