Question

我想通过合并来自ViewModel中两个表的数据来绑定下拉列表。你能否澄清一下我该怎么做？例如，我想在一行中的2个表中显示4个字段，如下所示：

MeetingName / MeetingCityIdA的名称 / MeetingCityIdB的名称 / MeetingDate

以下是我使用的实体：

会议

public int MeetingID { get; set; }
public string MeetingName { get; set; }
public DateTime MeetingDate { get; set; }
public int? MeetingCityIdA { get; set; }
public int? MeetingCityIdB { get; set; }
public int? MeetingCityIdC { get; set; }

的城市：

public int CityID { get; set; }
public string CityName { get; set; }

的视图模型：

public class ViewModel
{
    public Applicant Applicant { get; set; }
    public IEnumerable<Applicant> Applicants { get; set; }

    public IEnumerable<Meeting> Meetings { get; set; }
    public IEnumerable<City> Cities { get; set; }
}

的型号：

Answer 1

您可以使用下一个linq查询：

var list = Meetings.GroupJoin(Cities, m => m.MeetingCityIdA, c => c.CityID, (m, c) => new {m, cA = c.DefaultIfEmpty()})
                .SelectMany(z => z.cA.Select(cA => new { m = z.m, cA })
                .GroupJoin(Cities, m => m.m.MeetingCityIdB, c => c.CityID, (m, c) => new {m.m, m.cA, cB = c.DefaultIfEmpty()})
                .SelectMany(z => z.cB.Select(cB => new { m = z.m, cA= z.cA, cB })
                .GroupJoin(Cities, m => m.m.MeetingCityIdC, c => c.CityID, (m, c) => new {m.m, m.cA, m.cB, cC = c.DefaultIfEmpty()})
                .SelectMany(z => z.cC.Select(cC => new { m = z.m, cA= z.cA, cB = z.cB, cC })
                .Select(
                    m =>
                        new
                        {
                            m.m.MeetingName,
                            NameofMeetingCityIdA = m.cA!=null?m.cA.CityName:null,
                            NameofMeetingCityIdB = m.cB!=null?m.cB.CityName:null,
                            NameofMeetingCityIdC = m.cC!=null?m.cC.CityName:null,
                            m.m.MeetingDate
                        });

它在MeetingCityIdA上加入与Cities的会议，然后将结果连接到MeetingCityIdB上的Cities，然后选择你想要的内容。

但是，如果您将实体的导航属性用于而不是使用来自linq的Join语句，那将是正确的。

Answer 2

@Kirill Bestemyanov的更新和工作答案：

var list = repository.Meetings
    .GroupJoin(repository.Cities, m => m.MeetingCityIdA, c => c.CityID, (m, c) => new {m, cA = c.DefaultIfEmpty()})
    .SelectMany(z => z.cA.Select(cA => new { m = z.m, cA }))
    .GroupJoin(repository.Cities, m => m.m.MeetingCityIdB, c => c.CityID, (m, c) => new {m.m, m.cA, cB = c.DefaultIfEmpty()})
    .SelectMany(w => w.cB.Select(cB => new { m = w.m, cA= w.cA, cB }))
    .GroupJoin(repository.Cities, m => m.m.MeetingCityIdC, c => c.CityID, (m, c) => new {m.m, m.cA, m.cB, cC = c.DefaultIfEmpty()})
    .SelectMany(t => t.cC.Select(cC => new { m = t.m, cA= t.cA, cB = t.cB, cC }))
    .Select(
        m =>
            new
            {
                m.m.MeetingName,
                NameofMeetingCityIdA = m.cA!=null?m.cA.CityName:null,
                NameofMeetingCityIdB = m.cB!=null?m.cB.CityName:null,
                NameofMeetingCityIdC = m.cC!=null?m.cC.CityName:null,
                m.m.MeetingDate
            });

使用Lambda Expression在ViewModel中连接两个表

2 个答案: