在Doctrine 2中设置列别名时出错

Question

I am using Doctrine 2.3.3 as ORM in my project. Everything is running smooth and fine. Now i want to give my column names my own aliases. I've read in the documentation of doctrine 2 that the following code is the way to give aliases.

<?php
/**
 * @Entity(repositoryClass="Entity\Repositories\EmployeeRepository")
 * @Entity @Table(name="tbl_employee")
 */
class TblEmployee
{
    /** @Id @Column(name="employee_id",type="string",length=45) */
    public $emid;

    //getters

    public function getEmId()
    {
        return $this->emid;
    }

    //setters

    public function setEmployeeId($emid)
    {
        $this->emid = $emid;
    }

?>

but when i execute this code I get the error

[Semantical Error] line 0, col 36 near 'employee_id <': Error: Class TblEmployee has no field or association named employee_id

how do i solve this?? or what is the correct way to give aliases to the columns??