Change text_factory in Django/sqlite

Question

I have a django project that uses a sqlite database that can be written to by an external tool. The text is supposed to be UTF-8, but in some cases there will be errors in the encoding. The text is from an external source, so I cannot control the encoding. Yes, I know that I could write a "wrapping layer" between the external source and the database, but I prefer not having to do this, especially since the database already contains a lot of "bad" data.

The solution in sqlite is to change the text_factory to something like: lambda x: unicode(x, "utf-8", "ignore")

However, I don't know how to tell the Django model driver this.

The exception I get is:

'Could not decode to UTF-8 column 'Text' with text' in /var/lib/python-support/python2.5/django/db/backends/sqlite3/base.py in execute

Somehow I need to tell the sqlite driver not to try to decode the text as UTF-8 (at least not using the standard algorithm, but it needs to use my fail-safe variant).

Answer 1

The solution in sqlite is to change the text_factory to something like: lambda x: unicode(x, "utf-8", "ignore")

However, I don't know how to tell the Django model driver this.

Have you tried

from django.db import connection
connection.connection.text_factory = lambda x: unicode(x, "utf-8", "ignore")

before running any queries?

Answer 2

Inspired by Milla's answer, consider the following monkey-patch that installs a more tolerant text_factory into the django sqlite connection. To be used when you cannot control how text is added to the sqlite database and it might not be in utf-8. Of course, the encoding used here may not be the right one, but at least your application won't crash.

import types
from django.db.backends.sqlite3.base import DatabaseWrapper

def to_unicode( s ):
    ''' Try a number of encodings in an attempt to convert the text to unicode. '''
    if isinstance( s, unicode ):
        return s
    if not isinstance( s, str ):
        return unicode(s)

    # Put the encodings you expect here in sequence.
    # Right-to-left charsets are not included in the following list.
    # Not all of these may be necessary - don't know.
    encodings = (
        'utf-8',
        'iso-8859-1', 'iso-8859-2', 'iso-8859-3',
        'iso-8859-4', 'iso-8859-5',
        'iso-8859-7', 'iso-8859-8', 'iso-8859-9',
        'iso-8859-10', 'iso-8859-11',
        'iso-8859-13', 'iso-8859-14', 'iso-8859-15',
        'windows-1250', 'windows-1251', 'windows-1252',
        'windows-1253', 'windows-1254', 'windows-1255',
        'windows-1257', 'windows-1258',
        'utf-8',     # Include utf8 again for the final exception.
    )
    for encoding in encodings:
        try:
            return unicode( s, encoding )
        except UnicodeDecodeError as e:
            pass
    raise e

if not hasattr(DatabaseWrapper, 'get_new_connection_is_patched'):
    _get_new_connection = DatabaseWrapper.get_new_connection
    def _get_new_connection_tolerant(self, conn_params):
        conn = _get_new_connection( self, conn_params )
        conn.text_factory = to_unicode
        return conn

    DatabaseWrapper.get_new_connection = types.MethodType( _get_new_connection_tolerant, None, DatabaseWrapper )
    DatabaseWrapper.get_new_connection_is_patched = True