Greetings,
My organization is evaluating Django as a possible frontend to a
legacy IBM Db2 Database. I've successfully connected the Django 1.2
beta with our database, but ran into an issue with a DB2 specific
column.
Our tables all have primary keys defined as `CHAR(13) FOR BIT DATA`,
which is essentially a binary type (db2 has a built-in function to
generate these in lieu of an auto-increment column). I created a
custom type in Django, and used the `binascii` module in python to
pack/unpack the binary data (this much is known to work). I have a
working SQLAlchemy example that works in largely the same way. Here's
a very simple example of what's going on:
class TechIdField(models.Field):
description = "A Python type to translate CHAR FOR BIT DATA
fields to strings"
def __init__ (self, *args, **kwargs):
super(TechIdField, self).__init__(*args, **kwargs)
def db_type(self, connection):
return 'CHAR(13) FOR BIT DATA'
def to_python(self, value):
return b2a_hex(value)
def get_db_prep_value(self, value):
return a2b_hex(value)
class TestModel(models.Model):
tech_id = TechIdField(primary_key=True)
pref_name = models.CharField(max_length=20)
pref_value = models.CharField(max_length=100)
class Meta:
db_table = 'test_model'
When I try to run a query in the Django shell, the database backend
bombs out because it attempts to convert the value that my custom type
just packed to a unicode string. Here's an example from a manage.py
shell session:
>>> from testapp import models;
>>>
models.TestModel.objects.filter(tech_id='20070618193649842630000000')
Traceback (most recent call last):
File "<console>", line 1, in <module>
File "/usr/local/lib/python2.5/site-packages/django/db/models/
query.py", line 66, in __repr__
data = list(self[:REPR_OUTPUT_SIZE + 1])
File "/usr/local/lib/python2.5/site-packages/django/db/models/
query.py", line 81, in __len__
self._result_cache.extend(list(self._iter))
File "/usr/local/lib/python2.5/site-packages/django/db/models/
query.py", line 267, in iterator
for row in compiler.results_iter():
File "/usr/local/lib/python2.5/site-packages/django/db/models/
sql/compiler.py", line 685, in results_iter
for rows in self.execute_sql(MULTI):
File "/usr/local/lib/python2.5/site-packages/django/db/models/
sql/compiler.py", line 740, in execute_sql
cursor.execute(sql, params)
File "/usr/local/lib/python2.5/site-packages/django/db/backends/
util.py", line 22, in execute
sql = self.db.ops.last_executed_query(self.cursor, sql,
params)
File "/usr/local/lib/python2.5/site-packages/django/db/backends/
__init__.py", line 211, in last_executed_query
u_params = tuple([to_unicode(val) for val in params])
File "/usr/local/lib/python2.5/site-packages/django/db/backends/
__init__.py", line 209, in <lambda>
to_unicode = lambda s: force_unicode(s, strings_only=True)
File "/usr/local/lib/python2.5/site-packages/django/utils/
encoding.py", line 92, in force_unicode
raise DjangoUnicodeDecodeError(s, *e.args)
DjangoUnicodeDecodeError: 'utf8' codec can't decode byte 0x84 in
position 7: unexpected code byte. You passed in ' \x07\x06\x18\x196I
\x84&0\x00\x00\x00' (<type 'str'>)
I sifted through the trac tickets a bit and this is exactly what was
reported in #6416, which was unfortunately closed without being
resolved.
I'd love to keep Django in the mix as a possible framework for us.
Could anyone suggest a workaround? This would pose a pretty big
problem for us, unfortunately, since almost every query we make will
have one or more of these ID's. I'm obviously new to Django as a
whole, so it's quite likely there is a better way for me to go about
getting Django to understand and deal with this column type.
Any help would be much appreciated.
Cheers,
Brandon
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