What I'm trying to do:

I have a model for defining expressions that I use in a few models other models, if the expression is only numbers like 1*3 it gets the correct value. The problem becomes when I use variables like 'H' for employee hours. The models are connected with relations (not directly but trough salary).

from the model salary i can get the hours with: self.salary_data_ids.employee_id.hours

from the expressions model i can get the hours: self.salary_ids.salary_data_ids.employee_id.hours, but this is in the method that processes variables and computes the value, so it replaces the variable H with the employee hours. Expression H * 1,35 becomes 168 * 1,35 and it should return the value. 

How can I get the correct employee hours. Can I pass the self object from salary_data to the method in expressions that computes the values. Like passing an object to a method/function. Don't know if that is possible in python, but I use this in php and java. Below "code" is only an approximation of my code, only to show how the models are related.

class Salary (model.Models):

    salary_data_ids = fields.One2many()

    expressions_ids = fields.Many2many()

class Expression():

    salary_ids =  fields.Many2many()

    def compute_expression(self):

        if var == 'H':

            return self.salary_ids.salary_data_ids.employee_id.hours * 1.35

class Salary_data()

    salary_id = fields.Many2one()

    work_hours_salary = fields.Float()

   @api.multi

    def work_hours(self):

        for rec in self:

            rec.work_hours_salary = salary_id. expressions_ids.compute_expression()  

Can I pass the "rec" to the  compute_expression()  method so it can get the correct data from the correct employee and correct salary record like bellow? (record is the salary_data object)

def compute_expression(self, record):

    work_hours = record.employee_id.hours  

Or do I need to pass the salary_data.id and then use search?

def compute_expression(self, salary_data_id):

    salary_data = self.env['salary_data'].search([('id', '=', salary_data_id)])

    work_hours = salary_data.employee_id.hours

If it can be done with passing the object then my expressions don't have to be to much hard coded and any example how to do it would help a lot.