Relations between models

Looking again at our module design, we have these relations:

• Each task has a stage – that's a many to one relation, also known as a foreign key. The inverse relation is a one to many, meaning that each stage can have many tasks.

• Each task can have many tags – that's a many to many relation. The inverse relation, of course, is also a many to many, since each tag can also have many tasks.

Let's add the corresponding relation fields to the to-do tasks in our todo_ui/todo_model.py file:

class TodoTask(models.Model):
    _inherit = 'todo.task'
    stage_id = fields.Many2one('todo.task.stage', 'Stage')
    tag_ids = fields.Many2many('todo.task.tag', string='Tags')

The preceding code shows the basic syntax for these fields, setting the related model and the field's title string. The convention for relational field names is to append _id or _ids to the field names, for to one and to many relations, respectively.

As an exercise, you may try to also add on the related models, the...