如何在C#实体框架Linq中编写左联接，分组和平均

本文介绍了如何在C#实体框架Linq中编写左联接，分组和平均的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

简单来说，我需要在实体框架中编写以下SQL.我宁愿在Lynq中这样做.我正在使用mysql

To put it in simple terms i need to write the following SQL in entity framework. I would prefer to do it in Lynq. I'm using mysql

SELECT `p`.`Id`, p.price, p.categoryid, avg(o.rate) FROM `Product` AS `p` LEFT JOIN `Order` AS `o` ON `p`.`Id` = `o`.`ProductId` group by p.id

我到目前为止所做的是下面的

What I have did so far is below

var data = from p in _context.Product join o in _context.Order on p.Id equals o.ProductId into orderTemp from ord in orderTemp.DefaultIfEmpty() group p by p.Id into gp select new { p.Id, p.Price, p.CategoryId, gp.Average(m => m.Rate) };

我整天都在努力做这件事.任何帮助将是非常有价值的，并受到赞赏.预先谢谢你.

I have been struggling o do this the whole day. Any help would be highly valuable and appreciated. Thank you in advance.

以上操作无效，因为 m 引用了 Product 的对象.

The above is not working, as m is referencing the object of Product.

推荐答案

感谢所有尝试帮助我的人.经过一番努力，下面的东西对我有用.

Thank you everyone who tried to help me out. After a struggle the below worked for me.

var data = from p in _context.Product join o in _context.Order on p.Id equals o.ProductId into orderTemp from ord in orderTemp.DefaultIfEmpty() group ord by p into gp select new { Id = gp.Key.Id, Price = gp.Key.Price, CategoryId = gp.Key.CategoryId, Rate = gp.Average(m => m == null ? 0 : m.Rate) };