Saving a graph of entities doesn't work for depth greater than 1

### 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