扩展方法的用法-这不是一个糟糕的设计吗？-Extensionmethodsusage-Isn'tthisbaddesign?

5  

The point is that if you've implemented all of IRepository appropriately, you (as the data layer implementor) don't have to know about root categories at all. For the scope of this extension method, it is assumed that any repository of categories will have a root category of ID 1. That may well be a perfectly reasonable assumption, and a useful one: no-one has to build a derived class (which may well be impractical - the data layer may have factories etc which make it tricky to derive from the implementations).

关键是如果你已经适当地实现了所有的IRepository ,你(作为数据层实现者)根本不必知道根类别。对于此扩展方法的范围,假设任何类别的存储库都将具有ID 1的根类别。这可能是一个非常合理的假设,并且是一个有用的假设:没有人必须构建派生类(其中可能是不切实际的 - 数据层可能有工厂等,这使得从实现派生出来很棘手)。

Now, the extension method is only applicable if its scope is appropriate - if it's in a namespace (or closely related one) where that assumption about root categories will be valid.

现在,扩展方法仅适用于其范围适当的情况 - 如果它位于命名空间(或密切相关的范围)中,其中关于根类别的假设将是有效的。

I don't think the "older" way would really be an interface extending IRepository - it would be a normal static method taking IRepository. That's where extension methods just make life more pleasant. If you really would have used inheritance instead, it may well be appropriate to do so now as well. Unfortunately we don't know enough about the architecture of your system to say that for sure.

我不认为“较旧”的方式实际上是扩展IRepository 的接口 - 它将是一个采用IRepository 的常规静态方法。这就是扩展方法让生活更愉快的地方。如果你真的会使用继承,那么现在也可以这样做。遗憾的是,我们对您系统的架构知之甚少。

4  

Extension methods concept is just syntactic sugar as some authors call it. It makes the code more readable though less understandable. Ultimately extension methods are just static ones which are the heritage of the procedural paradigm. They make the code tightly-coupled and less cohesive, harder to test and reuse.

扩展方法概念只是一些作者所称的语法糖。它使代码更具可读性,但不太容易理解。最终,扩展方法只是静态方法,是程序范式的遗产。它们使代码紧密耦合,内聚力更低,更难以测试和重用。

I am biased against this tendency of the C# programming language. This feature is attractive but it doesn't bring any benefits, quite the contrary it increases the complexity of the code.

我对C#编程语言的这种倾向有偏见。此功能很有吸引力,但它没有带来任何好处,恰恰相反,它增加了代码的复杂性。

1  

It's not the same thing. An extension method is a syntactic convenience, nothing more, and certainly not a contractual requirement. You don't "implement" them on your own classes. For your example above:

这不是一回事。扩展方法是一种语法上的便利,仅此而且当然不是合同要求。你不要在自己的课上“实施”它们。对于上面的例子:

using CategoryRepositoryExtensions;
...
Category c = r.GetRootCategory();

is exactly the same as:

与以下内容完全相同:

Category c = CategoryRepositoryExtensions.GetRootCategory(r);

and therefore there is no additional requirement on the implementer of the interface.

因此对接口的实现者没有额外的要求。

0  

Yes in the example you mentioned it does seem counter-intuitive and the reason is because you are working with a single object at a single level. I find that extension methods are most useful when you are working with IQueryable / IEnumerable collections.

是的,在您提到的示例中,它看起来似乎是违反直觉的,原因是因为您在单个级别上处理单个对象。当您使用IQueryable / IEnumerable集合时,我发现扩展方法最有用。

For eg. lets consider 2 scenarios:

例如。让我们考虑两种情况:

• Scenario 1: get list of all orders which contain product x

  场景1:获取包含产品x的所有订单的列表

• Scenario 2: get list of all orders which contain product x and have been shipped to zipcode y

  场景2:获取包含产品x并已发送到zipcode y的所有订单的列表

If you were using the traditional/interface driven approach you might define 2 be tempted to define 2 different interfaces. If you use extension methods, you could use something like the following

如果您使用传统/接口驱动的方法,您可能会定义2被诱惑定义2个不同的接口。如果使用扩展方法,则可以使用以下内容

Scenario 1

 orders1Enumerable = OrderRepository.GetAllOrders()
                                     .ContainingProductCode(x);

Scenario 2

 orders2Enumerable = OrderRepository.GetAllOrders()
                                     .ContainingProductCode(x)
                                     .WithShippingZipCode(y);

When you do this, the framework creates the appropriate SQL on the fly by chaining these extension methods

执行此操作时,框架会通过链接这些扩展方法来动态创建适当的SQL

Hope this helps

希望这可以帮助