Re: new installations tryout problem

On 26/06/2015 3:24 PM, Elim Qiu wrote:
> Installed django recently, followed the django tutorial pdf to some
> where arround page 20. But got problems...
>
> It's on ubuntu 14.04, I have ipython installed and the following command
> some how brings up ipython. And it will raise exception for command
> Question.objects.filter(question_text__startswith='What')
>
> I have to do double quotes instead:
> Question.objects.filter(question_text__startswith="What")
>
> But now I encountered the following error and need your help:

The last line of the traceback gives the answer ...

IntegrityError: (1048, "Column 'poll_id' cannot be null")

It's a long time since I looked at the tutorial but I seem to remember
that questions each belong to a poll. So create a poll first if you
haven't done so already and then make sure question is related to poll.

Try finding polls ...

<anything>.objects.all() returns a queryset even if there is only one
object in it.
https://docs.djangoproject.com/en/1.7/topics/db/queries/#retrieving-all-objects

Querysets are very clever because they don't hit the database until you
need the actual objects. If you slice the queryset or list it, it gets
evaluated and the objects it points to become available.

so ...

from polls.models import Poll
poll_qs = Poll.objects.all()

If there is at least one Poll object you can get it directly if you know
enough about it to specify it in a filter() or use
Poll.objects.get(id=1) (er .. that's not how you would normally do it)

<anything>.objects.get() returns one object (not a queryset) or a
DoesNotExist or MultipleObjectsReturned error so you really must specify
it properly.

In any case, having discovered the poll you are interested in, you need
a variable to represent it. So ...

p = poll_qs[0] # this slices the first object off the queryset

... and p is the first object in the queryset.

Now retrieve the question as you did previously but this time assign it
to a variable like this ...

> In [11]: q = Question.objects.get(pub_date__year=this_year)
> Out [12]: q

Now

q.poll = p
q.save()

... and that should stop the IntegrityError: (1048, "Column 'poll_id'
cannot be null")

With any luck.

