c# - 如何编写 linq 查询以在 mvc web 应用程序中获取 blogId

Question

我有 2 个模型:

public class Blog
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Url { get; set; }
    public string RealBlogId { get; set; }     
}

  public class Post
{
    public int Id { get; set; }
    public int? BlogId { get; set; }
    public string Title { get; set; }
    public int? ReadingNumber { get; set; }
    public string RealPostId { get; set; }
    public string Url { get; set; }
    public string Category { get; set; }
    public DateTime PublishedTime { get; set; }    
}

我想在 PostController 中编写一个返回我 RealBlogId 的函数使用 postId

 public class PostController : Controller
  {
     private ReaderDb db = new ReaderDb();

     public ActionResult Details(int? postId)
     {
        if (postId == null)
        {
            return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
        }
        Post post = db.Posts.Find(postId);
        if (post == null)
        {
            return HttpNotFound();
        }
            IQueryable<string>realPostId = from r in db.Posts 
            where r.Id == id   //This query gives me realPostId
            select r.RealId;

          //second query

 }

我如何编写一个在第二个查询中返回 realBlogId 的查询

Answer 1

这是一种方法:

var query = from post in db.Posts
            from blog in db.Blogs
            where post.BlogId == blog.Id && post.Id == postId
            select blog.RealBlogId;

var result = query.FirstOrDefault();

更好的方法是修改模型，使它们之间的关系明确如下:

public class Blog
{
    public Blog()
    {
        Posts = new HashSet<Post>();
    }

    public int Id { get; set; }
    public virtual ICollection<Post> Posts { get; set; }

    //Rest of properties here
}

public class Post
{
    public int Id { get; set; }

    public int? BlogId { get; set; }
    public virtual Blog Blog { get; set; }
    //Reset of properties here

}

这将允许您创建这样的查询:

var result = db.Posts
    .Where(x => x.Id == postId)
    .Select(x => x.Blog.RealBlogId) //Notice how we reference Post.Blog here
    .FirstOrDefault();