为什么要在ASP.NET MVC中使用数据库工厂? [英] Why use database factory in asp.net mvc?

问题描述

最近我已经使用过asp.net mvc，并且在示例项目中看到的是使用Database Factory类.您如何为我解释为什么使用它?

Recently I have worked with asp.net mvc and I have seen in sample project is using Database Factory class. How can you explain for me why use it ?

IDatabaseFactory类

IDatabaseFactory class

public interface IDatabaseFactory : IDisposable
{
    EFMVCDataContex Get();
}

DatabaseFactory类

DatabaseFactory class

public class DatabaseFactory : Disposable, IDatabaseFactory
{
    private EFMVCDataContex dataContext;
    public EFMVCDataContex Get()
    {
        return dataContext ?? (dataContext = new EFMVCDataContex());
    }
    protected override void DisposeCore()
    {
        if (dataContext != null)
            dataContext.Dispose();
    }
}

推荐答案

这是抽象工厂的示例设计模式.想法是创建一个接缝，以在类之间提供松散的耦合，以便可以出于测试目的或扩展应用程序而交换另一种类型的上下文.

This is an example of an Abstract Factory design pattern. The idea is to create a seam to provide loose coupling between the classes so another type of context could be swapped, either for testing purposes or to extend the application.

一般而言，工厂是一种管理短期依赖项(例如数据库连接)的方法.通常，框架公开一种注入工厂实例的方法，然后该框架可以基于接口(在本例中为IDatabaseFactory)作为框架与框架用户之间的契约来使用它.该框架将具有类似于以下内容的代码:

Generally speaking, a factory is a way to manage short-lived dependencies, such as database connections. Typically, a framework exposes a way to inject an instance of the factory and then the framework can work with it based on an interface (in this case IDatabaseFactory) as a contract between the framework, and the framework user. The framework will have code that looks something like this:

public interface ISomeService
{
    void DoSomething();
}

public class SomeService()
{
    private readonly IDatabaseFactory factory;

    // The factory is injected through the constructor
    public SomeService(IDatabaseFactory factory)
    {
        this.factory = factory;
    }

    public void DoSomething()
    {
        using (EFMVCDataContex context = this.factory.Get())
        {
            // Run a LINQ query here using the context

        } // This bracket disposes the context
    }
}

与服务端创建的上下文相比，服务实例化的寿命更长.更重要的是，在这种情况下，上下文始终可以正确处理.

The service can then be instantiated for a much longer lifetime than the context that is created by the factory. What's more is that the context is always properly disposed in this scenario.

现在，这样做的主要好处是您可以将DatabaseFactory与替代实现互换(通常称为

Now, the main benefit from doing this is that you can swap the DatabaseFactory with an alternate implementation (commonly referred to as the Liskov Substitution Principle):

public class MyDatabaseFactory : Disposable, IDatabaseFactory
{
    private EFMVCDataContex dataContext;
    public EFMVCDataContex Get()
    {
        return dataContext ?? (dataContext = new AlternateDataContext());
    }

    protected override void DisposeCore()
    {
        if (dataContext != null)
            dataContext.Dispose();
    }
}

假设AlternateDataContext继承(或实现)EFMVCDataContex，可以将MyDatabaseFactory与DatabaseFactory进行苹果换苹果，而无需对SomeService进行任何更改.

Assuming that AlternateDataContext inherits (or implements) EFMVCDataContex, MyDatabaseFactory can be swapped apples-for-apples with DatabaseFactory without making any changes to SomeService.

MyDatabaseFactory可以在构造函数中使用连接字符串进行编码，例如，为您提供了一种连接备用数据库的方法.

MyDatabaseFactory could be coded with a connection string in the constructor, giving you a way to connect to alternate databases, for example.

当然，这样做的另一个好处是创建了IDatabaseFactory的模拟实现，该实现可用于测试DoSomething方法.在单元测试中，SomeService(被测类)应该是唯一使用的真实类，IDatabaseFactory应该是模拟类(可以通过手动编码一个类或使用模拟框架来完成).

Of course, another great benefit of doing this is to create a mock implementation of IDatabaseFactory that can be used to test the DoSomething method. In a unit test, SomeService (the class under test) should be the only real class being used, IDatabaseFactory should be a mock (which could either be done by hand coding a class, or using a mocking framework).

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