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Various programming stuff

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Django authority data

Introduction

One common requirement in an organization is to separate users in authorities (meaning departments / units / branches etc) and each authority have its own data. So users belonging to the “Athens Branch” won’t be able to edit data submitted from users of the “Thessaloniki Branch”.

This is a special case of the more general row-level-security in which each instance of a domain object will have an ACL. Row-level-security would need a many-to-many relation between object instances and authorities, something that would be overkill in our case.

Authority data is also a more general case of the user-data meaning that each user can have access to data that he inserts in the system. Implementing user-data is easy using the techniques we will present below.

We have to notice that the django permissions do not support our requirements since they define security for all instances of a model.

Defining authorities

In order to have custom authorities I propose first of all to add an Authority model that would define the authority. Even if your authorities only have a name I believe that adding the Authority model would be beneficial. Now, there are many ways to separate normal django users (django.contrib.auth.models.User) to authorities:

Using groups

Just define a django.contrib.auth.models.Group for each authority and add the users to the groups you want using the django-admin. Your Authority model would have an one-to-one relation with the django.contrib.auth.models.Group so you will be able to find out the other information of the authority (since django groups only have names).

Now you can just get the groups for the user and find out his authorities. This could lead to problems when users belong to django groups that are not related to authorities so you must filter these out (for instance by checking which groups actually have a corresponding Authority).

By storing the authority to the session

When the user logs in you can add an attribute to the session that would save the authority of the user. To do that, you should define a custom middleware that checks to see if there is an authority attribute to the session and if not it will do whatever it needs to find it and set it. An example is this:

class CustomAuthorityMiddleware:
  def process_request(self, request):
    if not request.session.get('authority'):
      authority = get_the_authority(request.user)
      request.session['authority']=authority

This way, whenever you want to find out the authority of the user you just check the session.

By using a Custom User Profile

Just create a django user profile and add to it a ForeignKey to your Authority model:

class Profile(models.Model):
  user = models.OneToOneField('django.auth.User')
  authority = models.ForeignKey('authorities.Authority', blank=True, null=True )

class Authority(models.Model):
  id = models.IntegerField(primary_key = True)
  name = models.CharField(max_length=64, )
  auth_type = models.CharField(max_length=16, )

You can get the authority of the user through request.user.profile.authority.

Getting the authority of the user has to be DRY

Whatever method you use to define the authorities of your users you have to remember that it is very important to define somewhere a function that will return the authority (or authorities) of a user. You need to define a function even in the simple case in which your function would just return request.user.profile.authority. This will greatly help you when you wish to add some logic to this, for instance “quickly disable users belonging to Authority X or temporary move users from Authority Y to authority Z”.

Let us suppose that you have defined a get_user_authority function. Also, you need to define a has_access function that would decide if a users/request has access to a particular object. This also needs to be DRY.

Adding authority data

To define authority data you have to add a field to your model that would define its authority, for instance like this:

class AuthorityData(models.Model):
  authority = models.ForeignKey('authorities.Authority', editable=False,)

This field should not be editable (at least by your end users) because they shouldn’t be able to change the authority of the data they insert.

If you want to have user-data then just add a models.ForeignKey('django.auth.User', editable=False)

Now, your Create and Update Class Based Views have to pass the request to your forms and also your Detail and Update CBV should allow only getting objects that belong to the authority of the user:

class AuthorityDataCreateView(CreateView):
  model=models.AuthorityData

  def get_form_kwargs(self):
      kwargs = super(AuthorityDataCreateView, self).get_form_kwargs()
      kwargs.update({'request': self.request})
      return kwargs

class AuthorityDataDetailView(DetailView):
  def get_object(self, queryset=None):
      obj = super(AuthorityDataDetailView, self).get_object(queryset)
      if if not user_has_access(obj, self.request):
          raise Http404(u"Access Denied")
      return obj

class AuthorityDataUpdateView(UpdateView):
  model=models.AuthorityData

  def get_form_kwargs(self):
      kwargs = super(AuthorityDataUpdateView, self).get_form_kwargs()
      kwargs.update({'request': self.request})
      return kwargs

  def get_object(self, queryset=None):
      obj = super(AuthorityDataUpdateView, self).get_object(queryset)
      if if not user_has_access(obj, self.request):
          raise Http404(u"Access Denied")
      return obj

Your ModelForm can now use the request to get the Authority and set it (don’t forget that you should not use Meta.exclude but instead use Meta.include!):

class AuthorityDataModelForm(forms.ModelForm):
    class Meta:
      model = models.AuthorityData
      exclude = ('authority',)

    def __init__(self, *args, **kwargs):
      self.request = kwargs.pop('request', None)
      super(ActionModelForm, self).__init__(*args, **kwargs)


    def save(self, force_insert=False, force_update=False, commit=True):
      obj = super(AuthorityDataModelForm, self).save(commit=False)
      if obj:
          obj.authority = get_user_authority(self.request)
          obj.save()
      return obj

The previous work fine for Create/Detail/Update CBVs but not for ListsViews. List views querysets and in general all queries to the object have to be filtered through authority.

class AuthorityDataListView(ListView):
  def get_queryset(self):
    queryset = super(AuthorityDataModelForm, self).get_queryset()
    return queryset.filter(authority = get_user_authority(request))

Conclusion

Using the above techniques we can define authority (or just user) data. Your AuthorityData should have a ForeignKey to your Authority and you have configure your queries, ModelForms and CBVs to use that. If you have more than one models that belong to an authority and want to stay DRY then you’d need to define all the above as mixins.

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