Question

I’m creating the "Order" form for the Parts.

My AddOrderForm has Order Model fields (like quantity) but at the same time some Part-related info from Part Model (like name_in_english) and PartNumber Model (like number) and some other fields…

First I did Separate ModelForm for each one and them combined them like this:

forms.py

class PartNumberForAddOrderForm(forms.ModelForm):

    class Meta:
        model = PartNumber
        fields = ('number',)

class PartForAddOrderForm(forms.ModelForm):

    class Meta:
        model = Part
        fields = ('manufacturer','name_in_english')

class AddOrderForm(forms.ModelForm):

    class Meta:
        model = Order
        fields = ('quantity',)

in template:

<form class="form-inline well" id="add_order">
    <div class="row-fluid">
        <div class="span12">

        {% crispy form_part_number %}
        {% crispy form_part %}
        {% crispy form_order %}
        
        <input type="submit" class="btn btn-primary pull-right" value="{% trans 'Add' %}"/>
        </div>
    </div>  
</form>

With this view became:
form_part_number.is_valid() and form_part.is_valid() and form_order.is_valid():

All this looks SUPER ugly and just wrong…

So I created the other way:

class PartForm(forms.ModelForm):

    class Meta:
        model = Part
        fields = ('manufacturer','name_in_english')

class PartNumberForm(forms.ModelForm):

    class Meta:
        model = PartNumber
        fields = ('number',)

class AddOrderForm(forms.ModelForm):
    manufacturer = PartForm.base_fields['manufacturer']
    name_in_english = PartForm.base_fields['name_in_english']
    number = PartNumber.base_fields['number']

    class Meta:
        model = Order
        fields = ('manufacturer','number','quantity','name_in_english')
    

QUESTIONS: Is this Form.base_fields[''] legal way? I assume the .save() will not work, but .is_valid() should be fine, right? Is there any better way to do it?

I could fine anything helpful anywhere so this is something I came up with myself. and that worries me.

Thanks

Answer 1

The is_valid() call will probably validate the individual fields correctly, but it might ignore other model validation, for example a unique_together statement or a custom clean method on one of the other models.

I don’t think that checking is_valid() for multiple forms is that ugly. I’ve used it before, and immediately understand what you’re doing. However, I’ve never seen anyone define a form by grabbing a fields from another forms base_fields before. That doesn’t mean it won’t work, but it is unconventional.

If you’re really concerned about it being ugly, you could do something like the following:

my_forms = [form_part_number, form_part, form_order]
if all(f.is_valid() for f in my_forms):
    ...