Question

How would you convert this SQL statement to LINQ, most efficient ?

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

This is the LINQ query I’ve got right now:

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

This should produce the exact same query (excluding the seemingly unnecessary use of the Items table) and is much more natural to me IMHO.

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(),
            };

If the join makes you queasy for whatever reason, here’s an alternative.

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