I am developing a custom module that adds a team of users to task. I've based my code on project.task.work model.

Here is my code for the team:

class paga_task_team(osv.Model):
    _name = 'paga_task_team'

    _columns = {
        'paga_task_id': fields.many2one('project.task', string="Task", ondelete="set null", select="1"),
        'paga_user_id': fields.many2one('res.users','User', required=True),
        'paga_booking': fields.selection(
            (('OK','OK'),
            ('UN','Pending'),
            ('NO','Declined')),
            'Booking'),
        'paga_mail': fields.boolean('Mail?'),
        'paga_sms': fields.boolean('SMS?'),
    }

    _default = {
        'paga_booking': 'UN',
        'paga_mail': False,
        'paga_sms': False,
        }

paga_task_team()

And this parts extends the project.task

class paga_task_booking(osv.Model):

    _name = "project.task"
    _inherit = ["project.task", "mail.compose.message"]

    _columns = {
        'date_deadline': fields.datetime('Deadline',select=True),
        'paga_task_duration': fields.float('Duration'),
        'paga_team_size': fields.integer('Team Size'),
        'paga_team_ids': fields.one2many('paga_task_team','paga_task_id','Team', 
        states={'close':[('readonly',True)], 'cancelled':[('readonly',True)]}),
    }

paga_task_booking()

These codes only works if I make paga_task_team into a TransientModel, but then the datas are not saved permanently. If it is cvs.Model I get the error "Many2One relationships from non-transient Model to TransientModel are forbidden". I cannot see what is wrong, since this should be quite simple structure...