Introduction to model mixins¶

Lino comes with a collection of mixin classes for database models that encapsulate higher-level application concepts.

A model mixin is a class meant to mixed into the list of parent classes when defining a database model. For example lino.mixins.Contactable means “somebody who can be contacted by email in a given language”. Here is how to use this model mixin:

class ContactPerson(dd.Model, Contactable):
    ...

The above ContactPerson model will “automatically” have two fields email and language. These fields are defined on the lino.mixins.Contactable mixin.

Here is a list of some model mixins that that are worth to know:

lino.mixins.Contactable : somebody who can be contacted by email in a given language
lino.modlib.printing.Printable : something that can be printed
lino.mixins.CreatedModified : adds two read-only timestamp fields created and modified
lino.mixins.periods.DateRange : adds two fields start_date and end_date.
lino.modlib.users.UserAuthored : adds a field user, which is automatically set to the user who created a row.
lino.mixins.sequenced.Sequenced: adds a field seqno, and integer that holds the sequence number of this row among its siblings.
lino.modlib.gfks.Controllable: adds a field owner, a generic foreign key to some other database row that is considered as its “owner” or “controller”. The exact verbose name for the owner is configurable by the application developer.

That should be enough for an introduction, but I can tell you already now that Lino has many mixins. Some more examples:

lino.modlib.comments.Commentable
lino.utils.mldbc.mixins.BabelNamed
lino.utils.mldbc.mixins.BabelDesignated
lino.modlib.users.PrivacyRelevant
lino.modlib.users.Assignable
lino.mixins.sequenced.Hierarchical
lino.modlib.uploads.UploadController
lino.mixins.ref.Referrable
lino.modlib.memo.MemoReferrable
lino.modlib.publisher.Illustrated
lino.modlib.publisher.Publishable
lino.mixins.periods.DateRangeObservable

See also lino.core.model and lino.mixins.