转换实体框架查询中的复杂嵌套选择

Question

我需要通过此视图模型在视图中创建一个表：

public class ApplicationContentViewModel
{
    public BPMSPARS.Models.MySql.application application {get; set;}
    public BPMSPARS.Models.MySql.content content { get; set; }
    public BPMSPARS.Models.MySql.app_delegation app_delegation { get; set; }
}

但是创建新表的查询非常复杂。我在 MySQL 中使用此查询，并且使用它可以获得正确的结果。

SELECT APP_UID, (SELECT CON_VALUE FROM content WHERE CON_CATEGORY = 'PRO_TITLE' AND CON_ID = 
(SELECT PRO_UID from app_delegation WHERE del_thread_status='open' and USR_UID = '00000000000000000000000000000001' AND APP_UID = '9134216305aaaea1b67c4e2096663219')) AS TASK_NAME, 
(SELECT CON_VALUE FROM content WHERE CON_CATEGORY = 'TAS_TITLE' AND CON_ID = 
(SELECT TAS_UID from app_delegation WHERE del_thread_status='open' and USR_UID = '00000000000000000000000000000001' AND APP_UID = '9134216305aaaea1b67c4e2096663219')) AS PROCESS_NAME FROM app_delegation 
WHERE del_thread_status='open' and USR_UID = '00000000000000000000000000000001' AND APP_UID = '9134216305aaaea1b67c4e2096663219'

但是，我必须在 linq 或 MVC 中的 EF 中转换此查询。

如何在实体框架查询中编写此查询？以及如何在视图中显示结果？

Answer 1

您的SQL查询对我来说似乎(非常(奇特，因为它是多余的。我将假设子查询返回单个值并使用 LINQ 强制执行它。

首先，我在app_delegation上拉出了常见的子查询：

var USR_APP_Delegation = from a in app_delegation
                         where a.del_thread_status == "open" &&
                               a.USR_UID == "00000000000000000000000000000001" &&
                               a.APP_UID == "9134216305aaaea1b67c4e2096663219"
                         select a;

在 LINQ 中，可以轻松地将两个 UID 查询合并为一个查询：

var UIDs = (from a in USR_APP_Delegation
            select new { a.PRO_UID, a.TAS_UID })
           .Single();

现在您可以执行名称子查询：

var TASK_NAME = (from c in content
                 where c.CON_CATEGORY == "PRO_TITLE" &&
                 c.CON_ID == UIDs.PRO_UID
                 select c.CON_VALUE)
                .Single();
var PROCESS_NAME = (from c in content
                    where c.CON_CATEGORY == "TAS_TITLE" &&
                    c.CON_ID == UIDs.TAS_UID
                    select c.CON_VALUE)
                   .Single();

然后，您可以将所有查询放在一起以获得最终结果：

var ans = (from a in USR_APP_Delegation
           select new {
               a.APP_UID,
               TASK_NAME,
               PROCESS_NAME
           })
          .Single();

同样，这很明显，例如，当您确切知道它是什么时，返回APP_UID，并且您将TASK_NAME和PROCESS_NAME组合到查询中，没有真正的优势。

我建议对content使用 join 使查询更容易理解(即使在 SQL 中(，并使返回的内容更清晰：

var names = from a in app_delegation
            join cpro in content on new { CON_ID = a.PRO_UID, CON_CATEGORY = "PRO_TITLE" } equals new { cpro.CON_ID, cpro.CON_CATEGORY }
            join ctas in content on new { CON_ID = a.PRO_UID, CON_CATEGORY = "TAS_TITLE" } equals new { ctas.CON_ID, ctas.CON_CATEGORY }
            where a.del_thread_status == "open" &&
                  a.USR_UID == "00000000000000000000000000000001" &&
                  a.APP_UID == "9134216305aaaea1b67c4e2096663219"
            select new {
                a.APP_UID,
                Task_Name = ctas.CON_VALUE,
                Process_Name = cpro.CON_VALUE
            };