Hi,

class EmployeeTravelReqest(models.Model):
    _name = 'hr.emp.travel.request'
    _description = "Travel Request"
    _inherit = ['mail.thread', 'mail.activity.mixin']

    @api.multi
    def hr_manager_user_ids_get(self):
        self.ensure_one()
        hr_group_ids = self.env.ref('hr.group_hr_manager').users.ids
        self.hr_manager_user_ids = [(6, 0, hr_group_ids)]

    user_id = fields.Many2one('res.users')
    hr_manager_user_ids = fields.Many2many('res.users', compute="hr_manager_user_ids_get")

    name = fields.Char(string="Name")
    employee_id = fields.Many2one('hr.employee', string="Employee")
    # related fields
    department_id = fields.Many2one(related="employee_id.department_id", store=True)
    company_id = fields.Many2one(related="employee_id.company_id", store=True)
    parent_id = fields.Many2one(related="employee_id.parent_id", store=True)
    job_id = fields.Many2one(related="employee_id.job_id", store=True)
    grade_id = fields.Many2one(related="employee_id.grade_id", store=True)
    currency_id = fields.Many2one(related="employee_id.company_id.currency_id", store=True)
    # Travel Dates
    from_date = fields.Date(string='From Date')
    to_date = fields.Date(string='To Date')
    expect_travel_days = fields.Integer(string="Days", compute="compute_days")
    state = fields.Selection(
        [('draft', 'Draft'), ('waiting', 'Waiting for confirmation'), ('confirmed', 'Confirmed'), ('approved', 'Approved'),
         ('closed', 'Closed'), ('rejected', 'Rejected'), ('canceled', 'Canceled')], default="draft", track_visibility="onchange")
    # travel locations
    travel_location_ids = fields.One2many('hr.emp.travel.location', 'travel_request_id_ref', required=True)
    total_travel_days = fields.Integer(string="Days", compute="compute_days_travel_location")
    # Expenses(proposed/actual)
    expense_amount_ids = fields.One2many('hr.expense.amount', 'travel_request_id')
    total_expense_amount = fields.Monetary(string="Grand Total", compute="compute_total_expense_amount", store=False)
    ticket_book = fields.Boolean(string="Company Books ticket for You", track_visibility="onchange")
    # Log
    request_by = fields.Many2one('res.users', default=lambda self: self.env.uid)
    approved_by = fields.Many2one('res.users')
    rejected_by = fields.Many2one('res.users')
    request_date = fields.Date(string="Requested Date", default=date.today())
    approved_date = fields.Date()
    rejected_date = fields.Date()
    reject_reason = fields.Char("Reason For Reject")
    # Reason
    reason = fields.Text(string="Reason")
    # Currency
    currency_ids = fields.One2many('hr.travel.currency', 'travel_request_id')

    # Expenses    expenses_ids = fields.One2many('hr.expense', 'travel_request_id_ref'

@api.multi
def action_send_manager(self):
    for rec in self:
        if not rec.travel_location_ids:
            raise Warning("Please enter the travel information before submit to manager")
        else:
            rec.state = 'waiting'

I get this error when I try to save more than one line in one2many field.

Thank you in advance for any help.