LINQ2SQL，存储库模式 - 如何从两个或多个表中查询数据？ [英] linq2sql, repository pattern - how to query data from two or more tables?

问题描述

我使用Repository模式（和LINQ2SQL作为数据存取），并具有例如，ProductsRep和CustomersRep。

I use Repository pattern (and linq2sql as data access) and have, for example, ProductsRep and CustomersRep.

在很简单的场景数据库有两个表 - Produsts 的（产品ID，客户ID，产品名称，日期）和客户的（客户ID，名字，姓氏）。

In very simple scenario db has two tables - Produsts (ProductID, CustomerID, ProductName, Date) and Customer (CustomerID, FirstName, LastName).

每个库提供的方法来创建，更新，删除和获取具体型号的对象，可能是，一些过滤器。

Each repository provide methods to create, update, delete and get specific model object, and, may be, some filters.

但是，如果我想查询由产品名购买特定产品的所有客户，我得使用ProductsRep本产品的产品ID，然后得到购买产品的使用CustomersRep此ID的所有客户。

But if I want to query all customers that buy specific product by product name, I have to get ProductID of this product using ProductsRep and then get all customers that buy product with this id using CustomersRep.

我说得对不对？这是L2S必须产生实际上是两个SQL请求，是有可能这样做只有一个要求吗？

Am I right? This is actually two sql requests that l2s must generate, is it possible to do only one request?

和，一般来说，如果我们要使用多个表与关系和存储库的模式来查询数据时，如何做到这一点通过查询量减少到最低限度？

And, in general, if we want to query data using multiple tables with relationships and repository pattern, how to do this by reduce amount of queries to minimum?

感谢。

推荐答案

想想你的发言：

但是，如果我想查询所有客户
  根据产品购买特定产品
  名字，我得这个产品ID
  使用产品ProductsRep然后得到
  那买的产品与所有客户
  这个ID使用CustomersRep。

But if I want to query all customers that buy specific product by product name, I have to get ProductID of this product using ProductsRep and then get all customers that buy product with this id using CustomersRep.

这闻起来麻烦。 创建信息库，以方便行为域的隔离区，而不是针对每个业务实体。

与DDD /存储库一个常见的​​错误是认为有关数据。别。想想行为。

A common mistake with DDD/Repository is to think about data. DONT. Think about behaviour.

您拥有的产品实体，指的客户即可。这意味着产品离不开客户的存在。对？因此，一个客户是聚合根 - 它控制你的域模型的这一部分的行为

You have a Products entity which refers to a Customer. Which means a Product cannot exist without a customer. Right? Therefore a Customer is your aggregate root - it controls the behaviour of this portion of your domain model.

您上面的回答评论确认 - 要跨多个存储库工作。你有两个选择 - 1）的工作单位，2）修复了你的资料库的设计

Your comment to the answer above confirms that - you are working across multiple repositories. You have two options - 1) unit of work, 2) fix up your repository design.

您只需要1库 - 我们称之为 CustomerProductRepository

You only need 1 Repository - let's call it CustomerProductRepository.

然后做你上面的查询：

var customersWhoBuyHats = customerProductRepository
                             .Products
                             .Include("Customer")
                             .Where(x => x.ProductName == "Hat")
                             .Select(x => x.Customer)
                             .ToList();

结果是一个 列表＆LT;客户方式＆gt; ，然后你与一个数据库调用做到了

The result is a List<Customer>, and you did it with one database call.

心连心。

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