Odoo-Tutorial/education/models/education_class_group.py

from odoo import fields, models, api
from odoo.exceptions import ValidationError


class EductionClassGroup(models.Model):
    _name = "education.class.group"
    _description = "Education Class Group"
    _order = "sequence"
    sequence = fields.Integer(string="Sequence", default=0)
    name = fields.Char(string="Name", translate=True, required=True)
    parent_id = fields.Many2one(
        "education.class.group", string="Parent Group", ondelete="restrict"
    )
    child_ids = fields.One2many(
        "education.class.group", "parent_id", string="Child Groups"  
    )
    _parent_store = True
    _parent_name = "parent_id"
    parent_path = fields.Char(index=True)
    class_ids = fields.One2many(
        "education.class", "class_group_id", string="Class of Groups"
    )

    @api.constrains("parent_id")
    def _check_hierarchy(self):
        if not self._check_recursion():
            raise ValidationError("Error! You cannot create recursivecategories.")