Django custom validation of multiple fields - django

Question

for which I want to validate a number of fields in a custom clean method.
I have this so far:
class ProjectInfoForm(forms.Form):
module = forms.ModelChoiceField(
queryset=Module.objects.all(),
)
piece = forms.CharField(
widget=forms.Select(),
required=False,
)
span = forms.IntegerField(
max_value=100,
initial=48
)
max_span = forms.IntegerField(
max_value=100,
initial=0
)
def clean(self):
span = self.cleaned_data['span']
max_span = self.cleaned_data['max_span']
piece = self.cleaned_data.['piece']
# validate piece
try:
Piece.objects.get(pk=m)
except Piece.DoesNotExist:
raise forms.ValidationError(
'Illegal Piece selected!'
)
self._errors["piece"] = "Please enter a valid model"
# validate spans
if span > max_span:
raise forms.ValidationError(
'Span must be less than or equal to Maximum Span'
)
self._errors["span"] = "Please enter a valid span"
return self.cleaned_data
However, this only gives me one of the messages if both clauses invalidate. How can I get all the invalid messages. Also I do not get the field-specific messages - how do I include a message to be displayed for the specific field?
Any help much appreciated.

Answer 1

Store the errors and don't raise them until the end of the method:
def clean(self):
span = self.cleaned_data['span']
max_span = self.cleaned_data['max_span']
piece = self.cleaned_data.['piece']
error_messages = []
# validate piece
try:
Piece.objects.get(pk=m)
except Piece.DoesNotExist:
error_messages.append('Illegal Piece selected')
self._errors["piece"] = "Please enter a valid model"
# validate spans
if span > max_span:
error_messages.append('Span must be less than or equal to Maximum Span')
self._errors["span"] = "Please enter a valid span"
if len(error_messages):
raise forms.ValidationError(' & '.join(error_messages))
return self.cleaned_data

Answer 2

You should write a custom clean_FIELDNAME method in this case. That way, field centric validation errors can later be displayed as such when using {{form.errors}} in your template. The clean method o.t.h. is for validating logic that spans more than one field. Take a look through the link I posted above, everything you need to know about validating django forms is in there.

Answer 3

It happens because you are using raise.
Try replace it by these two line in your code:
del self.cleaned_data['piece']
and
del self.cleaned_data['span']

Answer 4

It appears this has changed in later versions of Django (this seems to work in 2.1 and later):
from django import forms
class ContactForm(forms.Form):
# Everything as before.
...
def clean(self):
cleaned_data = super().clean()
cc_myself = cleaned_data.get("cc_myself")
subject = cleaned_data.get("subject")
if cc_myself and subject and "help" not in subject:
msg = "Must put 'help' in subject when cc'ing yourself."
self.add_error('cc_myself', msg)
self.add_error('subject', msg)
https://docs.djangoproject.com/en/dev/ref/forms/validation/#raising-multiple-errors has more details.