Linq with Left Join on SubQuery包含Count

没有经过测试,但这应该可以解决问题:

var q = from c in ctx.Category
        join clg in 
            (
                from cl in ctx.CategoryListing
                group cl by cl.CategoryID into g
                select new { CategoryID = g.Key, Frequency = g.Count()}
            ) on c.CategoryID equals clg.CategoryID into cclg
        from v in cclg.DefaultIfEmpty()
        where c.GuideID==1
        select new { c.CategoryID, Frequency = v.Frequency ?? 0 };