C# linq linq-query-syntax linq-to-dataset

在 C# 中使用查询语法时，“枚举未产生结果”。如何检索输出

发布于 2024-09-03 03:56:07 字数 953 浏览 1 评论 0原文

我创建了这个查询来从数据库中获取一些结果。这是我的表结构< /a>.

到底发生了什么。

DtMapGuestDepartment如表1
Dt部门如表2
正在使用

    var dept_list=  from map in DtMapGuestDepartment.AsEnumerable()
                    where map.Field<Nullable<long>>("GUEST_ID") == DRowGuestPI.Field<Nullable<long>>("PK_GUEST_ID")
                    join 
                    dept in DtDepartment.AsEnumerable()
                    on map.Field<Nullable<long>>("DEPARTMENT_ID") equals dept.Field<Nullable<long>>("DEPARTMENT_ID")
                    select dept.Field<string>("DEPARTMENT_ID");

我正在执行此查询 DataTables 并期望它返回我数据表。

在这里，我想从表 1 中选择不同的部门，这将是我的下一个任务。如果可能的话也请回答这个问题。

原文

I have created this query to fetch some result from database.
Here is my table structure.

What exaclty is happening.

DtMapGuestDepartment as Table 1
DtDepartment as Table 2
Are being used

    var dept_list=  from map in DtMapGuestDepartment.AsEnumerable()
                    where map.Field<Nullable<long>>("GUEST_ID") == DRowGuestPI.Field<Nullable<long>>("PK_GUEST_ID")
                    join 
                    dept in DtDepartment.AsEnumerable()
                    on map.Field<Nullable<long>>("DEPARTMENT_ID") equals dept.Field<Nullable<long>>("DEPARTMENT_ID")
                    select dept.Field<string>("DEPARTMENT_ID");

I am performing this query on
DataTables and expect it to return me
a datatable.

Here I want to select distinct department from Table 1 as well which will be my next quest. Please answer to that also if possible.

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可是我不能没有你 2024-09-10 03:56:07

将查询分成几部分，看看哪个集合没有元素。

var mapList = DtMapGuestDepartment.AsEnumerable().ToList();
var deptList = DtDepartment.AsEnumerable().ToList();

var queryResult1 = (
  from map in mapList
  where map.Field<Nullable<long>>("GUEST_ID") ==
    DRowGuestPI.Field<Nullable<long>>("PK_GUEST_ID") 
  select map
).ToList();

var queryResult2 = (
  from map in queryResult1
  join dept in deptList
    on map.Field<Nullable<long>>("DEPARTMENT_ID")
    equals dept.Field<Nullable<long>>("DEPARTMENT_ID") 
  select dept.Field<string>("DEPARTMENT_ID")
).ToList();

break your query into parts and see which collection has no elements.

var mapList = DtMapGuestDepartment.AsEnumerable().ToList();
var deptList = DtDepartment.AsEnumerable().ToList();

var queryResult1 = (
  from map in mapList
  where map.Field<Nullable<long>>("GUEST_ID") ==
    DRowGuestPI.Field<Nullable<long>>("PK_GUEST_ID") 
  select map
).ToList();

var queryResult2 = (
  from map in queryResult1
  join dept in deptList
    on map.Field<Nullable<long>>("DEPARTMENT_ID")
    equals dept.Field<Nullable<long>>("DEPARTMENT_ID") 
  select dept.Field<string>("DEPARTMENT_ID")
).ToList();

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