Handling ManyToMany Relationships with Extra Fields in Django

To handle your ManyToMany relationship with extra fields through the TitleReelRecord model, you'll need to use inline formsets. Here's how to implement this for your microfilm reel inventory system:

1. Create a ModelForm for TitleReelRecord

First, create a form for the TitleReelRecord model:

PYTHONCopied
class TitleReelRecordForm(forms.ModelForm):
    class Meta:
        model = TitleReelRecord
        fields = ['title_id', 'begin_date', 'end_date', 'title_order']
        widgets = {
            'begin_date': forms.DateInput(attrs={'type': 'date'}),
            'end_date': forms.DateInput(attrs={'type': 'date'}),
        }

2. Create an Inline Formset for TitleReelRecord

Next, create an inline formset that will allow you to add multiple TitleReelRecord instances:

PYTHONCopied
from django.forms import inlineformset_factory

TitleReelRecordFormSet = inlineformset_factory(
    Reel,
    TitleReelRecord,
    form=TitleReelRecordForm,
    extra=1,  # Start with one empty form
    can_delete=True  # Allow deleting existing relationships
)

3. Modify Your ReelCreateView to Handle the Formset

Update your ReelCreateView to handle both the reel form and the title relationship formset:

PYTHONCopied
class ReelCreateView(CreateView):
    model = Reel
    form_class = AddReelForm
    template_name = 'your_app/reel_form.html'
    
    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        if self.request.POST:
            context['title_formset'] = TitleReelRecordFormSet(self.request.POST)
        else:
            context['title_formset'] = TitleReelRecordFormSet()
        return context
    
    def form_valid(self, form):
        context = self.get_context_data()
        title_formset = context['title_formset']
        
        # Set last_updated field before saving
        form.instance.last_updated = datetime.now().strftime("%Y-%m-%d %H:%M:%S")
        
        if title_formset.is_valid():
            self.object = form.save()
            title_formset.instance = self.object
            title_formset.save()
            return super().form_valid(form)
        else:
            return self.render_to_response(self.get_context_data(form=form))

4. Update the ReelUpdateView Similarly

PYTHONCopied
class ReelUpdateView(UpdateView):
    model = Reel
    form_class = AddReelForm
    template_name = 'your_app/reel_form.html'
    
    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        if self.request.POST:
            context['title_formset'] = TitleReelRecordFormSet(
                self.request.POST, instance=self.object
            )
        else:
            context['title_formset'] = TitleReelRecordFormSet(instance=self.object)
        return context
    
    def form_valid(self, form):
        context = self.get_context_data()
        title_formset = context['title_formset']
        
        # Set last_updated field before saving
        form.instance.last_updated = datetime.now().strftime("%Y-%m-%d %H:%M:%S")
        
        if title_formset.is_valid():
            self.object = form.save()
            title_formset.instance = self.object
            title_formset.save()
            return super().form_valid(form)
        else:
            return self.render_to_response(self.get_context_data(form=form))

5. Create a Template to Display Both Forms

Create a template that displays both the reel form and the title relationship formset:

HTMLCopied
{% extends "base.html" %}

{% block content %}
<h1>{% if object %}Edit{% else %}Add{% endif %} Reel</h1>

<form method="post">
    {% csrf_token %}
    
    <h2>Reel Information</h2>
    {{ form.as_p }}
    
    <h2>Associated Titles</h2>
    {{ title_formset.management_form }}
    
    <div id="title-formset">
        {% for title_form in title_formset %}
            <div class="title-form">
                {{ title_form.as_p }}
                {% if title_formset.can_delete %}
                    <p>{{ title_form.DELETE }} Delete this title association</p>
                {% endif %}
            </div>
        {% endfor %}
    </div>
    
    <button type="button" id="add-title">Add Another Title</button>
    <button type="submit">Save</button>
</form>

<script>
    // JavaScript to dynamically add more title forms
    document.getElementById('add-title').addEventListener('click', function() {
        const formsetContainer = document.getElementById('title-formset');
        const formCount = document.getElementById('id_titlereelrecord_set-TOTAL_FORMS');
        
        // Clone the first form
        const newForm = formsetContainer.querySelector('.title-form').cloneNode(true);
        
        // Update form index in IDs and names
        const newIndex = parseInt(formCount.value);
        const oldIndex = 0;  // Assuming we're cloning the first form
        
        newForm.innerHTML = newForm.innerHTML.replace(
            new RegExp('titlereelrecord_set-' + oldIndex, 'g'),
            'titlereelrecord_set-' + newIndex
        );
        
        // Clear input values in the new form
        newForm.querySelectorAll('input[type="text"], input[type="date"], select').forEach(input => {
            input.value = '';
        });
        
        // Add the new form to the container
        formsetContainer.appendChild(newForm);
        
        // Update the form count
        formCount.value = newIndex + 1;
    });
</script>
{% endblock %}

6. Handling the Last_Updated Field

For both the Reel and TitleReelRecord models, you need to set the last_updated field. You can do this in the form_valid method:

PYTHONCopied
def form_valid(self, form):
    context = self.get_context_data()
    title_formset = context['title_formset']
    
    # Set last_updated field for the Reel
    form.instance.last_updated = datetime.now().strftime("%Y-%m-%d %H:%M:%S")
    
    if title_formset.is_valid():
        self.object = form.save()
        title_formset.instance = self.object
        
        # Set last_updated field for each TitleReelRecord
        for title_form in title_formset:
            if title_form.is_valid() and not title_form.cleaned_data.get('DELETE', False):
                title_form.instance.last_updated = datetime.now().strftime("%Y-%m-%d %H:%M:%S")
        
        title_formset.save()
        return super().form_valid(form)
    else:
        return self.render_to_response(self.get_context_data(form=form))

Summary

This implementation allows you to:

1. Create a Reel with its basic information
2. Add one or more Title associations with their extra fields (begin_date, end_date, title_order)
3. Dynamically add more Title associations using JavaScript
4. Update existing Reels and their Title associations
5. Delete Title associations from a Reel

The key components are:

• A ModelForm for TitleReelRecord
• An inline formset factory
• Modified CreateView and UpdateView classes to handle both forms
• A template that displays both forms and includes JavaScript for dynamic form addition

This approach leverages Django's formsets to handle the complexity of managing many-to-many relationships with extra fields.