Auxiliary models

As discussed earlier, the 4 core models in this diagram:

ptree provides you with a fifth type of model, AuxiliaryModel, that you can use to store data that doesn’t fit well on any of the above models.

Reasons for using an auxiliary model include:

• You want a model that can be reused in any app,

like a standard questionnaire or qualification test. - Your match or participant needs to store the same type of information multiple times. For example, in a 2-participant match where Participant 1 makes an offer and Participant 2 responds, and there are multiple rounds of this process, your fields may look like this:

class Match(...):

    offer_1 = models.IntegerField()
    response_1 = models.BooleanField()

    offer_2 = models.IntegerField()
    response_2 = models.BooleanField()

    offer_3 = models.IntegerField()
    response_3 = models.BooleanField()

    ...

This is a sign that you could make your code more concise and robust with an auxiliary model. In models.py, add this:

class Round(ptree.models.AuxiliaryModel):
    offer = models.IntegerField()
    response = models.BooleanField()

In forms.py, add this:

class OfferForm(ptree.forms.ModelForm):

class Meta:

model = myapp.models.Round fields = [‘offer’]

class ResponseForm(ptree.forms.ModelForm):

class Meta:

model = myapp.models.Round fields = [‘response’]

In views.py, create a view. In this case, OfferView should inherit form ptree.views.CreateView, rather than ptree.views.UpdateView, since we are creating a Round object from scratch, rather than updating an existing Round. After a valid form submission, a new Round object will be created. and associated by a ForeignKey to the Participant who created it (as well as the current Match):

class OfferView(ViewInThisApp, ptree.views.CreateView):

    template_name = 'myapp/Offer.html'
    form_class = myapp.forms.OfferForm

Then, for Participant 2, you can retrieve the Round in an UpdateView by adding a get_object method:

class ResponseView(ViewInThisApp, ptree.views.UpdateView):

    template_name = 'myapp/Response.html'
    form_class = myapp.forms.ResponseForm

    def get_object(self):
        return OfferAndResponse.objects.get(match=self.match)

Now you can put OfferView and ResponseView into your treatment’s sequence() method multiple times in a row, to create multiple Round objects in your database.