Hi,

Odoo ORM doesn’t support One2one fields, but you can do them manually. In the example below we make one2one relationship between models hr.recruitment.stage and hr.job.
In short, you set normal Many2one field (stage_id in the example) in a one model (doesn’t really matter which of the models you choose) and corresponding One2many field (stage_ids in the example) in another model. Then we add virtual Many2one field (job_id in the example) with attributes compute and inverse.

class HrRecruitmentStage(models.Model):
    _name = 'hr.recruitment.stage'
    job_id = fields.Many2one('hr.job', compute='compute_stage', inverse='stage_inverse')
    stage_ids = fields.One2many('hr.job', 'stage_id')

    @api.depends('stage_ids')
    def compute_stage(self):
        if len(self.stage_ids) > 0:
            self.job_id = self.stage_ids[0]

    def stage_inverse(self):
        if len(self.stage_ids) > 0:
            # delete previous reference
            stage = self.env['hr.job'].browse(self.stage_ids[0].id)
            asset.stage_id = False
        # set new reference
        self.job_id.stage_id = self


class HrJob(models.Model):
    _name = 'hr.job'
    stage_id = fields.Many2one('hr.recruitment.stage', string='Stage')

Hope it helps