Django runserver 和 makemigration 失败，跟踪显示旧迁移

Question

今晚我向模型添加了一个字段，当我运行 makemigrations 时，它告诉我该字段不存在。我注意到跟踪中引用了以前的迁移。我尝试将另一个字段添加到不同的模型并且 makemigrations 工作正常。

不仅 makemigrations 失败了，runserver 也失败了。两者都具有先前的迁移，跟踪中的#37。我试图生成迁移#40。我手动创建了 40 号迁移，将我的字段放在 models.py 中，并成功运行迁移。 Runserver 然后也可以正常工作。

我试图深入了解为什么之前的迁移会导致该模型中的新 makemigrations 和 runserver 失败。我已经通过手动创建迁移脚本解决了这个问题，但让我担心的是以前的迁移导致了这个问题。为什么由于我尝试添加的确切字段不存在而导致新的 makemigration 尝试出错？

# Note: Model2 also happens to be my app name and I may have mistakenly put Model2 where I should have put app name. Since I'm struggling to read what is going on, I wasn't sure. 
Unhandled exception in thread started by <function wrapper at 0x1077b3e60>
Traceback (most recent call last):
  File "/Users/my-user-name/.virtualenvs/my-project-name/lib/python2.7/site-packages/django/utils/autoreload.py", line 222, in wrapper
    fn(*args, **kwargs)
  File "/Users/my-user-name/.virtualenvs/my-project-name/lib/python2.7/site-packages/django/core/management/commands/runserver.py", line 107, in inner_run
    self.check_migrations()
  File "/Users/my-user-name/.virtualenvs/my-project-name/lib/python2.7/site-packages/django/core/management/commands/runserver.py", line 159, in check_migrations
    executor = MigrationExecutor(connections[DEFAULT_DB_ALIAS])
  File "/Users/my-user-name/.virtualenvs/my-project-name/lib/python2.7/site-packages/django/db/migrations/executor.py", line 17, in __init__
    self.loader = MigrationLoader(self.connection)
  File "/Users/my-user-name/.virtualenvs/my-project-name/lib/python2.7/site-packages/django/db/migrations/loader.py", line 48, in __init__
    self.build_graph()
  File "/Users/my-user-name/.virtualenvs/my-project-name/lib/python2.7/site-packages/django/db/migrations/loader.py", line 173, in build_graph
    self.load_disk()
  File "/Users/my-user-name/.virtualenvs/my-project-name/lib/python2.7/site-packages/django/db/migrations/loader.py", line 103, in load_disk
    migration_module = import_module("%s.%s" % (module_name, migration_name))
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/importlib/__init__.py", line 37, in import_module
    __import__(name)
  File "/Users/my-user-name/Code/my-project-name/my-app/migrations/0037_auto_20150824_0114.py", line 8, in <module>
    class Migration(migrations.Migration):
  File "/Users/my-user-name/Code/my-project-name/my-app/migrations/0037_auto_20150824_0114.py", line 32, in Migration
    field=models.ForeignKey(default=model1_model2_through.objects.all()[0].pk, to='model2.model1_model2_through'),
  File "/Users/my-user-name/.virtualenvs/my-project-name/lib/python2.7/site-packages/django/db/models/query.py", line 177, in __getitem__
    return list(qs)[0]
  File "/Users/my-user-name/.virtualenvs/my-project-name/lib/python2.7/site-packages/django/db/models/query.py", line 141, in __iter__
    self._fetch_all()
  File "/Users/my-user-name/.virtualenvs/my-project-name/lib/python2.7/site-packages/django/db/models/query.py", line 966, in _fetch_all
    self._result_cache = list(self.iterator())
  File "/Users/my-user-name/.virtualenvs/my-project-name/lib/python2.7/site-packages/django/db/models/query.py", line 265, in iterator
    for row in compiler.results_iter():
  File "/Users/my-user-name/.virtualenvs/my-project-name/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 700, in results_iter
    for rows in self.execute_sql(MULTI):
  File "/Users/my-user-name/.virtualenvs/my-project-name/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 786, in execute_sql
    cursor.execute(sql, params)
  File "/Users/my-user-name/.virtualenvs/my-project-name/lib/python2.7/site-packages/django/db/backends/utils.py", line 81, in execute
    return super(CursorDebugWrapper, self).execute(sql, params)
  File "/Users/my-user-name/.virtualenvs/my-project-name/lib/python2.7/site-packages/django/db/backends/utils.py", line 65, in execute
    return self.cursor.execute(sql, params)
  File "/Users/my-user-name/.virtualenvs/my-project-name/lib/python2.7/site-packages/django/db/utils.py", line 94, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/Users/my-user-name/.virtualenvs/my-project-name/lib/python2.7/site-packages/django/db/backends/utils.py", line 65, in execute
    return self.cursor.execute(sql, params)
django.db.utils.ProgrammingError: column model2_model1_model2_through.test_boolean does not exist
LINE 1: ...nt_date", "model2_model1_model2_through"."deposit_date", "model2_model1...


class Model1(models.Model):
    tours = models.ManyToManyField( 'Model2', through='Model1_Model2_Through')
    ...
class Model2(models.Model):
    ...
class Model1_Model2_Through(models.Model):
    test_boolean = models.BooleanField(default=False)

Answer 1

之前的迁移（在本例中为 37 号）有一个用于计算默认值的查询集。 Makemigrations 会运行之前的迁移，因此您在早期迁移中的查询集代码可能会导致未来的 makemigrations 尝试失败，因为在早期时间点不存在的字段。

而不是在迁移中做这样的事情。

SomeModel.objects.all()

你应该做这样的事情，只指定迁移时实际可用的字段。

SomeModel.objects.all().only('field1', 'field2', 'field3')