tasks_module4.md

Add Tag model

We want to be able to add tags to each post in order to organize them better by topic. To do that we'll create a new Tag model. Create the Tag model by adding a new class into mainapp/models.py. Name the class Tag and make it extend models.Model. In the class body, add a field called name and set it to models.CharField(). Pass it a max_length of 50.

class Tag(models.Model):
    name = models.CharField(max_length=50, unique=True)

Add method to sanitize tag input

We want all of the tags to be lowercase. To the Tag class, add a class method named clean that will set self.name to a lowercase version of itself.

    def clean(self):
        self.name = self.name.lower()

Add a string method to make Tag objects readable

To the Tag class, add a __str__ method that returns self.name.

    def __str__(self):
        return self.name

Add many to many relationship to BlogPost model for Tags

Since we want tags to categorize posts by topic, we want to create a relationship between the Tag model and the BlogPost model. In the BlogPost class, add tags as a field and set it equal to calling models.ManyToManyField() with 'Tag' and related_name='posts' as arguments.

    tags = models.ManyToManyField('Tag', related_name='posts')

Add view to show all posts with a given tag

We would like to display a Tag page that displays all of the posts with that Tag. In order to do that, we need to create a view that will generate that page. In mainapp/views.py, create a function tag_posts(request, name). In that method, simply return render(request, 'mainapp/filtered_post_list.html').

def tag_posts(request, name):
    return render(request, 'mainapp/filtered_post_list.html')

Pass title to template

Continuing in the tag_posts method, we want to pass a title for the Tag page to the template. Before the return line, clean the incoming name parameter by setting it equal to a lowercase version of itself (e.g. name.lower() ). Then, also before the return, create a title variable and set it equal to "Posts about {}".format(name). To pass the title to the template, add a dictionary as another argument to the end of the render() call. In the dictionary, set 'title' to the new title variable.

def tag_posts(request, name):
    name = name.lower()
    title = "Posts about {}".format(name)

    return render(request, 'mainapp/filtered_post_list.html', {'title':title})

Find posts and pass to template

Since we want to display all of the posts with the name tag, let's first find the Tag object. Right after the title line, call get_object_or_404(Tag, name=name) and set that equal to a variable named tag. Then, get all of the posts with that tag by calling BlogPost.objects.filter(tags=tag) and setting the result equal to a variable named posts. Finally, pass the posts list to the template by adding 'posts':posts to the dict in the render() call, {'posts':posts, 'title':title}.

def tag_posts(request, name):
    name = name.lower()
    title = "Posts about {}".format(name)
    
    tag = get_object_or_404(Tag, name=name)
    posts = BlogPost.objects.filter(tags=tag)

    return render(request, 'mainapp/filtered_post_list.html', {'posts':posts, 'title':title})

Add tag path and new view to routes

In mainapp/urls.py add a new path entry into the urlpatterns list. Pass 'tag/<str:name>' as the URL, 'views.tag_posts' as the view, and set name to 'tag_posts'.

    path('tag/<str:name>', views.tag_posts, name='tag_posts'),

Add url reverser to Tag model

To generate a url for the specified tag page, we can use django.urls reverse() function to generate the url from the view. Back in the Tag class, in mainapp/models.py, create a method get_absolute_url(self) that returns reverse('tag_posts', args=[str(self.name)]). Where tag_posts is the name of the URL we just named.

    def get_absolute_url(self):
        return reverse('tag_posts', args=[str(self.name)])

Uncomment tag section of index and post templates

Remove {% comment %} and {% endcomment %} tags from both mainapp/templates/mainapp/snippet_post_list.html and mainapp/templates/mainapp/post.html.

Add tags to the admin site

Register tags on the admin site by first importing Tag from .models in mainapp/admin.py. Then call admin.site.register on the Tag model.

from .models import BlogPost, Tag
admin.site.register(Tag)

Make migrations and migrate

Now that we’ve added our last model, Tag, we're ready for our final migration. From the command line, inside the root of the project, run the following commands:

python manage.py makemigrations
python manage.my migrate

Once created, add the newly created migrations from mainapp/migrations/ to the git repo and commit them.

Note: Make sure your venv is activated with source venv/bin/activate.