实体框架linq查询包含（）多个子实体 [英] Entity framework linq query Include() multiple children entities

问题描述

这可能是一个非常重要的问题，但是当编写跨越三级（或更多）的查询时，包含多个子实体的好方法是什么？

This may be a really elementry question but whats a nice way to include multiple children entities when writing a query that spans THREE levels (or more)?

我有4个表：公司，员工， Employee_Car 和 Employee_Country

公司与Employee有1：m的关系。

Company has a 1:m relationship with Employee.

Employee与Employee_Car和Employee_Country都有1：m的关系。

Employee has a 1:m relationship with both Employee_Car and Employee_Country.

如果我想写一个从所有4个表返回数据的查询，我我正在写：

If i want to write a query that returns the data from all 4 the tables, I am currently writing:

Company company = context.Companies
                         .Include("Employee.Employee_Car")
                         .Include("Employee.Employee_Country")
                         .FirstOrDefault(c => c.Id == companyID);

必须有一个更优雅的方式！这是长时间的，并产生可怕的SQL

There has to be a more elegant way! This is long winded and generates horrendous SQL

我在VS 2010中使用EF4

I am using EF4 with VS 2010

推荐答案

使用扩展方法。
将 NameOfContext 替换为对象上下文的名称。

Use extension methods. Replace NameOfContext with the name of your object context.

public static class Extensions{
   public static IQueryable<Company> CompleteCompanies(this NameOfContext context){
         return context.Companies
             .Include("Employee.Employee_Car")
             .Include("Employee.Employee_Country") ;
     }

     public static Company CompanyById(this NameOfContext context, int companyID){
         return context.Companies
             .Include("Employee.Employee_Car")
             .Include("Employee.Employee_Country")
             .FirstOrDefault(c => c.Id == companyID) ;
      }

}

然后你的代码变成

     Company company = 
          context.CompleteCompanies().FirstOrDefault(c => c.Id == companyID);

     //or if you want even more
     Company company = 
          context.CompanyById(companyID);

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