LINQ查询的论坛

Question

我编码这个论坛，因为我是新来的LINQ我就遇到了这个问题，当用户点击主页。我想显示的论坛列表像这样的表：

Forum  --- Topics (count) --- Posts (count) --- LastPostUserId --- LastPostTime

我有以下SQL表：

Forums:
ForumId (int32),
Title (string),
Description (string)

ForumThreads:
ThreadId (int32),
ForumId (int32),
UserId (guid),
Subject (string),
Views (int32),
CreateDate (DateTime)

ForumPosts:
PostId (int32),
ThreadId (int32),
UserId (guid),
Post (string),
CreateDate (datetime)

感谢您......

Answer 1

有关，如果你使用的会员，你不希望在您的dbml的aspnet_Users显示用户名：

...
LastPostUserId = posts.OrderByDescending(p=>p.PostId).Take(1).Select(p=> Membership.GetUser(p.UserId))
...

另外一个变化，让您的样品贴好一点是添加orderbydescending变量的帖子： 然后可以从select子句丢弃4次重复OrderByDescending：

from forum in Forums
let posts = ForumPosts.Where(p => p.ForumThreads.ForumId.Equals(forum.ForumId)).OrderByDescending(p=>p.PostId)
select new
{
    Forum = forum.Title,
    Description = forum.Description,
    Topics = forum.ForumThreads.Count(),
    Posts = posts.Count(),
    LastPostId = posts.Take(1).Select(p=>p.PostId),
    LastPostThreadId = posts.Take(1).Select(p=>p.ThreadId),
    LastPostUserId = posts.Take(1).Select(p=>p.UserId),
    LastPostTime = posts.Take(1).Select(p=>p.CreateDate)
}

或者甚至清洁器：

from forum in Forums
let posts = ForumPosts.Where(p => p.ForumThreads.ForumId.Equals(forum.ForumId))
let lastPost = posts.OrderByDescending(p=>p.PostId).Take(1)
select new
{
    Forum = forum.Title,
    Description = forum.Description,
    Topics = forum.ForumThreads.Count(),
    Posts = posts.Count(),
    LastPostId = lastPost.PostId,
    LastPostThreadId = lastPost.ThreadId,
    LastPostUserId = lastPost.UserId,
    LastPostUserName = Membership.GetUser(lastPost.UserId),
    LastPostTime = lastPost.CreateDate
}

测试此代码时，有没有最新帖子寿，我认为这可能会引发一个错误，如果采取（1）为空..

Answer 2

from forum in forums
from posts in db.ForumPosts.Where(p => p.Thread.ForumId.Equals(forum.ForumId))
select new
{
Forum = forum.Title, 
Topics = forum.ForumThreads.Count(),
Posts = posts.Count(),
LastPostBy = posts.OrderByDescending(p => p.CreateDate).FirstOrDefault(p => p.UserId),
LastPostTime= posts.Max(p => p.CreateDate))
}

未经测试ofcourse，但试图从这里开始并检查SQL查询（S）后执行，让我知道，如果它需要优化。

Answer 3

这几乎是卓有成效的（尽管它产生一些可怕的SQL; - ）...）

from forum in Forums
let posts = ForumPosts.Where(p => p.ForumThreads.ForumId.Equals(forum.ForumId))
select new
{
    Forum = forum.Title,
    Description = forum.Description,
    Topics = forum.ForumThreads.Count(),
    Posts = posts.Count(),
    LastPostId = posts.OrderByDescending(p=>p.PostId).Take(1).Select(p=>p.PostId),
    LastPostThreadId = posts.OrderByDescending(p=>p.PostId).Take(1).Select(p=>p.ThreadId),
    LastPostUserId = posts.OrderByDescending(p=>p.PostId).Take(1).Select(p=>p.UserId),
    LastPostTime = posts.OrderByDescending(p=>p.PostId).Take(1).Select(p=>p.CreateDate)
}

最后一件事 - 我有一个从SQL表“ForumPosts”的关系为“Aspnet_Users”，我想显示的列Aspnet_Users.UserName作为LastPostUserName ......这怎么办呢？而且你会如何优化整个查询？