How to validate contents of a CSV file using Django forms - django

Question

I have a web app that needs to do the following:
Present a form to request a client side file for CSV import.
Validate the data in the CSV file or ask for another filename.
At one point, I was doing the CSV data validation in the view, after the form.is_valid() call from getting the filename (i.e. I have the imported CSV file into memory in a dictionary using csv.DictReader). After running into problems trying to pass errors back to the original form, I'm now trying to validate the CONTENTS of the CSV file in the form's clean() method.
I'm currently stumped on how to access the in memory file from clean() as the request.FILES object isn't valid. Note that I have no problems presenting the form to the client browser and then manipulating the resulting CSV file. The real issue is how to validate the contents of the CSV file - if I assume the data format is correct I can import it to my models. I'll post my forms.py file to show where I currently am after moving the code from the view to the form:
forms.py
import csv
from django import forms
from io import TextIOWrapper
class CSVImportForm(forms.Form):
filename = forms.FileField(label='Select a CSV file to import:',)
def clean(self):
cleaned_data = super(CSVImportForm, self).clean()
f = TextIOWrapper(request.FILES['filename'].file, encoding='ASCII')
result_csvlist = csv.DictReader(f)
# first line (only) contains additional information about the event
# let's validate that against its form definition
event_info = next(result_csvlist)
f_eventinfo = ResultsForm(event_info)
if not f_eventinfo.is_valid():
raise forms.ValidationError("Error validating 1st line of data (after header) in CSV")
return cleaned_data
class ResultsForm(forms.Form):
RESULT_CHOICES = (('Won', 'Won'),
('Lost', 'Lost'),
('Tie', 'Tie'),
('WonByForfeit', 'WonByForfeit'),
('LostByForfeit', 'LostByForfeit'))
Team1 = forms.CharField(min_length=10, max_length=11)
Team2 = forms.CharField(min_length=10, max_length=11)
Result = forms.ChoiceField(choices=RESULT_CHOICES)
Score = forms.CharField()
Event = forms.CharField()
Venue = forms.CharField()
Date = forms.DateField()
Div = forms.CharField()
Website = forms.URLField(required=False)
TD = forms.CharField(required=False)
I'd love input on what's the "best" method to validate the contents of an uploaded CSV file and present that information back to the client browser!

Answer 1

I assume that when you want to access that file is in this line inside the clean method:
f = TextIOWrapper(request.FILES['filename'].file, encoding='ASCII')
You can't use that line because request doesn't exist but you can access your form's fields so you can try this instead:
f = TextIOWrapper(self.cleaned_data.get('filename'), encoding='ASCII')
Since you have done super.clean in the first line in your method, that should work. Then, if you want to add custom error message to you form you can do it like this:
from django.forms.util import ErrorList
errors = form._errors.setdefault("filename", ErrorList())
errors.append(u"CSV file incorrect")
Hope it helps.