来自对象的LINQ Left Join

Question

我有一个linq查询，当我连接两个表时工作正常，但当我包含另一个表时，它不返回数据。请帮我弄清楚我做错了什么。

First Linq返回数据：

var q = (from c in _context.Complaint
        join cl in _context.Checklist on c.COMP_ID equals cl.COMP_ID into clleft
        from cls in clleft.DefaultIfEmpty()
        orderby c.timestamp descending
        select new
         {
          FileNum = c.FileNum
         }).AsQueryable().Distinct();

         return q;

当我添加此表时，没有数据返回

var q = (from c in _context.Complaint
        join cl in _context.Checklist on c.COMP_ID equals cl.COMP_ID into clleft
        from cls in clleft.DefaultIfEmpty()
        join oim in _context.OIM_EMPLOYEE on cls.MonitorEnteredEmpID equals oim.EmpID into oimleft
        from oims in oimleft.DefaultIfEmpty()
        orderby c.timestamp descending
        select new
              {FileNum = c.FileNum
              }).AsQueryable().Distinct();

        return q;