Linq 联合两个表，其中有一个额外的列

Question

我正在使用 Union 来组合两个 tables audit 和 message。它们都有相同的列名，除了 audit 有一个名为 deleteDate 的额外列。我尝试使用 Union 合并两个 table，如果 deleteDate 不存在，则将 DeleteDate 方法设置为 null。我评论了我想要开始工作的内容。当我取消注释代码时，出现错误。有解决办法吗？这是我的代码

    var audit = from a in _Audit.GetAll()
                       .Where(a => a.PInt == pInt && a.CreateDate < startDate && (endDate == null || endDate > a.CreateDate))
                       select new
                       {
                           a.MInt,
                           a.MId,
                           a.Desc,
                           a.PString,
                           a.PType,
                           a.MType,
                           a.CreateDate,
                           //    a.DeleteDate,
                           a.PInt
                       };

    var message = from a in _Message.GetAll()
           .Where(a => a.PartnerInt == partnerInt && a.CreateDate < startDate && (endDate == null || endDate > a.CreateDate))
                  select new
                  {
                      a.MInt,
                      a.MId,
                      a.Desc,
                      a.PString,
                      a.PType,
                      a.MType,
                      a.CDate,
                      a.PInt
                  };

    var test = from a in audit.Union(message)
               select new AuditMessagesGroup
               {
                   MInt = a.Int,
                   MId = a.Id,
                   Desc = a.Desc,
                   PString = a.PString,
                   PType = a.PayloadType,
                   MessageType = a.MType,
                   CreateDate = a.CreateDate,
         //          DeleteDate = a.DeleteDate != null ? a.DeleteDate : null,
                   PInt = a.PInt

               };

这里是错误

    Error   CS1929  'IQueryable<<anonymous type: int MInt, Guid 

MId, string Desc, string PString, string PType, 

MTypes MType, DateTime CreateDate, DateTime DeleteDate, int? 

PInt>>' does not contain a definition for 'Union' and the best 

extension method overload 'ParallelEnumerable.Union<<anonymous type: int 

MInt, Guid MId, string Desc, string PString, string 

PType, MTypes MType, DateTime CreateDate, int? PInt>>

(ParallelQuery<<anonymous type: int MInt, Guid MId, string 

Desc, string PString, string PType, MTypes 

MType, DateTime CreateDate, int? PInt>>, IEnumerable<<anonymous 

type: int MInt, Guid MId, string Desc, string 

PString, string PType, MTypes MType, DateTime 

CreateDate, int? PInt>>)' requires a receiver of type 

'ParallelQuery<<anonymous type: int MInt, Guid MId, string 

Desc, string PString, string PType, MTypes 

MType, DateTime CreateDate, int? PInt>>'

Answer 1

不，你不能。联合的基本标准是列数必须匹配 b/w 个表。您可以生成一个虚拟列来绕过。喜欢

考虑 a.DeleteDate 在 audit 中 DateTime 将您的 message 更改为

var message = from a in _Message.GetAll()
       .Where(a => a.PartnerInt == partnerInt && a.CreateDate < startDate && (endDate == null || endDate > a.CreateDate))
              select new
              {
                  a.MInt,
                  a.MId,
                  a.Desc,
                  a.PString,
                  a.PType,
                  a.MType,
                  a.CDate,
                  DateTime.Now, // a dummy column
                  a.PInt
              };

然后你可以执行 UNION

Answer 2

要使 .Union(...) 工作，匿名类型必须完全相同 - 这要求它具有完全相同的字段数和完全相同的类型, 具有完全相同的名称。

因此，根据您的查询，我认为您需要这个：

var audit =
    from a in _Audit
        .GetAll()
        .Where(a => a.PInt == pInt)
        .Where(a => a.CreateDate < startDate)
        .Where(a => endDate == null || endDate > a.CreateDate)
    select new
    {
        a.MInt,
        a.MId,
        a.Desc,
        a.PString,
        a.PType,
        a.MType,
        a.CreateDate,
        a.DeleteDate,
        a.PInt
    };

var message =
    from a in _Message
        .GetAll()
        .Where(a => a.PartnerInt == partnerInt)
        .Where(a => a.CreateDate < startDate)
        .Where(a => endDate == null || endDate > a.CreateDate)
    select new
    {
        a.MInt,
        a.MId,
        a.Desc,
        a.PString,
        a.PType,
        a.MType,
        CreateDate = a.CDate,
        DeleteDate = (DateTime?)null,
        a.PInt
    };

我无法确定每种 table 的类型，但希望它们非常接近。

您可能需要使用 .ToArray() 将记录拉入内存，然后使用新的 .Select(...) 以使字段类型对齐，但假设它们已经相同它应该可以正常工作。

Linq 联合两个表，其中有一个额外的列

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c#

linq

union