EF寫distinct

在日常開發中常常是這么寫的

 var logErrorRequest = from l in _logErrorRepository.Table
                                      select new
                                      {
                                          WrongTime = l.WrongTime,
                                          InstitutionlGuid = l.InstitutionlGuid,
                                          DataSource = l.DataSource,
                                          AccessionNumber = l.AccessionNumber,
                                          ServiceSectID = l.ExamineType,
                                          BusinessID = l.BusinessID
                                      };
                if (query.InstitutionGuid != null)
                {
                    logErrorRequest = logErrorRequest.Where(t => t.InstitutionlGuid == query.InstitutionGuid);
                }
                if (query.LastUpdateDateStart != null)
                {
                    logErrorRequest = logErrorRequest.Where(t => t.WrongTime >= query.LastUpdateDateStart);
                }
                if (query.LastUpdateDateEnd != null)
                {
                    logErrorRequest = logErrorRequest.Where(t => t.WrongTime <= query.LastUpdateDateEnd);
                }
                var result = logErrorRequest.Distinct();

但是實際上想要

Distinct的字段只有

 InstitutionlGuid，DataSource,AccessionNumber三個字段，可是如果只查詢這三個的話下面的條件中的字段就會編譯報錯，為了只查詢這三個字段並且還能使條件的字段可以使用，可以改造成如下寫法：

    var logErrorRequest = from l in _logErrorRepository.Table
                                      select l;
                //直接寫所有字段，這樣就可以使用條件字段
                if (query.InstitutionGuid != null)
                {
                    logErrorRequest = logErrorRequest.Where(t => t.InstitutionlGuid == query.InstitutionGuid);
                }
                if (query.LastUpdateDateStart != null)
                {
                    logErrorRequest = logErrorRequest.Where(t => t.WrongTime >= query.LastUpdateDateStart);
                }
                if (query.LastUpdateDateEnd != null)
                {
                    logErrorRequest = logErrorRequest.Where(t => t.WrongTime <= query.LastUpdateDateEnd);
                }
                //在distinct的時候才會去查詢，所以這里就可以select需要distinct的字段，然后再查詢
                var result = logErrorRequest.Select(t=>new {t.InstitutionlGuid,t.DataSource,t.AccessionNumber }).Distinct();