LINQ to 实体和对象查询

Question

我的 Person 实体与 Person_Addresses 有 1 : N 的关系（字段：PersonID、AddressID、ValidFrom）。我想获取所有Person 记录和关联的Person_Addresses，只有最新的ValidFrom。我应该如何使用 ObjectQuery 或 IQueryable 来做到这一点？

编辑： 我提到了ObjectQuery 和IQueryable，因为我想有一个使用扩展方法的解决方案（我认为，它是如何被调用的）。另外我忘了提到我正在使用Entity Framework 来生成实体。我想得到一个 person 对象，它的 person_adress 成员急切地加载。

以下是实体结构： 个人成员：int id, string firstname, string lastname, Partner_Address partneradress

Person_Address 成员：int personid、int adressid、date validfrom

Answer 1

试试下面的。

我有以下实体。

    //Person Entity
    public class Person
    {
        public int PersonID  { get; set; }
        public string PersonName { get; set; }
    }

    //PersonAddress Entity
    public class PersonAddress
    {
        public int PersonID { get; set; }
        public int AddressID { get; set; }
        public DateTime ValidFrom { get; set; }
    }

然后触发以下查询。

    //Get the latest ValidFrom for each person from PersonAddress.
    var getLatestDateRecords =
    from p in lstPersonAddress
    group p by p.PersonID into g
    select new
    {
        Infos =
            (from PA in g
            select new
            {
                PersonId = PA.PersonID
                Date = g.Max(t=>t.ValidFrom)
            }).Distinct()
    };

    //Segregate the ValidFroms and PersonId from the
    //previous record set(getLatestDateRecords).
    var segRecords =
        from x in getLatestDateRecords
        from y in x.Infos
        select new { Date = y.Date, PersonId = y.PersonId };

    //Obtain all the relevant information from the PersonAddress
    // for the latest ValidFrom dates.
    var allValidRecords =
        from PA in lstPersonAddress
        join x in segRecords
        on PA.ValidFrom equals x.Date
        where PA.PersonID == x.PersonId
        select new {
                PersonId = PA.PersonID
                , AddressId = PA.AddressID
                , Date = PA.ValidFrom
            };

    //Get the final result
    var resultSet =
        from p in lstPerson
        join x in allValidRecords
        on p.PersonID equals x.PersonId
        select new
        {
            PersonId = p.PersonID
            ,PersonName = p.PersonName
            ,AddressId = x.AddressId,
            Date = x.Date
        };

我发现它可以很好地处理一些测试数据。

如有任何疑问，请告诉我。