python - 使用 Django 将 BrinIndex 添加到现有的 PostgreSQL 数据库

Question

我正在使用 Django 运行一个网站，其中的数据库在 PostgreSQL 上运行。为了提高性能，我想将 BrinIndex 添加到在磁盘上自然排序的模型中。

我已将索引添加到我的模型定义中，如下所示。

from django.contrib.postgres.indexes import BrinIndex

class Measurement(models.Model):
    class Meta:
        indexes = (
            BrinIndex(fields=['time'])
        )

    time = models.DateTimeField(
        'Time of measurement',
        null=True
    )

但是正在运行

python3 manage.py makemigrations

返回错误

Traceback (most recent call last):
  File "C:\Program Files\JetBrains\PyCharm 2018.1.1\helpers\pycharm\django_manage.py", line 52, in <module>
    run_command()
  File "C:\Program Files\JetBrains\PyCharm 2018.1.1\helpers\pycharm\django_manage.py", line 46, in run_command
    run_module(manage_file, None, '__main__', True)
  File "C:\Python36\lib\runpy.py", line 205, in run_module
    return _run_module_code(code, init_globals, run_name, mod_spec)
  File "C:\Python36\lib\runpy.py", line 96, in _run_module_code
    mod_name, mod_spec, pkg_name, script_name)
  File "C:\Python36\lib\runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "C:/Users/*USERNAME*/*PROJECT_NAME*\manage.py", line 22, in <module>
    execute_from_command_line(sys.argv)
  File "C:\Users\*USERNAME*\*PROJECT_NAME*\venv\lib\site-packages\django\core\management\__init__.py", line 371, in execute_from_command_line
    utility.execute()
  File "C:\Users\*USERNAME*\*PROJECT_NAME*\venv\lib\site-packages\django\core\management\__init__.py", line 347, in execute
    django.setup()
  File "C:\Users\*USERNAME*\*PROJECT_NAME*\venv\lib\site-packages\django\__init__.py", line 24, in setup
    apps.populate(settings.INSTALLED_APPS)
  File "C:\Users\*USERNAME*\*PROJECT_NAME*\venv\lib\site-packages\django\apps\registry.py", line 112, in populate
    app_config.import_models()
  File "C:\Users\*USERNAME*\*PROJECT_NAME*\venv\lib\site-packages\django\apps\config.py", line 198, in import_models
    self.models_module = import_module(models_module_name)
  File "C:\Python36\lib\importlib\__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 978, in _gcd_import
  File "<frozen importlib._bootstrap>", line 961, in _find_and_load
  File "<frozen importlib._bootstrap>", line 950, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 655, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 678, in exec_module
  File "<frozen importlib._bootstrap>", line 205, in _call_with_frames_removed
  File "C:/Users/*USERNAME*/*PROJECT_NAME*\*APP_NAME*\models.py", line 300, in <module>
    class Measurement(models.Model):
  File "C:\Users\*USERNAME*\*PROJECT_NAME*\venv\lib\site-packages\django\db\models\base.py", line 298, in __new__
    new_class._meta.indexes = [copy.deepcopy(idx) for idx in new_class._meta.indexes]
TypeError: 'BrinIndex' object is not iterable

我做错了什么吗？这个索引以后可以不加吗？

Answer 1

这是你代码的问题当用单个值定义元组时，你必须在值的末尾加上“，”，否则 python 不会将其识别为元组，例如:

a = ('value1') #is a string not a tuple
a = ('value1',) #is a tuple 

您的代码应该如下所示:从 django.contrib.postgres.indexes 导入 BrinIndex

class Measurement(models.Model):
    class Meta:
        indexes = (
            BrinIndex(fields=['time']),  # "," is added here
        )

    time = models.DateTimeField(
        'Time of measurement',
        null=True
    )