CODEWITHSUNDEEP
pythonmysqldjangomodelforeign-keys
cybertextron
cybertextron

Reputation: 10961

Defining relationships across Multiple Models - Django

I have the following relationship between three Django models:

  class TestCase(models.Model):
       '''
       Define the testcase model. A testcase is a python Class
       which contains a set of tests
       '''
       name = models.BinaryField(blank=False)
       filename = models.BinaryField(blank=True)
       run_flag = models.IntegerField(default=0)
       run_as_root = models.BooleanField(default=0)
       num_tests = models.IntegerField(default=0)
       testsuite = models.ForeignKey(TestSuite)

       def __str__(self):
           return self.name

Please ignore TestSuite: it's not important for this problem. Every TestCase is what you may imagine: a TestCase (class). So every time one executes a TestCase it has a TestExecution and a Result:

  class Result(models.Model):
       '''
       Define the result of a testcase. It may be 'PASS', 'FAIL',
       'SKIPPED' or 'ABORTED'
       '''
       FAIL = 0
       PASS = 1
       ABORTED = 2
       SKIPPED = 3

       Status = (
           (PASS, 'PASS'),
           (FAIL, 'FAIL'),
           (SKIPPED, 'SKIPPED'),
           (ABORTED, 'ABORTED'),
       )

       status = models.IntegerField(choices=Status, default=FAIL)

       testcase = models.ForeignKey(TestCase)


   class TestExecution(models.Model):

       name = models.BinaryField(blank=False)
       num_testsuites = models.IntegerField(default=0)
       time = models.FloatField()
       date = models.DateTimeField(default=django.utils.timezone.now)

      result = models.OneToOneField(Result)

      def __str__(self):
          return self.name + " : " + self.date + " : " + self.time

That can be said, a TestCase hasMany Result but the relationship between Result and TestExecution is OneToOne. I'm having some problems with my models schema. I know a simple solution would be to merge the tables Result and TestExecution:

    python manage.py migrate
Operations to perform:
  Synchronize unmigrated apps: staticfiles, messages
  Apply all migrations: admin, autotester, contenttypes, auth, sessions
Synchronizing apps without migrations:
  Creating tables...
    Running deferred SQL...
  Installing custom SQL...
Running migrations:
  Rendering model states... DONE
  Applying autotester.0005_auto_20150519_1831...Traceback (most recent call last):
  File "manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/__init__.py", line 338, in execute_from_command_line
    utility.execute()
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/__init__.py", line 330, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/base.py", line 390, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/base.py", line 441, in execute
    output = self.handle(*args, **options)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/commands/migrate.py", line 221, in handle
    executor.migrate(targets, plan, fake=fake, fake_initial=fake_initial)
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/executor.py", line 110, in migrate
    self.apply_migration(states[migration], migration, fake=fake, fake_initial=fake_initial)
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/executor.py", line 147, in apply_migration
    state = migration.apply(state, schema_editor)
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/migration.py", line 115, in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/operations/fields.py", line 62, in database_forwards
    field,
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/mysql/schema.py", line 43, in add_field
    super(DatabaseSchemaEditor, self).add_field(model, field)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/base/schema.py", line 403, in add_field
    self.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/base/schema.py", line 111, in execute
    cursor.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/utils.py", line 79, in execute
    return super(CursorDebugWrapper, self).execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/utils.py", line 97, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/mysql/base.py", line 124, in execute
    return self.cursor.execute(query, args)
  File "/usr/local/lib/python2.7/dist-packages/MySQLdb/cursors.py", line 205, in execute
    self.errorhandler(self, exc, value)
  File "/usr/local/lib/python2.7/dist-packages/MySQLdb/connections.py", line 36, in defaulterrorhandler
    raise errorclass, errorvalue
django.db.utils.IntegrityError: (1062, "Duplicate entry '0' for key 'result_id'")

What's the most appropriate way to proceed regarding the models schema?

Adding the autotester/migrations/0005_auto_20150519_1831.py as per request:

# -- coding: utf-8 -- from future import unicode_literals

from django.db import models, migrations

class Migration(migrations.Migration):

    dependencies = [
       ('autotester', '0004_auto_20150519_1744'),
   ]

   operations = [
       migrations.RemoveField(
           model_name='testexecution',
           name='framework',
       ),
       migrations.AddField(
           model_name='testexecution',
           name='result',
           field=models.OneToOneField(default=None, to='autotester.Result'),
           preserve_default=False,
       ),
   ]

Upvotes: 4

Views: 138

Answers (1)

Charlesthk
Charlesthk

Reputation: 9684

A OneToOneField is a like a ForeignKey with unique=True.

You problem comes with this unique constraint since you can't add a field with a unique constraint if your database is not empty. What you have to do is:

  1. add the field without a unique constraint = ForeignKey
  2. Fill this field regarding the upcoming unique constraint you will have
  3. Change the ForeignKey to a OneToOneField

Here are the detailed steps:

First step:

Delete your autotester/migrations/0005_auto_20150519_1831.py file and change your result field with result = models.ForeignKey(Result, null=True, blank=True) in your TestExecution model and do the migration:

./manage.py makemigrations autotester
./manage.py migrate autotester

Second Step:

For every Result you have, create a TestExecution (replace FOO with the appropriate datas):

results = Result.objects.all()

for result in results:
    tst = TestExecution()
    tst.name = FOO
    tst. num_testsuites = FOO
    tst.time = FOO
    tst.result_id = result.id
    tst.save()

Third step

Change your result field with result = models.OneToOneField(Result) and then do the migration:

./manage.py makemigrations autotester
./manage.py migrate autotester

You should be good to go.

Upvotes: 2

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