实体框架Core中的多对一映射

Question

I have a User class

public partial class User
{
    public int Id { get; set; }
    public string UserName { get; set; }
    public virtual ICollection<Blog> Blogs { get; set; }
}

and this is my Blog class

public partial class Blog
{
    public int Id { get; set; }
    public string Title { get; set; }
    public string Content { get; set; }
    public int? PostedBy { get; set; }
    public virtual User { get; set; }
    public virtual ICollection<BlogImage> BlogImages { get; set; }
}

and my Image class

public partial class BlogImage
{
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual Blog Blog { get; set; }
}

I need to select from Blog with image Name and UserName

I've created this query but I don't now how to join the User class:

var blog = _context.Blog.Include(x => x.BlogImage).Include(a => a.BlogImage).ToListAsync();

Answer 1

Try -

var blog = await _context.Blog
    .Select(p => new
    {
        Id = p.Id,
        Title = p.Title,
        Content = p.Content,
        PostedBy = p.PostedBy,
        UserName = p.User.UserName,
        ImageNames = p.BlogImages.Select(x => x.Name).ToList()
    })
    .ToListAsync();

You can also create a DTO type to hold the result you are expecting -

public class BlogDTO
{
    public int Id { get; set; }
    public string Title { get; set; }
    public string Content { get; set; }
    public int? PostedBy { get; set; }

    public string UserName { get; set; }
    public List<string> ImageNames { get; set; }
}

and then query like -

BlogDTO blogDTO = await _context.Blog
        .Select(p => new BlogDTO
        {
            Id = p.Id,
            Title = p.Title,
            Content = p.Content,
            PostedBy = p.PostedBy,
            UserName = p.User.UserName,
            ImageNames = p.BlogImages.Select(x => x.Name).ToList()
        })
        .ToListAsync();