How to call ThenInclude twice in EF Core?

问题

I'm creating an ASP.NET Core API app, and relying on EF Core. I have entities defined like this:

public class AppUser : IdentityUser
{
    public string FirstName { get; set; }

    public string LastName { get; set; }

    [InverseProperty(nameof(Post.Author))]
    public ICollection<Post> Posts { get; set; } = new List<Post>();
}

public class Post
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int Id { get; set; }

    public string AuthorId { get; set; }

    [ForeignKey("AuthorId")]
    public virtual AppUser Author { get; set; }

    [InverseProperty(nameof(Like.Post))]
    public ICollection<Like> Likes { get; set; } = new List<Like>();

    [InverseProperty(nameof(Comment.Post))]
    public ICollection<Comment> Comments { get; set; } = new List<Comment>();
}

Where Comment and Like are some other entities. Please note that I have simplified the entities for brevity. Then, I want to get the Posts of a user, but also include the Likes and Comments that a post has gotten. So, I did something like this:

return _context.Users
               .Include(u => u.Location)
               .Include(u => u.Posts)
                    .ThenInclude(p => p.Comments)
                        .ThenInclude(c => c.Owner)
               .Include(u => u.Posts)
                    .ThenInclude(p => p.Likes)
                        .ThenInclude(l => l.Giver)
               .Where(u => u.Id == userId)
               .FirstOrDefault();

Now, this works fine, but as you can see I'm calling .Include(u = u.Posts) twice. Is there a way to call ThenInclude twice on same property, without actually writing the Include statement also twice?

回答1:

You cannot use ThenInclude with multiple navigation properties. You have to have Include.

Here is bug opened for this.

回答2:

Now, this works fine, but as you can see I'm calling .Include(u = u.Posts) twice. Is there a way to call ThenInclude twice on same property, without actually writing the Include statement also twice?

Calling Include(u => u.Posts) twice is the right way to do it.

From EF Core docs... emphasis on the last sentence.

You may want to include multiple related entities for one of the entities that is being included. For example, when querying Blogs, you include Posts and then want to include both the Author and Tags of the Posts. To do this, you need to specify each include path starting at the root. For example, Blog -> Posts -> Author and Blog -> Posts -> Tags. This does not mean you will get redundant joins, in most cases EF will consolidate the joins when generating SQL.

using (var context = new BloggingContext())
{
    var blogs = context.Blogs
        .Include(blog => blog.Posts)
            .ThenInclude(post => post.Author)
        .Include(blog => blog.Posts)
            .ThenInclude(post => post.Tags)
        .ToList();
}

来源：https://stackoverflow.com/questions/50897638/how-to-call-theninclude-twice-in-ef-core