删除数据库和迁移后无法从模型（makemigrations）创建数据库

Question

我删除了整个数据库并重新创建数据库，并从应用程序和项目的根文件夹（以及迁移文件夹中删除了pycache文件夹）。

我试图创建模型的数据库结构如下： $ python manage.py makemigrations

这我得到了，可惜没有什么至今帮助过我的错误：

The above exception was the direct cause of the following exception: 

Traceback (most recent call last): 
    File "manage.py", line 10, in <module> 
    execute_from_command_line(sys.argv) 
    File "/Users/olegbelousov/.virtualenvs/photobasa/lib/python3.5/site-packages/django/core/management/__init__.py", line 353, in execute_from_command_line 
    utility.execute() 
    File "/Users/olegbelousov/.virtualenvs/photobasa/lib/python3.5/site-packages/django/core/management/__init__.py", line 327, in execute 
    django.setup() 
    File "/Users/olegbelousov/.virtualenvs/photobasa/lib/python3.5/site-packages/django/__init__.py", line 18, in setup 
    apps.populate(settings.INSTALLED_APPS) 
    File "/Users/olegbelousov/.virtualenvs/photobasa/lib/python3.5/site-packages/django/apps/registry.py", line 108, in populate 
    app_config.import_models(all_models) 
    File "/Users/olegbelousov/.virtualenvs/photobasa/lib/python3.5/site-packages/django/apps/config.py", line 202, in import_models 
    self.models_module = import_module(models_module_name) 
    File "/Users/olegbelousov/.virtualenvs/photobasa/lib/python3.5/importlib/__init__.py", line 126, in import_module 
    return _bootstrap._gcd_import(name[level:], package, level) 
    File "<frozen importlib._bootstrap>", line 986, in _gcd_import 
    File "<frozen importlib._bootstrap>", line 969, in _find_and_load 
    File "<frozen importlib._bootstrap>", line 958, in _find_and_load_unlocked 
    File "<frozen importlib._bootstrap>", line 673, in _load_unlocked 
    File "<frozen importlib._bootstrap_external>", line 662, in exec_module 
    File "<frozen importlib._bootstrap>", line 222, in _call_with_frames_removed 
    File "/Users/olegbelousov/dev/photobase/proto/models.py", line 100, in <module> 
    class Photo(TimeStampedModel, SoftDeletableModel): 
    File "/Users/olegbelousov/dev/photobase/proto/models.py", line 101, in Photo 
    PHOTOGRAPHER_COUNT = Photographer.objects.count() 
    File "/Users/olegbelousov/.virtualenvs/photobasa/lib/python3.5/site-packages/django/db/models/manager.py", line 122, in manager_method 
    return getattr(self.get_queryset(), name)(*args, **kwargs) 
    File "/Users/olegbelousov/.virtualenvs/photobasa/lib/python3.5/site-packages/django/db/models/query.py", line 371, in count 
    return self.query.get_count(using=self.db) 
    File "/Users/olegbelousov/.virtualenvs/photobasa/lib/python3.5/site-packages/django/db/models/sql/query.py", line 483, in get_count 
    number = obj.get_aggregation(using, ['__count'])['__count'] 
    File "/Users/olegbelousov/.virtualenvs/photobasa/lib/python3.5/site-packages/django/db/models/sql/query.py", line 464, in get_aggregation 
    result = compiler.execute_sql(SINGLE) 
    File "/Users/olegbelousov/.virtualenvs/photobasa/lib/python3.5/site-packages/django/db/models/sql/compiler.py", line 848, in execute_sql 
    cursor.execute(sql, params) 
    File "/Users/olegbelousov/.virtualenvs/photobasa/lib/python3.5/site-packages/django/db/backends/utils.py", line 79, in execute 
    return super(CursorDebugWrapper, self).execute(sql, params) 
    File "/Users/olegbelousov/.virtualenvs/photobasa/lib/python3.5/site-packages/django/db/backends/utils.py", line 64, in execute 
    return self.cursor.execute(sql, params) 
    File "/Users/olegbelousov/.virtualenvs/photobasa/lib/python3.5/site-packages/django/db/utils.py", line 95, in __exit__ 
    six.reraise(dj_exc_type, dj_exc_value, traceback) 
    File "/Users/olegbelousov/.virtualenvs/photobasa/lib/python3.5/site-packages/django/utils/six.py", line 685, in reraise 
    raise value.with_traceback(tb) 
    File "/Users/olegbelousov/.virtualenvs/photobasa/lib/python3.5/site-packages/django/db/backends/utils.py", line 64, in execute 
    return self.cursor.execute(sql, params) 
django.db.utils.ProgrammingError: relation "proto_photographer" does not exist 
LINE 1: SELECT COUNT(*) AS "__count" FROM "proto_photographer" 
             ^

Answer 1

makemigrations检查分贝查看自项目中每个应用上次迁移以来是否发生了更改。为了这个功能，你的Django项目必须能够成功开始运行。如果有前面的表丢失，这不会发生。

运行python manage.py migrate运行所有现有迁移并使数据库进入上一组迁移所存储的状态。之后，您应该能够运行python manage.py makemigrations以创建新的迁移，然后再次将它们与python manage.py migrate一起应用。