Django (Model)Form Field: Manytomany with key value pair - django

Question

I have a situation where I need to do something similar to rendering a formset within a formset. But I'd rather focus on the problem before jumping to a solution.
In English first:
I'm creating a shipment from a warehouse.
Each shipment can contain multiple lines (unique combinations of product_type and package_type) with an item_count
However for each line there could be multiple "Packages" - a package_type of a product_type that has an item_count. Think of this as a batch.
The customer is only interested in seeing one line for each product_type/package_type
But we need to pull out the stock and correctly attribute the particular units from each batch to allow stock control, recall control etc to function. Therefore the dispatch staff IS interested in exactly which Packages are shipped.
Add to this the sales staff enter a SalesOrder that only specifies the product_type/package_type. They aren't interested in the Packages either. (Think putting in a forward order for next month - who knows what will be in stock then?).
Now the models (simplified for clarity):
class Package(models.Model):
create_date = models.DateField()
quantity = models.FloatField()
package_type = models.ForeignKey(PackageType, on_delete=models.PROTECT)
product_type = models.ForeignKey(ProductType, on_delete=models.PROTECT)
class CheckOut(models.Model):
package = models.ForeignKey(Package, on_delete=models.PROTECT)
create_date = models.DateField()
quantity = models.FloatField()
class Shipment(models.Model):
sales_order = models.ForeignKey(SalesOrder, null=True, blank=True)
ship_date = models.DateField(default=date.today,
verbose_name='Ship Date')
class ShipmentLine(models.Model):
shipment = models.ForeignKey(Shipment, null=True, blank=True)
sales_order_line = models.ForeignKey(SalesOrderLine, null=True, blank=True)
quantity = models.FloatField(verbose_name='Quantity Shipped')
checkout = models.ManytoManyField(CheckOut)
I currently have it working well with the constraint of a 1:M relationship of CheckOut:ShipmentLine. However when changing this to a M:M, things get knarly form-wise.
In the 1:M version the Shipment form (plus formset for the ShipmentLines) looks like this:
class CreateShipmentForm(forms.ModelForm):
class Meta:
model = om.Shipment
contact = forms.ModelChoiceField(
queryset=om.Contact.objects.filter(is_customer=True, active=True),
label='Customer')
customer_ref = forms.CharField(required=False, label='Customer Reference')
sales_order = forms.ModelChoiceField(queryset=om.SalesOrder.objects.all(),
required=False, widget=forms.HiddenInput())
number = forms.CharField(label='Shipment Number', required=False,
widget=forms.TextInput(attrs={'readonly': 'readonly'}))
class CreateShipmentLineForm(forms.ModelForm):
class Meta:
model = om.ShipmentLine
widgets = {
'checkout': forms.HiddenInput()
}
fields = ('package', 'quantity', 'id',
'sales_order_line', 'checkout')
id = forms.IntegerField(widget=forms.HiddenInput())
sales_order_line = forms.ModelChoiceField(
widget=forms.HiddenInput(), required=False,
queryset=om.SalesOrderLine.objects.all())
package = forms.ModelChoiceField(required=True, queryset=None) # queryset populated in __init__, removed for brevity
So for the 1:M, I could select a package, set the quantity and done.
For M:M, I will need to select product_type, package_type, and then 1 or more packages, AND for each package a quantity. (I'll be using JS in the form to filter these)
In my mind's eye I have a few possibilities:
create a (child) formset for the Packages and quantities and include in each line of the (parent) formset
create some sort of multi-field, multi-value matrix custom form field and use that
construct a modal dialog where the M:M stuff happens and somehow save the result to the form where validation, saving happens.
I hope I have explained it correctly and clearly enough. It's the most complex application of Django forms I've encountered and I'm not sure what the limitations/pros/cons of each of my options is.
Has anyone encountered this situation and have a solution? Or any words to the wise?
My thanks in advance,
Nathan

Answer 1

I have a similar situation, I am doing something like your second and third options:
I have overridden __init__() and, after calling super, I have a loop that adds a value selector for every field (of course you could use a single custom element here)
Then override save() and after calling super I process the extra field adding all the values.