如何在多處理很多關係

Question

我想實現這樣的空值： 如果有那麼一個匹配的ID根據它過濾後的結果，否則繞過條件

.Where(x => x.NeighbourhoodId == (id ?? x.NeighbourhoodId) 

，但我不得到了許多正確的語法一對多的關係：

public JsonResult GetPost(int? id, int? tagid) 
    { 
    var ret = from data in db.Posts.Include(x => x.Tags) 
       .Include(x => x.Neighbourhood) 
       .OrderByDescending(x => x.PostedDate) 
       .Where(x => x.NeighbourhoodId == (id ?? x.NeighbourhoodId) 
       && x.Tags.Any(t => t.TagId == tagid)) 
       .ToList() 
       select new 
        { 
         TagName = string.Join(",", data.Tags.Select(t => t.TagName)), 
         Message = data.Message, 
        // and other related stuff 
        } 

這裏，就像你看到的，這個where子句中包含多個條件，我想篩選post.There將是唯一一個值參數。意味着如果id參數有值，那麼tagid將爲null，如果tagid爲null，那麼id會有一些值。

現在，我想如果tagid中有空值，那麼這個查詢仍然應該運行。現在，它沒有在數據庫中工作becoz，沒有空的tagid或null的帖子，如何做到這一點。有什麼建議麼？？

Answer 1

如果我理解正確的話，你需要建立動態的基礎上傳遞的參數是這樣

var posts = db.Posts 
    .Include(x => x.Tags) 
    .Include(x => x.Neighbourhood) 
    .OrderByDescending(x => x.PostedDate); 
if (id != null) 
    posts = posts.Where(x => x.NeighbourhoodId == id.Value); 
if (tagid != null) 
    posts = posts.Where(x => x.Tags.Any(t => t.TagId == tagid.Value)); 
var ret = from data in posts 
    // ... the rest