Union Two Linq Queries

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
                                  });

问题在于我尝试联合他们。

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

即使两个单独的查询都没有，也不会返回任何记录。

Answer 1

由于2个查询似乎并不依赖于彼此，因此如果您只是尝试获取单个列表，则只执行两个查询并将每个查询的结果联合起来。

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