Object Relational Mapper (ORM)

An Object-Relational Mapper (ORM) is a layer of abstraction for data stored in a database with tables, rows, and columns. It lets us work with databases using familiar object-oriented metaphors which work well with code. Classes map to database tables, attributes map to columns, and an individual instance of the class represents a row of data in the database.

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In Django, the ORM’s job is to model the database, but there’s a second system that’s in charge of actually building the database called migrations. Its job is to give you the ability to add and remove tables and columns, based on changes you make to your models.py files.

One way to think of it is as a version control system for your database. As we’ll see later, it comes in particularly useful when we need to upgrade a database that’s deployed on a live server.

source: Percival