odoo_18_Education_management/models/school_subject_lesson.py

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

class SchoolSubjectLesson(models.Model):
    _name = 'school.subject.lesson'
    _description = 'Subject Lesson Plan'

    subject_id = fields.Many2one('school.subject', string='Subject', ondelete='cascade', required=True)
    title = fields.Char(string='Title', required=True)
    prepared_by = fields.Many2one('res.users', string='Prepared By')
    period = fields.Char(string='Timing Period')  # e.g. 10:00 AM - 11:00 AM
    total_lessons = fields.Integer(string='Total Lessons', default=1)

    teacher = fields.Many2one('res.users', string='Teacher')
    class_id = fields.Many2one('school.class', string='Class')

    activity_count = fields.Integer(
        string="No. of Activities",
        compute="_compute_activity_count",
        store=False
    )

    @api.depends('subject_id')
    def _compute_activity_count(self):
        for record in self:
            record.activity_count = len(record.subject_id.teacher_info_line_ids)