Question

var query =来自DataContext.Employees中的e 在DataContext.Dept中加入d 在e.DeptId等于d.Id 在DataContext.OtherInfo中加入o 在e.Id等于o.EmployeeId 其中e.EmployeeId == 4 选择新的Employee_Dept // DTO { EmployeeName = e.Name， DEPTNAME = d.Name 雇员= e.ID DEPTID = d.Id ContactNo = o.ContactNo }

我想用Lambda表达式编写它，这可以写 -

var query = DataContext.Employees.Join(Dept,e=>e.DeptId,d=>d.Id,(e,d)).Where(e=>e.EmployeeId=4)

任何人都可以帮我完成此查询。谢谢你的帮助。

Answer 1

我同意Craig Stuntz对Join的错误使用，但您可以通过以下方式使用扩展方法表达相同的LINQ查询：

return DataContext.Employees
         .Join(DataContext.Dept, e => e.DeptId, d => d.Id, (e,d) => new { Employee = e, Department = d })
         .Join(DataContext.OtherInfo, s => s.Employee.Id, o => o.EmployeeId, (s, o) => new { Employee => s.Employee, Department = s.Department, OtherInfo = o })
         .Where(e => e.Employee.Id == 4)
         .Select(e => select new Employee_Dept//DTO
          {
              EmployeeName=e.Employee.Name,
              DeptName=e.Department.Name
              EmployeeId=e.Employee.ID
              DeptId=e.Department.Id
              ContactNo=e.OtherInfo.ContactNo
          }

Answer 2

It's usually wrong to use join in LINQ to SQL。只需写下：

var query=from e in DataContext.Employees
          where e.EmployeeId==4 
          select new Employee_Dept//DTO
          {
              EmployeeName=e.Name,
              DeptName=d.Dept.Name
              EmployeeId=e.ID
              DeptId=d.Dept.Id
          }

如何使用Lambda表达式加入LINQ并在DTO中获取结果？

2 个答案: