c# - 合并两个 Linq 查询

Question

我有两个返回结果集的 LinqToSql 查询:

var grResults = (from g in ctx.GeneralRequests
                             join rt in ctx.RequestTypes on g.RequestTypeId equals rt.RequestTypeId
                             join sub in ctx.Logins on g.SubmitterStaffId equals sub.LoginId
                             join onb in ctx.Logins on g.OnBehalfOfStaffId equals onb.LoginId
                             where sub.GadId == gadId
                             select new
                             {
                                 Status = "Submitted",
                                 RequestId = g.GeneralRequestId,
                                 Submitter = sub.UserName,
                                 OnBehalf = (onb == null ? string.Empty : onb.UserName),
                                 RequestType = (rt == null ? string.Empty : rt.Description),
                                 ProjectName = (g == null ? string.Empty : g.ProjectName) ,
                                 Comments =  (g == null ? string.Empty :  g.Comments),
                                 LastUpdate = g.LastUpdateDate
                             });

  var grdResults = (from gd in ctx.GeneralRequestDrafts
                                  join rt in ctx.RequestTypes on gd.RequestTypeId equals rt.RequestTypeId
                                  into tempRequestTypes
                                  from rt1 in tempRequestTypes.DefaultIfEmpty()
                                  join onb in ctx.Logins on gd.OnBehalfOfStaffId equals onb.LoginId
                                  into tempOnBehalf
                                  from onb1 in tempOnBehalf.DefaultIfEmpty()
                                  join sub in ctx.Logins on gd.SubmitterStaffId equals sub.LoginId                                  
                                  where sub.GadId == gadId
                                  select new
                                  {
                                      Status = "Draft",
                                      RequestId = gd.GeneralRequestDraftId,
                                      Submitter = sub.UserName,
                                      OnBehalf = (onb1 == null ? string.Empty : onb1.UserName),
                                      RequestType = (rt1 == null ? string.Empty : rt1.Description),
                                      ProjectName = (gd.ProjectName == null ? string.Empty : gd.ProjectName),
                                      Comments = (gd.Comments == null ? string.Empty : gd.Comments),
                                      LastUpdate = gd.LastUpdateDate
                                  });

问题是当我尝试合并它们时。

 var results = grResults.Union(grdResults).OrderByDescending(r => r.LastUpdate);

这不会返回任何记录，即使两个单独的查询返回。

Answer 1

由于这 2 个查询似乎并不相互依赖，如果您只是想获得一个列表，则只需同时执行这两个查询并合并每个查询的结果。

var results = grResults.ToList().Union(grdResults.ToList())
    .OrderByDescending(r => r.LastUpdate);