<h1>Model constraints</h1>

Model constraints
Odoo provides two ways to set up automatically verified invariants: Python constraints and SQL constraints.

A Python constraint is defined as a method decorated with constrains(), and invoked on a recordset. The decorator specifies which fields are involved in the constraint, so that the constraint is automatically evaluated when one of them is modified. The method is expected to raise an exception if its invariant is not satisfied:

from openerp.exceptions import ValidationError

@api.constrains('age')
def _check_something(self):
    for record in self:
        if record.age > 20:
            raise ValidationError("Your record is too old: %s" % record.age)
    # all records passed the test, don't return anything

Add a constraint that checks that the instructor is not present in the attendees of his/her own session.

openacademy/models.py

# -*- coding: utf-8 -*-

from openerp import models, fields, api, exceptions

class Course(models.Model):
    _name = 'openacademy.course'

                    'message': "Increase seats or remove excess attendees",
                },
            }

    @api.constrains('instructor_id', 'attendee_ids')
    def _check_instructor_not_in_attendees(self):
        for r in self:
            if r.instructor_id and r.instructor_id in r.attendee_ids:
                raise exceptions.ValidationError("A session's instructor can't be an attendee")


SQL constraints are defined through the model attribute _sql_constraints. The latter is assigned to a list of triples of strings (name, sql_definition, message), where name is a valid SQL constraint name, sql_definition is a table_constraint expression, and message is the error message.


    CHECK that the course description and the course title are different

    Make the Course's name UNIQUE

openacademy/models.py

    session_ids = fields.One2many(
        'openacademy.session', 'course_id', string="Sessions")

    _sql_constraints = [
        ('name_description_check',
         'CHECK(name != description)',
         "The title of the course should not be the description"),

        ('name_unique',
         'UNIQUE(name)',
         "The course title must be unique"),
    ]


class Session(models.Model):
    _name = 'openacademy.session'

Add a duplicate option

Since we added a constraint for the Course name uniqueness, it is not possible to use the "duplicate" function anymore (Form ‣ Duplicate).

Re-implement your own "copy" method which allows to duplicate the Course object, changing the original name into "Copy of [original name]".

openacademy/models.py

    session_ids = fields.One2many(
        'openacademy.session', 'course_id', string="Sessions")

    @api.multi
    def copy(self, default=None):
        default = dict(default or {})

        copied_count = self.search_count(
            [('name', '=like', u"Copy of {}%".format(self.name))])
        if not copied_count:
            new_name = u"Copy of {}".format(self.name)
        else:
            new_name = u"Copy of {} ({})".format(self.name, copied_count)

        default['name'] = new_name
        return super(Course, self).copy(default)

    _sql_constraints = [
        ('name_description_check',
         'CHECK(name != description)',