How can triggers be used in a workflow?

Eduardo BP

Hi Odoo developers.

I have been reading the official documentation about workflows in Odoo 8, and specifically I don't understand how can I use triggers in workflows.

The documentation says:

Triggers are recorded in database as record IDs (together with the model name) and refer to the workflow instance waiting for those records. The transition definition provides a model name (attribute trigger_model) and a Python expression (attribute trigger_expression) that evaluates to a list of record IDs in the given model. Any of those records can wake up the workflow instance they are associated with.

How can I define a trigger in a transition?.

How can I activate a transition using a trigger?.

Any example, please.

Thanks a lot.