如何将 SQL 中的多个内部联接转换为 LINQ?

问题描述

我已经掌握了 LINQ-to-SQL 的基础知识，但我一直在努力让 JOIN 正常工作.我想知道如何将以下内容转换为 LINQ-to-SQL(最好使用方法链，因为这是我的首选格式).

I've got the basics of LINQ-to-SQL down, but I've been struggling trying to get JOINs to work properly. I'd like to know how to convert the following to LINQ-to-SQL (ideally using method chaining, as that is my preferred format).

SELECT      c.CompanyId, c.CompanyName,
            p.FirstName + ' ' + p.LastName as AccountCoordinator,
            p2.FirstName + ' ' + p2.LastName as AccountManager
FROM        dbo.Companies c
INNER JOIN  dbo.Persons p
ON          c.AccountCoordinatorPersonId = p.PersonId
INNER JOIN  dbo.Persons p2
ON          c.AccountManagerPersonId = p2.PersonId

推荐答案

使用查询语法:

from c in dbo.Companies
join p in dbo.Persons on c.AccountCoordinatorPersonId equals p.PersonId
join p2 in dbo.Persons on c.AccountManagerPersonId equals p2.PersonId
select new
{
    c.CompanyId,
    c.CompanyName,
    AccountCoordinator = p.FirstName + ' ' + p.Surname,
    AccountManager = p2.FirstName + ' ' + p2.Surname
}

使用方法链:

dbo.Companies.Join(dbo.Persons, 
                   c => c.AccountCoordinatorPersonId,  
                   p => p.PersonId,  
                   (c, p) => new 
                   {  
                       Company = c,  
                       AccountCoordinator = p.FirstName + ' ' + p.Surname  
                   })
             .Join(dbo.Persons,  
                   c => c.Company.AccountManagerPersonId,  
                   p2 => p2.PersonId,  
                   (c, p2) => new 
                   {  
                       c.Company.CompanyId,  
                       c.Company.CompanyName,  
                       c.AccountCoordinator,  
                       AccountManager = p2.FirstName + ' ' + p2.Surname 
                   });