如何使用LINQ to SQL处理IN子查询？

var subquery = from item in db.Items
                where item.Category == "Category1"
                select item.Id;

var query = from item in db.Items
            where subquery.Contains(item.Id)
            select item;

var query = from item in db.Items
            where db.Items.Any(subitem => subitem.Category == "Category1" && subitem.Id == item.Id)
            select item;

var subquery = from item in db.Items
                where item.Category == "Category1"
                select item.Id;

var query = from item in db.Items
            join subitem in subquery on item.Id equals subitem
            select item;