A help in concept and a database query question (Django/Python)

Question

I am trying to build a kind of news website for learning purposes.

class NewsCategory(models.Model):
    category = models.CharField(max_length=50)

Note: A category can be Soccer, Tennis, business ... User can register to different news category. This choice will be saved in their preferences.

class Profile(models.Model):
    user = models.ForeignKey(User, unique=True)
    gender = models.CharField(max_length=1,blank=True)
    preference = models.ManyToManyField(NewsCategory)

I am currently stuck on how to update the preference list of each user (the list that specifies in which categories he is interested in.)

View:

category = [(item.category) for item in NewsCategory.objects.all()]

and then I am sending the category to the template below

template:

<div id="c_b">
    {% for c in category %}
        <input type="checkbox" name="category[]" value="{{c}}">
        <label for="{{c}}">{{c}}</label>
    {% endfor %}
</div>

Questions:

1. What is the best way to add the checked tag next to the checkboxes that are already saved in the user's preference when I display the template.

   I though of getting all the preferences users are registered for: saved_preference = user.preference.all() and then checking for each item in category if it is in saved_preference

   I am also blanking out on the way to actually write that into code, and whether this should be done in the view or the template.

2. What is a good way to update the user preference list?

   I was planning on running user.preference.clear() and then going through every item in the submitted form and running user.preference.add(the_new_preference)

Answer 1

You'll need to pass the complete list of categories and also an index of user-selected categories to your template. You don't need to convert the NewsCategory queryset into a list in your view, by the way:

View

categories = NewsCategory.objects.all()
user_preferences = [item.id for item in Profile.preference.all()]

The user_preferences variable will act as a lookup index for our template.

Then you loop through all the categories in the template, and check to see if it exists in the list of user preferences:

Template

<div id="c_b">
{% for c in categories %}
    <input type="checkbox" name="category[]" id="id_{{ c.category }}" value="{{ c.id }}" {% if c.id in user_preferences %}checked="checked"{% endif %} />
    <label for="id_{{ c.id }}">{{ c.category }}</label>
{% endfor %}
</div>

Update - saving user preferences

There is no hard and fast rule here. The main consideration, as far as I am concerned, would be minimising database hits. You can just clear the user preferences, like you say, and add the new ones - in fact, this is how Django's admin handles it. Just make use of Django's transaction management:

from django.db import transaction

@transaction.commit_manually
def add_preferences(user, preferences):
  user.preference.clear()
  for pref in preferences:
    user.preference.add(pref)
  transaction.commit()

Answer 2

You should learn about forms and model forms in django. It would be the best way for both adding and changing. Forms will do the most of job for you.