Odoo function is not working

Question

This V8 code.

class project_fill_assign(models.Model):
    _inherit='project.task'

    @api.onchange('project_id')
    @api.constrains('project_id')
    def _assing_of_persons(self):
        logg = logging.getLogger(__name__)
        logg.info('Executed')

This V7 code.

_columns = { 'project_id': fields.many2one('project.project', 'Project', ondelete='set null', select=True, track_visibility='onchange', change_default=True), }