django: can't adapt error when importing data from postgres database

Question

Hi,

I'm having strange error with installing fixture from dumped data. I am using psycopg2, and django1.1.1

silver:probsbox oleg$ python manage.py loaddata /Users/oleg/probs.json 
Installing json fixture '/Users/oleg/probs' from '/Users/oleg/probs'.
Problem installing fixture '/Users/oleg/probs.json': Traceback (most recent call last):
  File "/opt/local/lib/python2.5/site-packages/django/core/management/commands/loaddata.py", line 153, in handle
    obj.save()
  File "/opt/local/lib/python2.5/site-packages/django/core/serializers/base.py", line 163, in save
    models.Model.save_base(self.object, raw=True)
  File "/opt/local/lib/python2.5/site-packages/django/db/models/base.py", line 495, in save_base
    result = manager._insert(values, return_id=update_pk)
  File "/opt/local/lib/python2.5/site-packages/django/db/models/manager.py", line 177, in _insert
    return insert_query(self.model, values, **kwargs)
  File "/opt/local/lib/python2.5/site-packages/django/db/models/query.py", line 1087, in insert_query
    return query.execute_sql(return_id)
  File "/opt/local/lib/python2.5/site-packages/django/db/models/sql/subqueries.py", line 320, in execute_sql
    cursor = super(InsertQuery, self).execute_sql(None)
  File "/opt/local/lib/python2.5/site-packages/django/db/models/sql/query.py", line 2369, in execute_sql
    cursor.execute(sql, params)
  File "/opt/local/lib/python2.5/site-packages/django/db/backends/util.py", line 19, in execute
    return self.cursor.execute(sql, params)
ProgrammingError: can't adapt

First I've checked similar issues on internet. This one seemed to be very related: http://code.djangoproject.com/ticket/5996, as my data has many non ASCII symbols

But actually I've checked my django installation and it's ok there

Could you advice what is wrong

====

Continued investigation after added print statement as suggested by the first answer. Log looks this way:

silver:probsbox oleg$ python manage.py loaddata /Users/oleg/probs.json 
Installing json fixture '/Users/oleg/probs' from '/Users/oleg/probs'.
<DeserializedObject: Novice>
<DeserializedObject: Junior>
<DeserializedObject: Chess enthusiast>
<DeserializedObject: Experienced player >
<DeserializedObject: Smart player>
Problem installing fixture '/Users/oleg/probs.json': Traceback (most recent call last):
  File "/opt/local/lib/python2.5/site-packages/django/core/management/commands/loaddata.py", line 153, in handle
    print obj
  File "/opt/local/lib/python2.5/site-packages/django/core/serializers/base.py", line 155, in __repr__
    return "<DeserializedObject: %s>" % smart_str(self.object)
  File "/opt/local/lib/python2.5/site-packages/django/utils/encoding.py", line 107, in smart_str
    return str(s)
  File "/opt/local/lib/python2.5/site-packages/django/db/models/base.py", line 335, in __str__
    return force_unicode(self).encode('utf-8')
  File "/opt/local/lib/python2.5/site-packages/django/utils/encoding.py", line 71, in force_unicode
    s = unicode(s)
  File "/Users/oleg/Sites/probsbox/registration/models.py", line 58, in __unicode__
    return u"%s's profile" %(self.user.username)
  File "/opt/local/lib/python2.5/site-packages/django/db/models/fields/related.py", line 257, in __get__
    rel_obj = QuerySet(self.field.rel.to).get(**params)
  File "/opt/local/lib/python2.5/site-packages/django/db/models/query.py", line 305, in get
    % self.model._meta.object_name)
DoesNotExist: User matching query does not exist.

silver:probsbox oleg$ 

Error from very last comment

<DeserializedObject: qwert2000's profile>

Problem installing fixture '/Users/oleg/probs.json': Traceback (most recent call last): File "/opt/local/lib/python2.5/site-packages/django/core/management/commands/loaddata.py", line 154, in handle obj.save() File "/opt/local/lib/python2.5/site-packages/django/core/serializers/base.py", line 163, in save models.Model.save_base(self.object, raw=True) File "/opt/local/lib/python2.5/site-packages/django/db/models/base.py", line 495, in save_base result = manager._insert(values, return_id=update_pk) File "/opt/local/lib/python2.5/site-packages/django/db/models/manager.py", line 177, in _insert return insert_query(self.model, values, **kwargs) File "/opt/local/lib/python2.5/site-packages/django/db/models/query.py", line 1087, in insert_query return query.execute_sql(return_id) File "/opt/local/lib/python2.5/site-packages/django/db/models/sql/subqueries.py", line 320, in execute_sql cursor = super(InsertQuery, self).execute_sql(None) File "/opt/local/lib/python2.5/site-packages/django/db/models/sql/query.py", line 2369, in execute_sql cursor.execute(sql, params) File "/opt/local/lib/python2.5/site-packages/django/db/backends/util.py", line 19, in execute return self.cursor.execute(sql, params) ProgrammingError: can't adapt

Answer 1

The can't adapt error is raised by psycopg2 when it receives an data type that it doesn't know how to translate into a value for a SQL statement. For example, if you accidentally pass a list, say, for a value that is supposed to be an integer, psycopg2 will raise this can't adapt error.

The faq.txt document that ships with the source distribution of psycopg2 explains it this way:

Why does !cursor.execute() raise the exception can't adapt?

Psycopg converts Python objects in a SQL string representation by looking at the object class. The exception is raised when you are trying to pass as query parameter an object for which there is no adapter registered for its class. See :ref:adapting-new-types for informations.

Probably your best first-pass at finding the offending value is to run loaddata in fully verbose mode: python manage.py loaddata --verbosity=2 /Users/oleg/probs.json

Well, I was hoping loaddata verbosity would work and I wouldn't have to confess that I've never found an elegant way of debugging adaptation errors with django's loaddata. In the past, I've resorted to inserting print statements in django's loaddata function so that I can see the values being deserialized when the error occurs. I've edited django/core/management/loaddata.py. Look of obj.save() in the handle() function. I hope this confession inspires someone to share a better solution :-)

Answer 2

Ok, I ended copying dump from my database, and restoring it locally without python...