构造嵌套的 linq-to-sql 表达式以生成单个 SQL 查询

Question

我正在尝试构建我的 linq-to-sql 表达式，以便它只生成一个 SQL 数据库查询。该查询涉及两个嵌套选择，一个简化的版本是：

var query = from person in People 
            where person.ID == 1234
            select new PersonDetails() 
            {
               ID = person.ID,
               FirstName = person.FirstName,
               LastName = person.LastName,
               Addresses = from address in Addresses 
                           where address.PersonID == person.ID
                           select address
               PhoneNumbers = from number in PhoneNumbers
                              where number.PersonID == person.ID
                              select number
            }

表达式将导致执行两个 SQL 查询。第一个加入 Person 和 PhoneNumbers 表并从中提取所需的信息。第二个查询是从 Addresses 表中进行的简单选择。如果我注释掉电话号码属性，那么只会执行一个连接 Person 和 Addresses 的查询，因此 L2S 引擎确实可以识别这两种关系。

有谁知道如何构造 LINQ 表达式，以便 linq-to-sql 只生成一个 SQL 查询？

Answer 1

                        (from person in Persons
                        join address in Addresses
                        on person.id equals address.personid
                        join phone in PhoneNumbers
                        on person.id equals phone.personid
                        select new
                        {
                            Person = person,
                            Address = address,
                            Phone = phone
                        })
                       .GroupBy(p => p.Person.id)
                       .Select(g => new
                       {
                           Person = g.FirstOrDefault().Person,
                           Addresses = g.Select(k=>k.Address).Distinct(),
                           PhoneNumbers = g.Select(k=>k.Phone).Distinct()
                       });

Answer 2

您可以使用“let”关键字：

from person in context.Persons
.
.
let Add = from address in Addresses 
                           where address.PersonID == person.ID
                           select address

这是一个子查询。