Question

在1个查询中，我想选择2个表（Union）的结果。

表1： StationStatus

表2： DetectorStatus

我可以执行以下查询：

SELECT TOP 1000 [DetectorStatusID],
      [DetectorID],
      [DateTime],
      [DetectorModeID],
      NULL as StationModeID,
      [Status]
  FROM [GMS_MAN].[dbo].[DetectorStatus] 
  UNION SELECT TOP 1000 [StationStatusID],
      [DetectorID],
      [DateTime],
      NULL as DetectorMOdeID,
      [StationModeID],
      [Status] FROM [GMS_MAN].[dbo].StationStatus 
ORDER BY Status

这将导致2个表合并为1。

但是，我不知道如何在代码中执行此操作我当前正在执行的查询仅适用于 DetectorStatus表

    [Query]
[OutputCache(OutputCacheLocation.Server, 60)]
public IQueryable<DetectorStatu> GetDatabacklog(int userID)
{
    User user = ObjectContext.Users
        .Include("TeamMemberships")
        .First(u => u.UserID == userID);

    var teamIDs = user.TeamMemberships.Select(t => t.TeamID).ToList();
    var siteIDs = ObjectContext.SiteMemberships.Where(t => teamIDs.Contains(t.TeamID)).Select(t => t.SiteID).ToList();
    var DetectorStatus =  ObjectContext.DetectorStatus
        .Include("Detector")
        .Include("Detector.Track")
        .Include("Detector.Site")
        .Include("Detector.EnabledDetectorTypes")
        .Include("Detector.EnabledDetectorTypes.DetectorType")
        .Where(d => siteIDs.Contains(d.Detector.SiteID))
        .OrderBy(d => d.Status);

    return DetectorStatus;
}

我称之为：

private void GetDatabacklog()
{
    LoadOperation<DetectorStatu> loadOp = context.Load(context.GetDatabacklogQuery(App.CurrentUser.UserID), LoadBehavior.RefreshCurrent, LoadDatabacklogCompleted, null);
}

private void LoadDatabacklogCompleted(LoadOperation<DetectorStatu> loadOperation)
{
    //The rest of the code where i show the results.
}

我的问题，如何在多个表格中使用它？因为在查询中我需要调用 StationStatu 和 DetectorStatu ，但我不知道如何执行此操作。

当我向任何内容添加.Union时，我收到以下错误：

我正在使用的代码：

var detectorSt = ObjectContext.DetectorStatus.Select(x => new { x.DetectorID, x.Status});
var stationSt = ObjectContext.StationStatus.Select(x => new { x.DetectorID, x.Status}); 
var unioned = detectorSt.Union(stationSt);
return unioned;

Answer 1

我无法在单个查询中查看来自两个表的数据的任何理由，而无需以任何方式链接结果。因此，我建议您分别查询表，将它们选择为公共数据对象并将它们合并到客户端而不是服务器端（如果需要，您仍然可以在服务器上对查询进行排序，然后只在客户端合并已排序的数据）。

public class StatusTransferObject
{
    public int DetectorId { get; set; }
    public DateTimeOffset DateTime { get; set; }
    public int? DetectorModeId { get; set; }
    public int? StationModeId { get; set; }
    public decimal Status { get; set; }
}

var orderedObjects1 = ObjectContext.DetectorStatus.OrderBy(s => s.Status).Select(s => new StatusTransferObject
{
    DetectorId = s.DetectorID,
    DateTime = s.DateTime,
    DetectorModeId = s.DetectorModeID,
    StationModeId = null,
    Status = s.Status
});
var orderedObjects2 = ObjectContext.StationStatus.OrderBy(s => s.Status).Select(s => new StatusTransferObject
{
    DetectorId = s.DetectorID,
    DateTime = s.DateTime,
    DetectorModeId = null,
    StationModeId = s.StationModeID,
    Status = s.Status
});
var mergedObjects = MergeSorted(orderedObjects1, orderedObjects2, (x1, x2) => x1.Status.CompareTo(x2.Status)).ToList();

MergeSorted取自以下问题：Is there an easy way to merge two ordered sequences using LINQ?

C＃Linq从多个表中选择数据

1 个答案: