Model for hasOne foreign key issues

[zorrofox]

I have one table employee have one foreign key with other table department, and the table column and data below:
For empoyee

employee_id	employee_name	department_id
1	Tom Preston-Werner	1
2	Albert Einstein	1

For department

department_id	department_name
1	Department1
2	Department2

I have this model define and query below:

...
department = persist.define('department', {
    'id' : {
        type : type.INTEGER,
        dbColumnName : 'department_id',
        primaryKey : true
    },
    'department_name' : type.STRING
});

employee = persist.define('employee', {
    'id' : {
        type : type.INTEGER,
        dbColumnName : 'employee_id',
        primaryKey : true
    },
    'employee_name' : type.STRING
}).hasOne(department);

persist.connect({
    "driver" : "oracle",
    "hostname" : "localhost",
    "user" : "hr",
    "password" : "welcome1",
    trace : true
}, function(err, connection) {
    employee.include('department').all(connection, function(err, employees) {
        if(err)
              console.log(err);     
    });

});
...

But the ORM will return this SQL to me:

select t0.employee_id AS c0,
 t0.employee_name AS c1,
 t0.department_id AS c2,
 t1.department_id AS c3,
 t1.department_name AS c4 
FROM employees t0 
LEFT JOIN departments t1 ON t1.employee_id=t0.department_id  

It is very stange the ORM will use the employee_id as the join key. Anyone also has this issue?