Question

当我返回多行时，我正试图从表tbBreadCrumb中选择BreadCrumbID的最大值。现在我将tabel tbBreadCrumb加入到表tbProjects中。如果tbBreadCrumb中有多个条目，则返回多个条目。但我只想在tbBreadCrumb中选择具有最高BreadCrumbID的行。

这是我的代码：

using (dbPSREntities5 myEntities = new dbPSREntities5())
    {
        var allDepartments = (from tbProject in myEntities.tbProjects
                              from tbBreadCrumb in myEntities.tbBreadCrumbs.Where(x => x.ProjectID == tbProject.ProjectID) <--- I want to put some sort of Max() function here where it will only slect the row with the max BreadCrumID in the table tbBreadCrumb
                              from refBreadCrumb in myEntities.refBreadCrumbs.Where(x => x.refBreadCrumbID == tbBreadCrumb.StatusID)
                              // select new anon type
                              select new
                              {
                                  ProjectID = tbProject.ProjectID,
                                  Status = refBreadCrumb.BreadCrumbValue,
                                  DateSubmitted = tbBreadCrumb.CreateDateTime,
                                  refDepartmentID = tbProject.refDepartmentID,
                                  ProjectContactFullName = tbProject.ProjectContactFirstName + " " + tbProject.ProjectContactLastName,
                                  ProjectWorkType = tbProject.ProjectWorkType,
                              });

        projectsListView.DataSource = allDepartments;
        projectsListView.DataBind();
    }

Answer 1

您可以尝试此操作，首先获取最高BreadCrumbID ID。然后在第二个查询中将其与where一起使用：

var breadId = myEntities.tbBreadCrumbs.Max(x => x.BreadCrumbID);
var allDepartments = (from tbProject in myEntities.tbProjects
                          from tbBreadCrumb in myEntities.tbBreadCrumbs.Where(x => x.ProjectID == tbProject.ProjectID && x.BreadCrumbID == breadId)
                          from refBreadCrumb in myEntities.refBreadCrumbs.Where(x => x.refBreadCrumbID == tbBreadCrumb.StatusID)
                          // select new anon type
                          select new
                          {
                              ProjectID = tbProject.ProjectID,
                              Status = refBreadCrumb.BreadCrumbValue,
                              DateSubmitted = tbBreadCrumb.CreateDateTime,
                              refDepartmentID = tbProject.refDepartmentID,
                              ProjectContactFullName = tbProject.ProjectContactFirstName + " " + tbProject.ProjectContactLastName,
                              ProjectWorkType = tbProject.ProjectWorkType,
                          });

更新：

var allDepartments = (from tbProject in myEntities.tbProjects
                          from tbBreadCrumb in myEntities.tbBreadCrumbs.Where(x => x.ProjectID == tbProject.ProjectID && x.BreadCrumbID == myEntities.tbBreadCrumbs.Where(y => y.ProjectID == tbProject.ProjectID).Max(y => y.BreadCrumbID))
                          from refBreadCrumb in myEntities.refBreadCrumbs.Where(x => x.refBreadCrumbID == tbBreadCrumb.StatusID)
                          // select new anon type
                          select new
                          {
                              ProjectID = tbProject.ProjectID,
                              Status = refBreadCrumb.BreadCrumbValue,
                              DateSubmitted = tbBreadCrumb.CreateDateTime,
                              refDepartmentID = tbProject.refDepartmentID,
                              ProjectContactFullName = tbProject.ProjectContactFirstName + " " + tbProject.ProjectContactLastName,
                              ProjectWorkType = tbProject.ProjectWorkType,
                          });

使用LINQ获取MAX（）值

1 个答案: