Hi Jenan Soliman,

Please try this code.

@api.constrains("salary_rule_id", 'amount')
def hide_some_loans(self):
    neg=[]
    for rec in self:
        if rec.salary_rule_id.name == "Net Salary" and rec.amount < 0 and rec.employee_id.name:
            neg.append(rec.employee_id.name)
    print(neg)
    if neg:
        raise ValidationError(_("Please Forward the Dedication for %s to the Next Months.") %((",".join(counterpart))))

I am not aware about the flow of your code, but try to use the "code" field of salary rule model if exist for the if condition. like 
        if rec.salary_rule_id.code == "NET" and rec.amount < 0 and rec.employee_id.name:

Hope it will help you.
Please vote up.

Hi,

Please try with this code:

@api.constrains("salary_rule_id", 'amount')
def hide_some_loans(self):
    records = self.search([])
    for rec in records:
        neg = []
        if rec.salary_rule_id.name == "Net Salary" and rec.amount < 0 and rec.employee_id.name:
            neg.append(rec.employee_id.name)
        raise ValidationError(_("Please Forward the Dedication for %s to the Next Months.") % (neg))

Thanks