Set default values

Default values are useful to save time for users when entering data. On Tryton default values are computed on server side and they will be set by the client when creating a new record if the field is shown on the view. If the field is not shown on the view, the server will set this values when storing the new records in the database.

In order to define a default value for a field you should define a class method named default_<field_name> that returns the default value. For example to add today as the default date of our Opportunity model the following class method is added in opportunity.py file:

from trytond.pool import Pool
...
class Opportunity(ModelSQL, ModelView):
    ...
    @classmethod
    def default_start_date(cls):
        pool = Pool()
        Date = pool.get('ir.date')
        return Date.today()

Call other model methods

In the previous example we called the today method of the Date model from the Pool instance. The __name__ value is used to get the class. It is very important to get the class from the pool instead of using a normal Python import, because the pool ensures that all of the extensions are applied depending on the activated modules. For example, if we have the company module also activated the correct timezone for the user company will be used for computing the today value.

Great, you have learned how to define default values, and how to call methods defined on other classes in the pool. Let’s continue with reacting on user input.