anchor.diff:  duration and a number of seats. Although we could have used the same file
   we will create a new file for sessions to organise our code.
   
  -NOTE: Don't forget to run `hexya generate` after creating the new model
  +NOTE: Don't forget to run `hexya generate` and `hexya updatedb` after creating
  +the new model
   
   .openacademy/session.go
   [source,go]
  
positive.code: 
  [source,go]
  ----
  pool.SaleOrder().AddMany2OneField("Customer", models.ForeignKeyFieldParams{Relation: "Partner"})
  
  fmt.Println(myOrder().Customer().Name())
  ----
  
negative.code: func init() {
      pool.OpenAcademyWizard().DeclareTransientModel()
      pool.OpenAcademyWizard().AddMany2OneField("Session", models.ForeignKeyFieldParams{
          RelationModel: pool.OpenAcademySession(), Required: true})
      pool.OpenAcademyWizard().AddMany2ManyField("Attendees", models.Many2ManyFieldParams{
          RelationModel: pool.Partner()})
  }
  ----
  
  