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

问题描述

这可能是一个非常基本的问题，但在编写跨越三个级别(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)?

即我有 4 个表:Company、Employee、Employee_Car 和 Employee_Country

i.e. I have 4 tables: Company, Employee, Employee_Car and Employee_Country

公司与员工是一对一的关系.

Company has a 1:m relationship with Employee.

Employee 与 Employee_Car 和 Employee_Country 有 1:m 的关系.

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

如果我想编写一个返回所有 4 个表中数据的查询，我目前正在编写:

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);

必须有更优雅的方式！这是冗长的并生成可怕的 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 extension方法.将 NameOfContext 替换为您的对象上下文的名称.

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) ;
      }

}

那么你的代码就变成了

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

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

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