how to insert(if not exsit) or update (if exsit) a one2many field and always limit the row in one record

for exemple

class vente(models.Models):

    _name = 'vente'

    def calcul_recette(self):

        // ......

    recette = fields.Float('recettre du jour', compute='calcul_recette')

    date = fields.Date('date')

    ligne_recette = fields.One2many('caisse', 'rec_id', 'caisse')

    for rec in self.env['caisse'].search([()]):

        rec.create({'date': self.ate, 'recette': self.recette, 'depense': 0})

        #this is what i now but it doesn't work as ... insert(if not exsit) or update (if exsit) a one2many field and        always limit the row in one record .....

class caisse(models.Models):

    _name = 'caisse'

    depense = fields.Float('depense')

    recette = fields.Float('recette')

    date = fields.Date('date')

    rec_id = fields.Many2one('vente', 'rec_id')