Django: Advanced Models
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This document summarizes content from Chapter 10 of an advanced Django models book. It discusses related objects, making changes to database schemas by adding or removing fields and models, managers, model methods, and executing raw SQL queries. Key points include using foreign keys and many-to-many fields for related objects, running SQL alter statements to add columns, and defining custom managers and model methods to modify initial querysets and add row-level functionality.
![Adding Fields
2. Run manage.py sqlall [app] to see the new CREATE TABLE statement for the
model
Development Environment
✐column definition for the new field](https://image.slidesharecdn.com/djangogirl-151008133912-lva1-app6891/85/Django-Advanced-Models-13-320.jpg)
![Adding Fields
Development Environment
1. Add the field to your model.
2. Run manage.py sqlall [app] to see the new CREATE TABLE statement for the
model. Note the column definition for the new field.
3. Start database’s interactive shell (e.g., psql or mysql, or you can use
manage.py dbshell). Execute an ALTER TABLE statement that adds your
new column.
4. Verify with Python interactive shell manage.py shell by importing the
model and selecting from the table (e.g., MyModel.objects.all()[:5]).](https://image.slidesharecdn.com/djangogirl-151008133912-lva1-app6891/85/Django-Advanced-Models-16-320.jpg)
Django: Advanced Models
- 1. Chapter 10 Advanced Model Anne Lai Django Girls meetup 2015/10/8 Django Book
- 2. • Related Objects • Making Changes to a Database Schema • Manager • Model Methods • Executing Raw SQL Queries Outline
- 3. Recall of Chapter 5 • Define models • Use the database API to create, retrieve, update and delete records
- 5. Related Objects • ForeignKey • ManyToManyField
- 7. Related Objects ✐return QuerySet values instead of model instances
- 8. Related Objects ✐ book_set = lowercase(Book) + “_set” QuerySet
- 9. Making Changes to a Database Schema
- 10. Making Changes to a Database Schema • syncdb sync model to the database merely creates tables that don’t yet exist in database does not sync changes in models or perform deletions of models
- 11. Making Changes to a Database Schema • Adding Fields • Removing (normal/ Many-to-Many) Fields • Removing Models
- 12. Adding Fields Development Environment 1. Add the field to your model ✐a database column will contain NULL values when first created.
- 13. Adding Fields 2. Run manage.py sqlall [app] to see the new CREATE TABLE statement for the model Development Environment ✐column definition for the new field
- 14. Adding Fields 3. Start database’s interactive shell (e.g., psql or mysql, or you can use manage.py dbshell) Execute an ALTER TABLE statement that adds your new column Development Environment NULL column NOT NULL column
- 15. Adding Fields 4. Verify with Python interactive shell manage.py shell Development Environment ✐ If a model contains a field that has not yet been created in the database table, it will cause an error happens at code execution time.
- 16. Adding Fields Development Environment 1. Add the field to your model. 2. Run manage.py sqlall [app] to see the new CREATE TABLE statement for the model. Note the column definition for the new field. 3. Start database’s interactive shell (e.g., psql or mysql, or you can use manage.py dbshell). Execute an ALTER TABLE statement that adds your new column. 4. Verify with Python interactive shell manage.py shell by importing the model and selecting from the table (e.g., MyModel.objects.all()[:5]).
- 17. Adding Fields Production Server 1. Start database’s interactive shell (e.g., psql or mysql, or you can use manage.py dbshell) 2. Execute the ALTER TABLE statement 3. Add the field to your model. If you’re using source-code revision control and you checked in your change in development environment step 1, now is the time to update the code (e.g., svn update, with Subversion) on the production server 4. Restart the Web server
- 18. Removing Fields 1. Remove the field from model and restart the Web server. 2. Remove the column from your database, using a command like this: ✐ Order sensitive 1. Remove the ManyToManyField from model and restart the Web server. 2. Remove the many-to-many table from your database, using a command like this: Normal Field Many-to-Many Field
- 19. Removing Models 1. Remove the model from your models.py file and restart the Web server. 2. Remove the table from your database, using a command like this: ✐ Order sensitive
- 20. Manager
- 21. Manager • Adding Extra Manager Methods • Modifying Initial Manager QuerySets • Multiple Managers ✐ Managers = database queries
- 22. Adding Extra Manager Methods
- 23. Adding Extra Manager Methods ✐ manager itself (objects) ✐ extends django.db.models.Manager ✐ replacing the “default” manager
- 24. Modifying Initial Manager QuerySets QuerySet
- 25. Multiple Managers ✐ Django interprets the first Manager defined in a class as the “default” Manager
- 26. Model Methods
- 27. Model Methods http://www.python.org/download/releases/2.2/descrintro/#property ✐property(fget=None, fset=None, fdel=None, doc=None)
- 28. • Model Method: “row-level” functionality to objects Act on a particular model instance • Managers: “table-wide” or “table-level” Comparison
- 29. Executing Raw SQL Queries
- 30. Executing Raw SQL Queries ✐ current db connection ✐use placeholders rather than adding parameters directly within the SQL standard Python “DB-API”: https://www.python.org/dev/peps/pep-0249/
- 31. Thank you