数据访问层（DAL）中的LINQ查询方法

发布于 2024-10-01 01:44:16 字数 688 浏览 1 评论 0原文

一个基于经典三层的项目：UI（在这个问题中并不重要）、业务逻辑层和数据访问层。我有几个表：客户 产品 订单 用户。设计应该是：

//DAL methods
public IEnumerable<Customer> GetAllCustomers()
public IEnumerable<Product> GetAllProducts()
public IEnumerable<Order> GetAllOrders()
public IEnumerable<User> GetAllUsers()
//BLL methods
public IEnumerable<Order> GetOrders(long CustomerID)
public IEnumerable<Product> GetProducts(long CustomerID)
public IEnumerable<Product> GetProducts(long OrderID)

让我困惑的是，我发现DAL中的所有方法都是GetAllXXXX。我不得不承认这个设计效果很好。在 DAL 中，只有 GetAll 方法。在 BLL 中，除了 GetAll 方法的组合操作（过滤/连接/选择）之外什么也没有。很奇怪吗？正确的方法是什么？

原文

A project base on classic 3 layers: UI(not important in this question), business logic layer and data access layer. I have several tables: Customers Products Orders Users. The design is supposed to be:

//DAL methods
public IEnumerable<Customer> GetAllCustomers()
public IEnumerable<Product> GetAllProducts()
public IEnumerable<Order> GetAllOrders()
public IEnumerable<User> GetAllUsers()
//BLL methods
public IEnumerable<Order> GetOrders(long CustomerID)
public IEnumerable<Product> GetProducts(long CustomerID)
public IEnumerable<Product> GetProducts(long OrderID)

What confuses me is that I find that all methods in DAL are GetAllXXXX. And I have to admit that this design is working fine. In DAL there is nothing but GetAll methods. In BLL there is nothing but combined operations(filter/join/select) to GetAll methods. Is it weird? What's the correct way?

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拥抱我好吗 2024-10-08 01:44:17

不，这并不奇怪，事实上这与我的做法非常相似。

对我来说唯一的区别是：

我使用 IQueryable 而不是 IEnumerable （为了获得延迟执行）
我有一个通用存储库（Repository））：IQueryable;查找() 无效添加(T) 等等等等

这样，我的存储库保持干净/简单。

因此，您的 BLL 可以这样实现：

public IEnumerable<Order> GetOrders(long CustomerID)
{
   Repository<Order> orderRepository = new Repository<Order>(); // should use DI here, but i digress
   return orderRepository
             .Find() // no query executed...
             .Where(o => o.CustomerID == CustomerID) // still nothing...
             .ToList(); // query executed, with BL applied! cool!
}

使 BLL 执行投影/工作/逻辑。存储库只处理 T 的持久性，不关心实际类型或任何业务逻辑。

无论如何，我就是这样做的。

No, that's not weird, and in fact that is very similar to how i do it.

Only differences for me:

I use IQueryable<T> instead of IEnumerable<T> (to get deferred exec)
I have a generic repository (Repository<T>):
- IQueryable<T> Find()
- void Add(T)
- etc etc

This way, my repositories stay clean/simple.

So your BLL could be implemented like this:

public IEnumerable<Order> GetOrders(long CustomerID)
{
   Repository<Order> orderRepository = new Repository<Order>(); // should use DI here, but i digress
   return orderRepository
             .Find() // no query executed...
             .Where(o => o.CustomerID == CustomerID) // still nothing...
             .ToList(); // query executed, with BL applied! cool!
}

Makes the BLL do the projection/work/logic. Repositories just handle persistence of T, doesn't care about the actual type, or any business logic.

That's how i do it anyway.

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