hth

Mike

>
> elim@aLnx:mydjango$ python manage.py shell
> Python 2.7.6 (default, Mar 22 2014, 22:59:56)
> Type "copyright", "credits" or "license" for more information.
>
> IPython 1.2.1 -- An enhanced Interactive Python.
> ? -> Introduction and overview of IPython's features.
> %quickref -> Quick reference.
> help -> Python's own help system.
> object? -> Details about 'object', use 'object??' for extra details.
>
> In [1]: import django
>
> In [2]: django.setup()
>
> In [3]: from polls.models import Question, Choice
>
> In [4]: Question.objects.all()
> Out[4]: [<Question: What's up?>]
>
> In [5]: from django.utils import timezone
>
> In [6]: Question.objects.filter(id=1)
> Out[6]: [<Question: What's up?>]
>
> In [7]: Question.objects.filter(question_text__startswith="What")
> Out[7]: [<Question: What's up?>]
>
> In [8]: # Due to ipython instead of python shell, we need "What" instead
> of 'What'
>
> In [9]: this_year = timezone.now().year
>
> In [10]: this_year
> Out[10]: 2015
>
> In [11]: Question.objects.get(pub_date__year=this_year)
> Out[11]: <Question: What's up?>
>
> In [12]: # Question.objects.get(id=2) will raise: Traceback (most recent
> call last):
>
> In [13]: # ...
>
> In [14]: # DoesNotExist: Question matching query does not exist.
>
> In [15]: Question.objects.get(id=1)
> Out[15]: <Question: What's up?>
>
> In [16]: Question.objects.get(pk=1)
> Out[16]: <Question: What's up?>
>
> In [17]: q = Question.objects.get(pk=1)
>
> In [18]: q.was_published_recently()
> Out[18]: False
>
> In [19]: q
> Out[19]: <Question: What's up?>
>
> In [20]: # What False (In[18]) ?
>
> In [21]: q.choice_set.all()
> Out[21]: []
>
> In [22]: q.choice_set.create(choice_text='Not much', votes=0)
> ---------------------------------------------------------------------------
> IntegrityError Traceback (most recent call last)
> <ipython-input-22-eb4d4c16acae> in <module>()
> ----> 1 q.choice_set.create(choice_text='Not much', votes=0)
>
> /usr/local/lib/python2.7/dist-packages/django/db/models/fields/related.pyc
> in create(self, **kwargs)
> 748 kwargs[rel_field.name] = self.instance
> 749 db = router.db_for_write(self.model,
> instance=self.instance)
> --> 750 return super(RelatedManager,
> self.db_manager(db)).create(**kwargs)
> 751 create.alters_data = True
> 752
>
> /usr/local/lib/python2.7/dist-packages/django/db/models/manager.pyc in
> manager_method(self, *args, **kwargs)
> 125 def create_method(name, method):
> 126 def manager_method(self, *args, **kwargs):
> --> 127 return getattr(self.get_queryset(), name)(*args,
> **kwargs)
> 128 manager_method.__name__ = method.__name__
> 129 manager_method.__doc__ = method.__doc__
>
> /usr/local/lib/python2.7/dist-packages/django/db/models/query.pyc in
> create(self, **kwargs)
> 346 obj = self.model(**kwargs)
> 347 self._for_write = True
> --> 348 obj.save(force_insert=True, using=self.db)
> 349 return obj
> 350
>
> /usr/local/lib/python2.7/dist-packages/django/db/models/base.pyc in
> save(self, force_insert, force_update, using, update_fields)
> 708
> 709 self.save_base(using=using, force_insert=force_insert,
> --> 710 force_update=force_update,
> update_fields=update_fields)
> 711 save.alters_data = True
> 712
>
> /usr/local/lib/python2.7/dist-packages/django/db/models/base.pyc in
> save_base(self, raw, force_insert, force_update, using, update_fields)
> 736 if not raw:
> 737 self._save_parents(cls, using, update_fields)
> --> 738 updated = self._save_table(raw, cls, force_insert,
> force_update, using, update_fields)
> 739 # Store the database on which the object was saved
> 740 self._state.db = using
>
> /usr/local/lib/python2.7/dist-packages/django/db/models/base.pyc in
> _save_table(self, raw, cls, force_insert, force_update, using,
> update_fields)
> 820
> 821 update_pk = bool(meta.has_auto_field and not pk_set)
> --> 822 result = self._do_insert(cls._base_manager, using,
> fields, update_pk, raw)
> 823 if update_pk:
> 824 setattr(self, meta.pk.attname, result)
>
> /usr/local/lib/python2.7/dist-packages/django/db/models/base.pyc in
> _do_insert(self, manager, using, fields, update_pk, raw)
> 859 """
> 860 return manager._insert([self], fields=fields,
> return_id=update_pk,
> --> 861 using=using, raw=raw)
> 862
> 863 def delete(self, using=None):
>
> /usr/local/lib/python2.7/dist-packages/django/db/models/manager.pyc in
> manager_method(self, *args, **kwargs)
> 125 def create_method(name, method):
> 126 def manager_method(self, *args, **kwargs):
> --> 127 return getattr(self.get_queryset(), name)(*args,
> **kwargs)
> 128 manager_method.__name__ = method.__name__
> 129 manager_method.__doc__ = method.__doc__
>
> /usr/local/lib/python2.7/dist-packages/django/db/models/query.pyc in
> _insert(self, objs, fields, return_id, raw, using)
> 918 query = sql.InsertQuery(self.model)
> 919 query.insert_values(fields, objs, raw=raw)
> --> 920 return
> query.get_compiler(using=using).execute_sql(return_id)
> 921 _insert.alters_data = True
> 922 _insert.queryset_only = False
>
> /usr/local/lib/python2.7/dist-packages/django/db/models/sql/compiler.pyc
> in execute_sql(self, return_id)
> 969 with self.connection.cursor() as cursor:
> 970 for sql, params in self.as_sql():
> --> 971 cursor.execute(sql, params)
> 972 if not (return_id and cursor):
> 973 return
>
> /usr/local/lib/python2.7/dist-packages/django/db/backends/utils.pyc in
> execute(self, sql, params)
> 77 start = time()
> 78 try:
> ---> 79 return super(CursorDebugWrapper, self).execute(sql,
> params)
> 80 finally:
> 81 stop = time()
>
> /usr/local/lib/python2.7/dist-packages/django/db/backends/utils.pyc in
> execute(self, sql, params)
> 62 return self.cursor.execute(sql)
> 63 else:
> ---> 64 return self.cursor.execute(sql, params)
> 65
> 66 def executemany(self, sql, param_list):
>
> /usr/local/lib/python2.7/dist-packages/django/db/backends/mysql/base.pyc
> in execute(self, query, args)
> 127 # misclassified and Django would prefer the more
> logical place.
> 128 if e.args[0] in self.codes_for_integrityerror:
> --> 129 six.reraise(utils.IntegrityError,
> utils.IntegrityError(*tuple(e.args)), sys.exc_info()[2])
> 130 raise
> 131
>
> /usr/local/lib/python2.7/dist-packages/django/db/backends/mysql/base.pyc
> in execute(self, query, args)
> 122 try:
> 123 # args is None means no string interpolation
> --> 124 return self.cursor.execute(query, args)
> 125 except Database.OperationalError as e:
> 126 # Map some error codes to IntegrityError, since
> they seem to be
>
> /usr/lib/python2.7/dist-packages/MySQLdb/cursors.pyc in execute(self,
> query, args)
> 172 del tb
> 173 self.messages.append((exc, value))
> --> 174 self.errorhandler(self, exc, value)
> 175 self._executed = query
> 176 if not self._defer_warnings: self._warning_check()
>
> /usr/lib/python2.7/dist-packages/MySQLdb/connections.pyc in
> defaulterrorhandler(***failed resolving arguments***)
> 34 del cursor
> 35 del connection
> ---> 36 raise errorclass, errorvalue
> 37
> 38 re_numeric_part = re.compile(r"^(\d+)")
>
> IntegrityError: (1048, "Column 'poll_id' cannot be null")
>

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