Learning foreign keys¶
The application developer can turn any foreign key field into a learning foreign key.
- learning foreign key
A foreign key that can "learn", i.e. add new items to its list of choices.
- learning chooser
The chooser associated to a learning foreign key.
Usage¶
Define a chooser for the field by defining a
FOO_choices()method on the model and decorating it with@dd.chooser.Define an instance
create_FOO_choicemethod on the model.
You can disable a learning foreign key by setting the
lino.core.model.Model.disable_create_choice model attribute to True.
Examples¶
The city field of a postal
address. When you specify the name of a city that does not yet exist, you simply
leave the "invalid" city name in the combobox (Lino accepts it) and save the
partner. Lino will then silently create a city of that name. Note that you must
at least set the country, otherwise Lino refuses to automatically create
a city. This behaviour is defined in the countries.CountryCity model mixin, which is inherited e.g. by
contacts.Partner. or
addresses.Address
Or the lino_xl.lib.contacts.Role.person field. You can see the new
feature in every application with contacts. For example
lino_book.projects.min1. In the detail of a company, you have the
RolesByCompany slave table. In
the Person column of that table you can type the name of a person that does
not yet exist in the database. Lino will create it silently, and you can then
click on the pointer to edit more information.
Some examples in Automatically creating contact persons.
Implementation details¶
When a method is decorated with the chooser decorator, Lino creates a
lino.utils.choosers.Chooser instance. The can_create_choice attribute of this instance will
automatically be set to True when the field's model also has a method named
create_FOO_choice
(FOO being the field name).