优化 Linq 查询：order by

Question

我有以下 Linq 查询，我发现我在其中执行 join 和 order by 的 LastRenewed 调用需要将近一分钟。以 out 的顺序将查询时间减少 30 秒。有没有办法优化 LastRenewed 调用？

from stats in db.Stats 
group stats by stats.Id into st
join logs in db.Logs on st.Key equals logs.Id
select new
{
    //bunch of queries
    ... 
    LastRenewed = (from books in (db.Books.Where(x => x.BookId == st.Key))
                   join customer in db.Customers on books.Id equals customer.Id
                   orderby customer.LastRenewed descending
                   select customer.LastRenewed)
                  .FirstOrDefault(),
    ...
}

Answer 1

获取db.Books.Where(x => x.BookId == st.Key) 并将其存储在查询之外，然后像这样使用它：

object books = `db.Books.Where(x => x.BookId == st.Key)`
LastRenewed = (from books in (books))
               join customer in db.Customers on books.Id equals customer.Id
               orderby customer.LastRenewed descending
               select customer.LastRenewed)
              .FirstOrDefault(),

这应该会有所帮助。