Django: Generic List and Detail Views

From learn.firstdraft and MDN Django Generic Views

Overview

• Use generic class-based list views for listing multiple records, and detail views for displaying individual records.
• Extract information from URL patterns and pass it to the view.
• These views reduce the amount of view code needed, streamlining the development process.
• Implement pagination in list views to efficiently handle large datasets.
• Apply these concepts to create pages to view our books and authors, passing data from URLs to the views.

Book List Page

• Extend the base template base_generic.html.
• Display a list of all available book records.
• URL: catalog/books/.
• Each book's title is a hyperlink to the associated book detail page.
• Display the author for each book record.

URL Mapping

Set the path for books/ in /catalog/urls.py.

The path() function:

• Defines a pattern to match the /catalog/books/ URL.
• Calls the view function returned by views.BookListView.as_view() if the URL matches.
• Provides a name for this particular URL mapping.

The view function:

• Is implemented as a class, BookListView.
• Inherits from Django's generic class-based views.
• Is converted to a view function using the as_view() method.

View (class-based)

Instead of writing the book list view as a regular function-based view (similar to a Rails controller action):

• Queries the database for all books.
• Calls render() to pass the list to a specified template.

Using a class-based generic list view (ListView) is preferable:

• Inherits from an existing view.
• The generic view already implements most of the functionality.
• Aligns with Django best practices for a more robust list view with less code, repetition, and maintenance.

In catalog/views.py, the generic view:

• Queries the database.
• Renders a template.

The template can access the list of books using a template variable. By default, generic views look for templates in the /application_name/templates/application_name/the_model_name_list.html path.

To modify the default behavior:

• Specify a different template file if you need to use multiple views for the same model.
• Use a different template variable name if needed.
• Customize the queryset to filter or change the subset of results returned.

Overriding methods in class-based views

• It is possible to override some of the class methods, offering more flexibility than just setting the queryset attribute.
• For instance, override get_context_data() to pass additional context variables to the template.

Follow this pattern:

• Get the existing context from the superclass.
• Add new context information.
• Return the new context.

See Built-in class-based generic views Django docs.

Creating the List View Template

The generic class-based list view for a Book model in a catalog application expects the template file to be located at /django-locallibrary-tutorial/catalog/templates/catalog/book_list.html. This template should extend the base template.

Conditional execution

Template tags check whether book_list has been defined and is not empty.

For more information about conditional operators, see: Django Docs.

For loops

The template uses template tags to loop and populate the book template variable.

Accessing variables

• Access the fields using dot notation: book.field_name.

Call functions in the model from within template

• Book.get_absolute_url() gets a URL to display the associated detail record.
• Note: There is no way to pass arguments.
• Warning: Be aware of side effects when calling functions in templates. Be sure not to accidentally do something destructive.

Update the Base Template

To enable the link on all pages, update /django-locallibrary-tutorial/catalog/templates/base_generic.html to use {% url 'books' %}. The URL mapping for the book detail pages is needed to create hyperlinks to individual books.

Book detail page

The book detail page displays information accessed using the URL catalog/book/<id>.

URL Mapping

In /catalog/urls.py, the 'book-detail' path function defines a URL pattern, associates it with a generic class-based detail view, and assigns it a name. The <int:pk> part captures the book ID, where pk stands for primary key, uniquely identifying the book in the database.

Passing additional options in your URL maps

You may pass a dictionary containing additional options to the view.

View (class-based)

In catalog/views.py:

class BookDetailView(generic.DetailView):
    model = Book

• Create the template at /django-locallibrary-tutorial/catalog/templates/catalog/book_detail.html
• The view will pass the Book record's information to the template.
• Access the book's details in the template using the variable named object or book (the model's name).

If the record doesn't exist ...

• Generic class-based detail view raises an exception
• Http404
• Resource not found
• This behavior can be customized

Creating the Detail View Template

For a Book model in an catalog application, the generic class-based detail view expects the template file to be located at /django-locallibrary-tutorial/catalog/templates/catalog/book_detail.html.

To create this template:

• The url template tag can reverse the 'author-detail' URL and pass it the author instance for the book. Using get_absolute_url() is preferred because any necessary changes need to be made only in the author model.

The template should:

• Extend the base template
• Override the content block.
• Use conditional processing and for loops to iterate through lists of objects.
• Access the context fields using dot notation.

Retrieve the set of BookInstance records associated with a particular Book, with the book.bookinstance_set.all() function.

Django constructs the function

• by lower-casing the ForeignKey model
• followed by _set
• Use all() to get all records

You cannot use the filter() method directly in templates because you cannot specify arguments to functions.

If you don't define an order (on your class-based view or model), there will be errors:

[date-time] "GET /catalog/books/?page=1 HTTP/1.1" 200 1637
/foo/local_library/venv/lib/python3.5/site-packages/django/views/generic/list.py:99: UnorderedObjectListWarning: Pagination may yield inconsistent results with an unordered object_list: <QuerySet [<Author: Lubiner, Samuel>, <Author: Van Rossum, Guido>, <Author: Torvalds, Linus>]>
  allow_empty_first_page=allow_empty_first_page, **kwargs)

The paginator object expects an ORDER BY clause executed on your underlying database.

Pagination

• Django has built-in support for pagination
• Incorporated into the generic class-based list views

Templates

With paginated data, add support to the template to scroll through the results set. To paginate all list views, add this to the base template. The page_obj gets all the information about the current page, previous pages, page numbers, etc.

{{ request.path }} gets the current page URL for creating the pagination links, independent of the object that we're paginating.

Book List Page

Create the author detail and list views.

Author list: catalog/authors/
Detail view for the author with a primary key field: catalog/author/<id>

• After creating the URL mapper for the author list page, update the "All authors" link in the base template.
• After creating the URL mapper for the author detail page, update the book detail view template so the author link points to the new author detail page.
• Call get_absolute_url() on the author model.

See also

• Built-in class-based generic views
• Generic display views
• Introduction to class-based views
• Built-in template tags and filters
• Pagination
• Making queries > Related objects