Question

我在 Django 中使用了多个数据库，并在 settings.py 中连接了默认的 SQLite 和 PostgreSQL 数据库。

设置.py:

DATABASE_ROUTERS = ['routers.db_routers.AppRouter']
DATABASE_APPS_MAPPING = {'product': 'postgres',}

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': BASE_DIR / 'db.sqlite3',
    },
    'postgres': {
        'ENGINE': 'django.db.backends.postgresql',
        'NAME': 'product',
        'USER': 'postgres',
        'PASSWORD':'password',
        'HOST':'localhost'
    }

}

并在 routers 文件夹中创建了 db_routers.py：

class AppRouter:
    """
    A router to control all database operations on models in the
    product application.
    """
    def db_for_read(self, model, **hints):
        """
        Attempts to read user models go to postgres.
        """
        if model._meta.app_label == 'product':
            return 'postgres'
        return 'default'

    def db_for_write(self, model, **hints):
        """
        Attempts to write user models go to postgres.
        """
        if model._meta.app_label == 'product':
            return 'postgres'
        return 'default'

    def allow_relation(self, obj1, obj2, **hints):
        """
        Allow relations if a model in the user app is involved.
        """
        if obj1._meta.app_label == 'product' or \
           obj2._meta.app_label == 'product':
           return True
        elif 'product' not in [obj1._meta.app_label, obj2._meta.app_label]:
            return True

        return None


    def allow_migrate(self, db, app_label, model_name=None, **hints):
        """
        Make sure the auth app only appears in the 'product_db'
        database.
        """
        if app_label == 'product':
            return db == 'postgres'
        return None

这里是model.py：

class Product(models.Model):
    name = models.CharField(max_length=100)
    price = models.DecimalField(max_digits=10, decimal_places=2)
    weight = models.DecimalField(max_digits=10, decimal_places=2)
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)
    
    class Meta:
        app_label = 'product'
    
    def __str__(self):
        return self.name

我通过运行 python3 manage.py makemigrations 成功制作了表格，但是当我尝试使用 python3 manage.py migrate --database=postgres 进行迁移时，我收到此错误： ProgrammingError: relation "product" does not exist. SELECT COUNT(*) AS "__count" FROM "product"并且该表格也不存在于 PgAdmin 中。

产品的迁移.py：

# Generated by Django 3.2.5 on 2021-07-16 13:25

from django.db import migrations, models


class Migration(migrations.Migration):

    initial = True

    dependencies = [
    ]

    operations = [
        migrations.CreateModel(
            name='Product',
            fields=[
                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
                ('name', models.CharField(max_length=100)),
                ('price', models.DecimalField(decimal_places=2, max_digits=10)),
                ('weight', models.DecimalField(decimal_places=2, max_digits=10)),
                ('created_at', models.DateTimeField(auto_now_add=True)),
                ('updated_at', models.DateTimeField(auto_now=True)),
            ],
            options={
                'db_table': 'product',
                'managed': False,
            },
        ),
    ]

错误：

Environment:


Request Method: GET
Request URL: http://127.0.0.1:8000/api/product/

Django Version: 3.2.5
Python Version: 3.8.10
Installed Applications:
['django.contrib.admin',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.messages',
 'django.contrib.staticfiles',
 'rest_framework',
 'rest_framework.authtoken',
 'post',
 'product']
Installed Middleware:
['django.middleware.security.SecurityMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.common.CommonMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'django.middleware.clickjacking.XFrameOptionsMiddleware']



Traceback (most recent call last):
  File "/home/rudrakshi/Desktop/Rose/assignment/env/lib/python3.8/site-packages/django/db/backends/utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)

