Our first step was to create a Python file where our new module was created.

Odoo models are objects derived from the Odoo Model Python class.

When a new model is defined, it is also added to a central model registry. This makes it easier for other modules to make modifications to it later.

Models have a few generic attributes prefixed with an underscore. The most important one is _name, providing a unique internal identifier to be used throughout the Odoo instance.

The model fields are defined as class attributes. We began defining the name field of the Char type. It is convenient for models to have this field, because by default, it is used as the record description when referenced from other models.

We also used an example of a relational field, author_ids. It defines a many-to-many relation between Library Books and the partners. A book can have many authors and each author can have written many books.

There's much more to say about models, and they will be covered in depth in Chapter 5, Application Models.

Next, we must make our module aware of this new Python file. This is done by the __init__.py files. Since we placed the code inside the models/ subdirectory, we need the previous __init__ file to import that directory, which should in turn contain another __init__ file importing each of the code files there (just one, in our case).

Changes to Odoo models are activated by upgrading the module. The Odoo server will handle the translation of the model class into database structure changes.

Although no example is provided here, business logic can also be added to these Python files, either by adding new methods to the Model's class, or by extending the existing methods, such as create() or write(). This is addressed in Chapter 6, Basic Server-Side Development.