Correct Attachment Handling:

• Ensure the attachment_id parameter is processed correctly and linked to the leave request.

Upload the Attachment to ir.attachment:

• Use the ir.attachment model to store the uploaded file and link it to the leave request.

from odoo import http
from odoo.http import request

class LeavePortal(http.Controller):

    @http.route('/request', type='json', auth='user', methods=['POST'], website=True, csrf=False)
    def submit(self, leave_reason, leave_type_select_name, date_from, date_to, duration, half_day, description, request_unit_half_name, exit_entry_check, attachment_id=None):
        try:
            employee = request.env.user.employee_id
            if not employee:
                return {'error': 'Employee record not found for the current user.'}

            # Search for leave type
            leave_type = request.env['hr.leave.type'].sudo().search([
                ('name', '=', leave_type_select_name),
                ('state', '=', 'Approved')
            ], limit=1)

            if not leave_type:
                return {'error': 'Leave type not found or not approved.'}

            # Handle attachment if provided
            attach_ids = []
            if attachment_id:
                attachment = request.env['ir.attachment'].sudo().create({
                    'name': attachment_id.filename,
                    'datas': attachment_id.read(),
                    'res_model': 'hr.leave',
                    'res_id': 0,  # Temporary res_id, will be updated later
                })
                attach_ids.append(attachment.id)

            # Create leave request
            leave_data = {
                'employee_id': employee.id,
                'holiday_status_id': leave_type.id,
                'date_from': date_from,
                'date_to': date_to,
                'number_of_days': duration,
                'request_unit_half': half_day,
                'request_date_from_period': request_unit_half_name,
                'name': description,
                'request_reason': leave_reason,
                'exit_re_entry': exit_entry_check,
                'attachment_ids': [(6, 0, attach_ids)],  # Link attachments
                'create_air_ticket_request': 'no',
            }
            leave_request = request.env['hr.leave'].sudo().create(leave_data)

            # Update attachment `res_id` to link it properly
            if attach_ids:
                request.env['ir.attachment'].sudo().browse(attach_ids).write({'res_id': leave_request.id})

            return {'success': True, 'message': 'Leave request submitted successfully.'}
        
        except Exception as e:
            return {'error': str(e)}