old_contents: ##############################################################################
  # For copyright and license notices, see __manifest__.py file in module root
  # directory
  ##############################################################################
  from odoo import models, fields, api
  
  
  class ProductTemplate(models.Model):
  
      _inherit = "product.template"
  
      force_currency_id = fields.Many2one(
          'res.currency',
          'Force Currency',
          help='Use this currency instead of the product company currency'
      )
      company_currency_id = fields.Many2one(
          related='company_id.currency_id')
  
      @api.depends(
          'force_currency_id',
          'company_id',
          'company_id.currency_id')
      def _compute_currency_id(self):
          super(ProductTemplate, self)._compute_currency_id()
          for rec in self.filtered('force_currency_id'):
              rec.currency_id = rec.force_currency_id
  
new_contents: ##############################################################################
  # For copyright and license notices, see __manifest__.py file in module root
  # directory
  ##############################################################################
  from odoo import models, fields, api
  
  
  class ProductTemplate(models.Model):
  
      _inherit = "product.template"
  
      force_currency_id = fields.Many2one(
          'res.currency',
          'Force Currency',
          help='Use this currency instead of the product company currency',
      )
      company_currency_id = fields.Many2one(
          related='company_id.currency_id',
          readonly=True,
      )
  
      @api.depends(
          'force_currency_id',
          'company_id',
          'company_id.currency_id')
      def _compute_currency_id(self):
          super(ProductTemplate, self)._compute_currency_id()
          for rec in self.filtered('force_currency_id'):
              rec.currency_id = rec.force_currency_id
  
subject: add readonly attribute to company_currency_id field becase appear an error when create a product (#174)