为什么在简单的一对多关系上使用 LINQ Join? [英] Why use LINQ Join on a simple one-many relationship?

问题描述

我已经使用 LINQ to SQL 和实体框架几年了，而且我总是映射我的数据库关系以生成相关的导航属性.而且我总是使用导航属性.

I've been using LINQ to SQL and Entity Framework for a few years and I've always mapped my database relationships to generate the relevant navigation properties. And I always use the navigation properties.

我错过了什么吗?

如果我有一个 Category->Products 一对多类型的关系，我会使用

If I have a Category->Products one-many type relationship, I would use

var redProducts = context.Category.Single(c => c.Name = "red").Products;

我经常看到人们在整个网站、在线项目和各种其他网站中进行手动连接.

I regularly see people doing manual joins, all over this site, in projects online, and various other websites.

var employer = from category in context.Categories
               join product in context.Products
               on category.CategoryId equals product.CategoryId
               where category.Name == "red"
               select product;

那么 - 为什么?使用这种 Join 语法有什么好处?

So - why? What are the benefits of using this Join syntax?

推荐答案

这通常是一个错误.

@George 是正确的，您的两个示例在功能上有所不同，但与 join 与非 join 无关.但是你可以很容易地写:

@George is correct that your two examples are functionally different in a way which has nothing to do with join vs non-join, however. But you could just as easily write:

var redProducts = context.Category
                         .Where(c => c.Name == "red")
                         .SelectMany(c => c.Products);

...在功能上与您的 join 示例完全相同(但从可读性和可维护性 POV 来看，优于).

...which is functionally identical (but superior from a readability and maintainability POV) to your join example.

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