LINQ到Entites和ObjectQuery

Question

我有Person实体，它与Person_Addresses有1:n的关系(字段：PersonID、AddressID、ValidFrom)。我想得到所有的Person记录和相关的Person_Addresses，只有最新的ValidFrom。我应该如何使用ObjectQuery或IQueryable来完成这个任务？

编辑：，我提到了ObjectQuery和IQueryable，因为我希望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)。此外，我忘了提到我使用的是生成实体的实体框架。我想得到一个person对象，它有它的person_adress成员。

以下是实体结构: Person成员: int id、字符串名、字符串姓氏、Partner_Address partneradress

Person_Address成员：int personid，int adressid，date validfrom

Answer 1

试试看以下几点。

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
        };

我发现它在一些测试数据中运行良好。

如果有任何问题，请告诉我。