此SQL到LINQ

Question

如何將此SQL語句轉換爲LINQ，效率最高？

SELECT categoryName, 
     (SELECT COUNT(*) cnt 
     FROM itemCategories 
     WHERE (categories.categoryId = itemCategories.categoryId) 
      AND (Items.countryPartId = 1)) AS cnt 
    FROM categories, Items 

這是LINQ查詢我有現在：

var q = 
    from c in context.categories 
    select new CategoryCount 
    { 
     CategoryName = c.categoryName, 
     Counter = (
      from i in context.itemCategories 
      where c.categoryId == i.categoryId 
      select i).Count() 
    }; 

Answer 1

這應該產生完全相同的查詢（不包括看似不必要的使用Items表），是恕我直言，更自然的我。

var query = from c in context.categories 
      join ic in context.itemCategories 
       on c.categoryId equals ic.categoryId into joined 
      select new CategoryCount 
      { 
       CategoryName = c.categoryName, 
       Counter = joined.Count(), 
      }; 

如果加入讓你因任何原因而陷入que，，這裏有一個選擇。

var query = from c in context.categories 
      select new CategoryCount 
      { 
       CategoryName = c.categoryName, 
       Counter = context.itemCategories 
           .Where(ic => ic.categoryId == c.categoryId) 
           .Count(), 
      }; 

Answer 2

我想我自己。很抱歉造成您的不便史蒂芬，就不會再發生了:)

var q = (from c in context.categories 
     from it in context.Items 
     select new CategoryCount 
     { 
      CategoryName = c.categoryName, 
      Counter = (from i in context.itemCategories 
        where c.categoryId == i.categoryId && it.countryPartId == 1 select i).Count() 
     });