Adding a hierarchy to a model

Hierarchies are represented like a model having relations with the same model. Each record has a parent record in the same model, and many child records. This can be achieved by simply using many-to-one relations between the model and itself.

However, Odoo also provides improved support for this type of field by using the nested set model (https://en.wikipedia.org/wiki/Nested_set_model). When activated, queries using the child_of operator in their domain filters will run significantly faster.

Staying with the Library Books example, we will build a hierarchical category tree that can be used to categorize books.

Getting ready

We will continue using the my_library add-on module from the previous recipe.

How to do it...

We will add a new Python file, models/library_book_categ.py, for the category tree, as follows:

1. To load the new Python code file, add the following line to models/__init__.py:

   from . import library_book_categ

2. To...