#28346: Misleading error message when validator cannot be serialized
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Reporter: Peter Inglesby | Owner: nobody
Type: Uncategorized | Status: new
Component: Migrations | Version: 1.11
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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I have a validator factory that looks like this:
{{{
def validate_max_words(max_words):
def validator(value):
num_words = len(value.split())
if num_words > max_words:
raise ValidationError(f'Field is too long: {num_words} words /
{max_words} limit')
return validator
}}}
and I would like to use it in a field definition like this:
{{{
description = models.TextField(validators=[validate_max_words(300)])
}}}
However, when running a migration to create the model in question, I get
the following error:
{{{
ValueError: Could not find function validator in myapp.validators.
Please note that due to Python 2 limitations, you cannot serialize unbound
method functions (e.g. a method declared and used in the same class body).
Please move the function into the main module body to use migrations.
For more information, see
https://docs.djangoproject.com/en/1.11/topics/migrations/#serializing-
values
}}}
The error message is misleading, in that it assumes that because the
validator cannot be serialized, it must be an unbound method. However,
this is not the case -- the validator is instead a function that's
returned by another function.
--
Ticket URL: <https://code.djangoproject.com/ticket/28346>
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