c#如何用sql填充包含列表的复杂对象

Question

我目前有一个使用实体框架的对象模型，其中包含一个具有列表属性的复杂对象。我使用此处提出的第二个选项将其存储在数据库中：Representing a list in a SQL database

但总结一下：

Person()
{
  long Id;//primary key
  string Name;
  List<long> ResponsibleFor; //list of id    
}

存储为以下 2 个表格

Persons:
 Id,
 Name

Responsibilities:
 Id,
 PersonId,
 ResponsibleForId

现在我有点不知道如何重新填充 Person 对象。我目前的方法如下：

 from p in db.Persons
 join r in db.Responsibilities on p.Id equals r.PersonId
 where p.Id == IdImSearchingFor
 select new Person
 {
  Id = p.Id
  ResponsibileFor = ?
 }

我一直在尝试重新填充该 List 属性。

有什么建议吗？

谢谢！

Answer 1

你需要对加入的结果进行分组，让所有人负责。

试试

var result = from p in db.Persons
             join r in db.Responsibilities on p.Id equals r.PersonId
             where p.Id == IdImSearchingFor
             group r.ResponsibleForId by p into g
             select new Person 
             {
                 Id = g.Key.Id, 
                 Name = g.Key.Name,
                 ResponsibleFor = g.ToList()
             };

Answer 2

假设您想获取 ID 为 1 的人员..

from p in db.Persons
 join r in db.Responsibilities on p.Id equals r.PersonId
 where p.Id == 1
 select new Person
 {
  Id = p.Id
  ResponsibileFor = p.ReponsibleFor 
}

Answer 3

看看这个。我已经测试过它是普通的类和列表，而不是 EF 或任何其他 ORM。

以下是我理解的类结构

class Person
{
    public long Id;//primary key
    public string Name;
}

class Responsibility
{
    public long Id;//primary key
    public long PersonId;
    public long ResponsibleForId; 
}

以下是2个测试列表

List<Person> Persons = new List<Person>() { new Person() { Id = 1, Name = "Samar" } };
List<Responsibility> Responsibilities = new List<Responsibility>() { new Responsibility() { Id = 1, PersonId = 1, ResponsibleForId = 1 }, new Responsibility() { Id = 2, PersonId = 1, ResponsibleForId = 2 } };

以下是查询

var allPeople = from p in Persons
                join r in Responsibilities on p.Id equals r.PersonId into g
                where p.Id == 1
                select new
                {
                    Id = p.Id,
                    ReponsibleFor = g.Select(x => x.ResponsibleForId).ToList()
                };

希望这是您正在寻找的。​​p>

Answer 4

虽然每个人之前的回答都对我有所帮助（谢谢！），但他们并没有完全发挥作用。所以我想我应该在这里添加我的解决方案，即使用连接、分组和嵌套选择的组合。

from p in db.Persons
where p.Id == IdImSearchingFor
join r in db.Responsibilities on p.Id equals r.ParentId into pr
select new Person
{
    Id = p.Id,
    name = p.Name,
    ResponsibleFor = ( from a in pr
                       where a.ParentId == IdImSearchingFor
                       select new Person
                       {
                           Id = a.Id
                       }).ToList<Person>()
}

Answer 5

我的建议是使用延迟加载模式来获取您的列表，它可能会更好地执行和扩展。用你的例子。

public class Person()
{
  public long Id { get; set; }
  public string Name { get; set;}
  private Lazy<List<long>> _responsibleFor;
  public List<long> ResponsibleFor
  {
    get { return _responsibleFor.Value; }
  }

  public void SetResponsibleFor(Func<long, List<long>> getResponsibleFor)
  {
    _responsibleFor = new Lazy<List<long>>( () => getResponsibleFor(Id) );
  }

  public Person():base() { }
  public Person(long id, string name)
  {
    Id = id;
    Name = name
  }

}

   // Implementation
   var p = new Person(1,"John Doe");
   p.SetResponsibleFor(GetResponsibleForPerson); //Pass a function/method which takes the long for input parameter and outputs List<long>