Max_length in Django CharFields

Question

The Django docs indicate that:

The max_length is enforced at the database level and in Django’s validation.

What, exactly does this mean? I have a routine to parse an input CSV file to create some models, and an over-length Name field got in there along the way as I created objects using:

new_standard = Standard.objects.create(Name=lname,ShortName=sname,calcmethod=method,Description=descr,course=course,Order=stdnum) new_standard.save()

The error was only raised later, as the user tried to edit the object using a form (which wouldn't validate). When using the same form to create objects, the input field won't allow typing past the 30th character, but my manual method seems to allow the over-length field to be created.

How do I avoid this (apart from manually truncating strings after checking field lengths, which I could do, but which seems like a lot of hassle - seems like I could handle it in the form or DB)? Now that I have some of these time bombs in my DB, what's the easiest way to get rid of them?

Alasdair · Accepted Answer · 2017-12-20 17:07:26Z

For historic reasons, Django validation is not called when you create or save an object, but it is triggered by model forms, including in the Django admin.

You could manually trigger validation by calling full_clean()

from django.core.exceptions import ValidationError new_standard = Standard(Name=lname,ShortName=sname,calcmethod=method,Description=descr,course=course,Order=stdnum) try: new_standard.full_clean() except ValidationError as exp: # Do something here pass else: save()

Note that max_length is not enforced by SQLite. If you were using a different database, you would get an integrity error when you tried to save a string that was too long.

I'd still have to write the code to truncate those fields, though, right? Thanks for the info on different DB behaviors, too.

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