15.7. Django Models: Database Queries
In developing systems using Python and Django, one of the most essential parts is the interaction with the database. In Django, this interaction is facilitated through the use of Models and the ORM (Object-Relational Mapping) that allows to execute queries in the database, without the need to write explicit SQL.
Understanding Models in Django
Models in Django are the high-level representation of your data in the database. They are used to define the tables in the database and also to define how interaction with these tables should take place. Every model in Django is a subclass of django.db.models.Model, and each attribute of the class represents a field in the database table.
Performing Queries in the Database
In Django, the high-level database API is used to interact with the database. This API is extremely powerful and flexible, allowing you to run a wide variety of queries, from the simplest to the most complex.
To perform a database query, you use the objects attribute of the model, which is a model manager. This model manager has a number of methods that can be used to execute database queries.
Simple Queries
For example, to retrieve all records from a table, you would use the all() method. For example:
all_records = MyModel.objects.all()To retrieve a single record based on a condition, you would use the get() method. For example:
record = MyModel.objects.get(id=1)Complex Queries
For more complex queries, you can use the filter() method. This method returns a new query set, which can be filtered further or can be used to retrieve the records. For example:
records = MyModel.objects.filter(name='John')You can also chain multiple filters together. For example:
records = MyModel.objects.filter(name='John').filter(age__lt=30)The example above will return all records where the name is 'John' and the age is less than 30.
Conclusion
Working with the Django database API is an essential part of developing systems using Python and Django. It provides a high-level interface for interacting with the database, allowing you to focus on your application's logic instead of worrying about the SQL. Learning to use this API effectively is a crucial step in becoming an effective Django developer.
