方法链等价?

我将重新排序查询以筛选出 companyName

var query = db.Companies.Where(c => c.CompanyName == companyName)
              .Join(db.Persons, c => c.CompanyId, p => p.CompanyId, (p, c) => p)
              .Select(p => new
              {
                  Id = p.PersonId,
                  Name = string.Format("{0} {1}", p.FirstName, p.LastName)
              });

尽管如此,有些查询更容易用查询语法编写,那么为什么要限制自己呢?复杂的连接在查询语法上通常更好,而且您还可以使用 SelectMany 连接格式 from ... from... join p in ... on x equals y . 有关详细信息,请参见此问题: When to prefer joins expressed with SelectMany() over joins expressed with the join keyword in Linq .

oi 是不透明标识符:

var data =  db.Persons.SelectMany(p =>  db.Companies, (p, c) => new {p,c})
    .Where(oi => oi.c.CompanyName == companyName
        && oi.p.CompanyId == oi.c.CompanyId)
    .Select(oi => oi.p)
    .Select(p => new
    {
        Id = p.PersonId,
        Name = string.Format("{0} {1}", p.FirstName, p.LastName)
    });

但是,您也可以考虑进行一些重新写入;可能是加入,或者提前移动公司名称检查;以及删除双重选择。

非顶层 从 选择多 电话:

db.Persons.SelectMany(p => db.Companies.Select(c => new { p, c }))