c# - linq 查询仅在包含 "Object reference not set to an instance of an object"时失败

Question

我有一个在 Contains 运算符上失败的 2 阶段查询连接。我得到的错误是对象引用未设置为对象的实例。我正在预先创建动态查询，并在连接中执行。

这有效:AQuery.Where("AssigneeName ==\"Michael Jackson\"")

失败并显示“对象引用未设置到对象的实例”:AQuery.Where("AssigneeName.Contains(\"Michael Jackson\")")

这是我的代码:

        using (ReqEntitiesDataContext dc = new ReqEntitiesDataContext(SPContext.Current.Web.Url))
        {

            // LINQ Deferred Query Execution
            var AQuery = from a in dc.Assignees select a;
            if (assigneeQuery.Count > 0)
            {
                AQuery = from a in AQuery.Where(string.Join(" ", assigneeQuery.ToArray())) select a;
            }

            var RQuery = from r in dc.ReqLibrary select r;
            if (requestQuery.Count > 0)
            {
                RQuery = from r in RQuery.Where(string.Join(" ", requestQuery.ToArray())) select r;
            }


            // LINQ 2 Stage Query Execution Join
            var resultQuery = from a in AQuery.ToList() 
                              join r in RQuery on a.Title equals r.RequestID
                              orderby r.RequestID ascending
                              select new RequestType
                              {
                                  RequestID = r.RequestID,
                                  ReceivedDate = r.ReceivedDate.Value,
                                  RequestType = r.RequestType,                                 
                                  Assignee = a.AssigneeName,
                                  AssigneeSection = a.AssigneeSection,
                                  AssigneeDivision = a.AssigneeDivision,
                                  RequestStatus = r.RequestStatus
                              };

            CreateTableResults(resultQuery);
        }

Answer 1

您需要处理 AssigneeName 为空的情况。