Question

当我尝试将此SQL循环到LINQ方法时，我只接收了forum_category的所有行。我真正希望它做的是从forum_category获取所有行，并返回所有与类别ID匹配的论坛，这是预期的结果：

FORUM_CATEGORY (categoryid, categorytitle)
 - FORUM (forumid, forumtitle, forumdescrition) -> (latest topic => topicid, topictitle) -> (latest post on that latest topic => postid, postadded, username) -> total topic count, total post count in this forum only
 - FORUM (forumid, forumtitle, forumdescrition) -> (latest topic => topicid, topictitle) -> (latest post on that latest topic => postid, postadded, username) -> total topic count, total post count in this forum only
 - FORUM (forumid, forumtitle, forumdescrition) -> (latest topic => topicid, topictitle) -> (latest post on that latest topic => postid, postadded, username) -> total topic count, total post count in this forum only

FORUM_CATEGORY
 - FORUM [...]
 - FORUM [...]
 - FORUM [...]

你明白了......

-

这是我目前得到的：

FORUM_CATEGORY
 - FORUM (forumid, forumtitle, forumdescrition) -> (latest topic => topicid, topictitle) -> (latest post on that latest topic => postid, postadded, username) -> total topic count, total post count in this forum only

FORUM_CATEGORY
 - FORUM (forumid, forumtitle, forumdescrition) -> (latest topic => topicid, topictitle) -> (latest post on that latest topic => postid, postadded, username) -> total topic count, total post count in this forum only

也就是说，每个论坛类别只有一个论坛。这是LINQ代码：

var forum = (from c in context.forum_category
             join f in context.forum on c.id equals f.categoryid
             join t in context.forum_topic on f.id equals t.forumid
             join tc in context.forum_topic on f.id equals tc.forumid into tcount
             join p in context.forum_posts on t.id equals p.topicid
             join pc in context.forum_posts on t.id equals pc.topicid into pcount
             join u in context.users on p.userid equals u.id
             orderby p.added descending
             select new ForumIndexModel
                        {
                            CategoryId = c.id,
                            CategoryTitle = c.title,

                            ForumId = f.id,
                            ForumTitle = f.title,
                            ForumDescription = f.description,
                            TopicId = t.id,
                            TopicTitle = t.title,

                            PostId = p.id,
                            PostAdded = p.added,

                            Username = u.username,

                            TopicCount = tcount.Count(),
                            PostCount = pcount.Count()
                        }).ToList();
return View(forum);

这只是我所做的一些不同方法的一个例子。

编辑：澄清我想要的更具体的内容。

Answer 1

我将根据原始海报的要求添加另一个答案。我正在使用实体框架，并且在我的示例中使用了已定义的关联。我的数据模型（出于本示例的目的）是三个表，因为存在多对多的关系，但是只有一对多关系的类别和论坛表（加上addtl。查找表）会更简单。

所以我的数据模型（物理）

lm_m_category
lm_m_category_link（这是多对多表）
lm_m_link

我在EF中定义了关联（ nCat ， nLink 用于导航到类别或从外部参照表链接）。 EF以这种方式处理连接。

所以加载它的代码不是一个声明，但是你让我告诉你如何使用EF来实现它。我没有把Category和Link类的例子放在简单的id，desc类但是Category有一个Links列表。我的物理数据模型使用lm_m_ *表。

List<Category> Categories = new List<Category>();

Category newCategory;
Link newLink;

foreach (var category in db.lm_m_category_link.Include("nCategory").Include("nLink").ToList())
    {
    newCategory = new Category();

    newCategory.category_id = category.category_id;
    newCategory.category_name = category.nCategory.nCat.category_name;

    foreach (var link in (IEnumerable<lm_m_link>)category.nLink)
    {
        newLink = new Link();

        newLink.link_id = link.link_id;
        newLink.link_name = link.link_title;
        newLink.link_url = link.link_url;

        // add link to list
        newCategory.category_links.Add(newLink);
    }

    // add category 
    Categories.Add(newCategory);
}

Answer 2

我虽然你的排序引起了问题，但经过进一步的审查......

我还有另外一个想法，你的 ForumIndexClass看错了，你想要什么。您的ForumIndexModel不应该在论坛列上有列表（或IEnumerable）吗？您正在分配应该有列表的单个值。你的课看起来应该更像......

class ForumIndexModel { int CategoryId {get; set;} string CategoryTitle {get; set;} List<int> ForumIds {get; set;} List<string> ForumTitles {get; set;} List<string> ForumDescriptions {get; set;} ... you get the idea... }

要选择列表，请执行以下操作：

public class C { A TheA {get;set;} List<B> TheBs {get;set;} } //g is an IEnumerable<B> with a key property of A List theResult = ( from a in ListA join b in ListB on a.ValueAB = b.ValueAB into g select new C() { TheA = g.Key, TheBs = g.ToList() } ).ToList();

如何遍历几个左连接LINQ to SQL

2 个答案: