“no such column” after adding a field to the model

Question

environment DJANGO VERSION 1.9 Python 2.7.6

I added a field (scores) to a model class in models.py like this

from django.db import models
from django         


        

Answer 1

This can happen if you are referencing your model at the root level of your app

This happened to me when I was updating the app mapping_master. I was adding a new field like so:

class MappingMaster(models.Model):

    ...

    # New field that was being added
    statement = models.CharField(max_length=20, choices=STATEMENT_CHOICES, default='PNL', blank=True, null=True)

Gave me the following stacktrace:

D:\Adwaith\codebase\unitapp>python manage.py makemigrations
Traceback (most recent call last):
  File "manage.py", line 10, in 
    execute_from_command_line(sys.argv)
  File "C:\Python27\lib\site-packages\django\core\management\__init__.py", line
338, in execute_from_command_line
    utility.execute()
  File "C:\Python27\lib\site-packages\django\core\management\__init__.py", line
312, in execute
    django.setup()

....
....

  File "C:\Python27\lib\site-packages\django\apps\config.py", line 198, in impor
t_models
    self.models_module = import_module(models_module_name)
  File "C:\Python27\lib\importlib\__init__.py", line 37, in import_module
    __import__(name)
  File "D:\Adwaith\codebase\unitapp\trial_balance_entry\models.py", line 5, in <
module>
    from unitapp import docclass
  File "D:\Adwaith\codebase\unitapp\unitapp\docclass.py", line 139, in 
    sample_train_type(type_classifier)
  File "D:\Adwaith\codebase\unitapp\unitapp\docclass.py", line 6, in sample_trai
n_type
    for mapping in MappingMaster.objects.all():

....
....

  File "C:\Python27\lib\site-packages\django\db\backends\sqlite3\base.py", line
318, in execute
    return Database.Cursor.execute(self, query, params)
django.db.utils.OperationalError: no such column: mapping_master_mappingmaster.statement

Turns out that my problem was in another file entirely. It was in the trial_balance_entry app:

...
# The important line is below
from unitapp import docclass


class TrialBalanceEntry(models.Model):
    ...

And inside docclass.py, I had:

import re, csv, os
from mapping_master.models import MappingMaster


def sample_train_type(cl):
    for mapping in MappingMaster.objects.all():
        cl.train(mapping.entry, mapping.type)


def sample_train_category(cl):
    for mapping in MappingMaster.objects.all():
        cl.train(mapping.entry, mapping.category)

...

Turns out that the MappingMaster model instances were being referenced at the root of the app (since I imported it at the start of the file in the models file in trial_balance_entry.

I fixed that by moving the import to one of the inner methods of my TrialBalanceEntry model. This made sure I didn't have any hidden circular dependencies.

P.S. From next time, please provide a stacktrace from the console so we can debug it more easily.