实体框架返回“ $ ref”项目

Question

I'm doing my homework - making an web api 2 project with entity framework.

Here is my table layout, with m-2-m relationship between Singer and Genre tables.

My Genre is a table which I Use to get my singers list by alphabet (so Genre table get data from (ID: 1, Name: "A") to (ID: 26, Name: "Z")

Now I want to get all singers start with "H" (id=8)

public IQueryable<Singer> GetByGenre(int id)
    {            
        return db.Singers.Where(s => s.Genres.Any(g => g.ID == id));
    }

with this query:

http://localhost:6798/api/Singers/GetByGenre?id=8

But the result's strange - only the first result's show, while others return as "ref" ? I checked by create a "fake" list

var list = db.Singers.Where(s => s.Genres.Any(g => g.ID == id)).ToList();

and put debug on it, and it return correct 3 Singers ?

--

And as you see, I have other table (Song, Playlist, Video) which have a FK point to ID of my Singer , so how can I only return the Singer table's columns only (ID, NAME, IMAGE) without all other relationship data ( Playlists, Songs, Videos ...) ?

Answer 1

Why does it include $ref in returned json result.

It is Json serializer who is including $ref to resolve the circular dependancies.

Look here for detail on this Stackoverflow answer -> Why is the Web Api returning empty json results with “$ref=”?

how can I only return the Singer table's columns only (ID, NAME, IMAGE) without all other relationship data ( Playlists, Songs, Videos ...) ?

You need to disable your lazy loading in the entity framework dbcontext.

something like this way:

db.Configuration.LazyLoadingEnabled = false;

For more information about lazy loading and serializer have a detailed look at this msdn article.