The above exception (relation "product" does not exist
LINE 1: ...product"."created_at", "product"."updated_at" FROM "product"
                                                              ^
) was the direct cause of the following exception:
  File "/home/rudrakshi/Desktop/Rose/assignment/env/lib/python3.8/site-packages/django/core/handlers/exception.py", line 47, in inner
    response = get_response(request)
  File "/home/rudrakshi/Desktop/Rose/assignment/env/lib/python3.8/site-packages/django/core/handlers/base.py", line 181, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/home/rudrakshi/Desktop/Rose/assignment/env/lib/python3.8/site-packages/django/views/decorators/csrf.py", line 54, in wrapped_view
    return view_func(*args, **kwargs)
  File "/home/rudrakshi/Desktop/Rose/assignment/env/lib/python3.8/site-packages/django/views/generic/base.py", line 70, in view
    return self.dispatch(request, *args, **kwargs)
  File "/home/rudrakshi/Desktop/Rose/assignment/env/lib/python3.8/site-packages/rest_framework/views.py", line 509, in dispatch
    response = self.handle_exception(exc)
  File "/home/rudrakshi/Desktop/Rose/assignment/env/lib/python3.8/site-packages/rest_framework/views.py", line 469, in handle_exception
    self.raise_uncaught_exception(exc)
  File "/home/rudrakshi/Desktop/Rose/assignment/env/lib/python3.8/site-packages/rest_framework/views.py", line 480, in raise_uncaught_exception
    raise exc
  File "/home/rudrakshi/Desktop/Rose/assignment/env/lib/python3.8/site-packages/rest_framework/views.py", line 506, in dispatch
    response = handler(request, *args, **kwargs)
  File "/home/rudrakshi/Desktop/Rose/assignment/env/lib/python3.8/site-packages/rest_framework/generics.py", line 239, in get
    return self.list(request, *args, **kwargs)
  File "/home/rudrakshi/Desktop/Rose/assignment/env/lib/python3.8/site-packages/rest_framework/mixins.py", line 46, in list
    return Response(serializer.data)
  File "/home/rudrakshi/Desktop/Rose/assignment/env/lib/python3.8/site-packages/rest_framework/serializers.py", line 745, in data
    ret = super().data
  File "/home/rudrakshi/Desktop/Rose/assignment/env/lib/python3.8/site-packages/rest_framework/serializers.py", line 246, in data
    self._data = self.to_representation(self.instance)
  File "/home/rudrakshi/Desktop/Rose/assignment/env/lib/python3.8/site-packages/rest_framework/serializers.py", line 663, in to_representation
    return [
  File "/home/rudrakshi/Desktop/Rose/assignment/env/lib/python3.8/site-packages/django/db/models/query.py", line 280, in __iter__
    self._fetch_all()
  File "/home/rudrakshi/Desktop/Rose/assignment/env/lib/python3.8/site-packages/django/db/models/query.py", line 1324, in _fetch_all
    self._result_cache = list(self._iterable_class(self))
  File "/home/rudrakshi/Desktop/Rose/assignment/env/lib/python3.8/site-packages/django/db/models/query.py", line 51, in __iter__
    results = compiler.execute_sql(chunked_fetch=self.chunked_fetch, chunk_size=self.chunk_size)
  File "/home/rudrakshi/Desktop/Rose/assignment/env/lib/python3.8/site-packages/django/db/models/sql/compiler.py", line 1175, in execute_sql
    cursor.execute(sql, params)
  File "/home/rudrakshi/Desktop/Rose/assignment/env/lib/python3.8/site-packages/django/db/backends/utils.py", line 98, in execute
    return super().execute(sql, params)
  File "/home/rudrakshi/Desktop/Rose/assignment/env/lib/python3.8/site-packages/django/db/backends/utils.py", line 66, in execute
    return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)
  File "/home/rudrakshi/Desktop/Rose/assignment/env/lib/python3.8/site-packages/django/db/backends/utils.py", line 75, in _execute_with_wrappers
    return executor(sql, params, many, context)
  File "/home/rudrakshi/Desktop/Rose/assignment/env/lib/python3.8/site-packages/django/db/backends/utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
  File "/home/rudrakshi/Desktop/Rose/assignment/env/lib/python3.8/site-packages/django/db/utils.py", line 90, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "/home/rudrakshi/Desktop/Rose/assignment/env/lib/python3.8/site-packages/django/db/backends/utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)

Exception Type: ProgrammingError at /api/product/
Exception Value: relation "product" does not exist
LINE 1: ...product"."created_at", "product"."updated_at" FROM "product"
                                                              ^

运行 makemigrations 然后迁移后，我运行我的服务器，当我到达端点时 - 'api/product/' 我收到这个错误 - 关系“product”不存在 LINE 1: ...product"."created_at", "product"."updated_at" FROM “产品”

Answer 1

看看您的迁移文件，您有 'managed': False,，这是什么意思？这意味着您不希望迁移系统管理此模型。这意味着运行 migrate 不会导致在数据库中创建相应的表。 除非您了解自己在做什么，否则不要编辑迁移文件！

删除您可能对迁移文件所做的任何更改，尤其是 'managed': False,，然后运行：

python manage.py migrate product zero --fake

这将导致 Django 将应用“产品”的所有迁移标记为未应用。这很好，因为这似乎是您的初始迁移，否则您可能希望将 zero 更改为某个迁移名称。下一次运行：

python manage.py migrate

编程错误：SELECT COUNT(*) AS "__count" FROM "product"

1 个答案: