服务器启动后Django多个动态数据库 [英] Django multiple dynamic databases after server startup
问题描述
我是django的新手，并尝试找出对我而言在django中动态使用多个数据库的最佳解决方案。
我知道django可以使用settings.py文件中注册的多个数据库，但就我而言，我有一个主数据库（sqlite）作为我的存储库，我创建了所有模型，其余的api视图集
I'm new to django and try to figure out what would be the best solution for me to use dynamically multiple databases in django. I know django is able to work with multiple databases registered in the settings.py file but In my case I have one main database (sqlite) which acts as my repository, I created all the models, the rest api viewsets for this one.
用户可以通过输入连接信息来选择连接到Oracle数据库，然后我需要从该数据库收集数据并将其插入到我的存储库中。用户可以通过该应用程序注册多个Oracle数据库。我想知道是否应该使用纯cx_Oracle类来处理来自Django的那些连接，还是应该在settings.py中注册它们？
The user can choose to connect to an Oracle database by entering the connection information and then I will need to gather data from this database and insert it to my repository. The user can register multiple Oracle databases through the app. I'm wondering if I should use a pure cx_Oracle class to handle those connection from django or if I should register them in the settings.py?
前端中的每个视图都映射到特定的数据库，我将需要在它们之间切换上下文，如果使用cx_Oracle类，如何将请求路由到右侧后端中的类实例？
Each view in the frontend maps to a specific database and I will need to switch context between them, If I use a cx_Oracle class how can I route the requests to the right class instance in the backend?
任何帮助或见识都会受到赞赏，我在互联网上找不到与我的用例匹配的东西。
Any help or insight would be appreciated, I didn't find anything matching my use case on the internet.
推荐答案
在注释中找到-此处是一篇文章，描述了如何通过动态选择数据库来设置服务器实例，因此其作者是应该获得所有荣誉的人。重述基本方法：
As found out in the comments - here is an article describing how to set up a server instance with selecting databases on the fly, so its author is the one that should get all credits. Restating the basic approach:
-
创建代表数据库连接的模型类：
Create a model class representing the db connection:
class Database(models.Model):
name = models.CharField(max_length=256, unique=True)
config = JSONField()
添加 label 属性以区分db连接实体。在这里，它需要在django设置中设置字符串 DYNAMIC_DATABASES_PREFIX 和 DYNAMIC_DATABASES_SEPARATOR ，但也可以将其硬编码为一些常量：
Add a label property to distinct the db connection entities. Here, it requires to set strings DYNAMIC_DATABASES_PREFIX and DYNAMIC_DATABASES_SEPARATOR in the django settings, but could also be hardcoded as some constants:
class Database(models.Model):
...
@property
def label(self):
# We want to be able to identify the dynamic databases and apps
# So we prepend their names with a common string
prefix = getattr(settings, 'DYNAMIC_DATABASES_PREFIX', 'DYNAMIC_DATABASE')
separator = getattr(settings, 'DYNAMIC_DATABASES_SEPARATOR', '_')
return '{}{}{}'.format(prefix, separator, self.pk)
添加一种方法，用于将db连接添加到Django的db连接中/从db连接中删除db连接（精妙的部分正在为每个数据库连接放置一个虚拟应用程序-这样，我们可以拥有具有重复表名的不同数据库）：
Add a method for adding the db connection to/removing the db connection from django's db connections (the nifty part is putting a dummy app for each db connection - this way we can have different databases with duplicate table names):
class Database(models.Model):
...
def register(self):
# label for the database connection and dummy app
label = self.label
# Do we have this database registered yet
if label not in connections._databases:
# Register the database
connections._databases[label] = self.config
# Break the cached version of the database dict so it'll find our new database
del connections.databases
# Have we registered our fake app that'll hold the models for this database
if label not in apps.app_configs:
# We create our own AppConfig class, because the Django one needs a path to the module that is the app.
# Our dummy app obviously doesn't have a path
AppConfig2 = type('AppConfig'.encode('utf8'),(AppConfig,),
{'path': '/tmp/{}'.format(label)})
app_config = AppConfig2(label, label)
# Manually register the app with the running Django instance
apps.app_configs[label] = app_config
apps.app_configs[label].models = {}
def unregister(self):
label = self.label
if label in apps.app_configs:
del apps.app_configs[label]
if label in apps.all_models:
del apps.all_models[label]
if label in connections._databases:
del connections._databases[label]
del connections.databases
通过连接添加连接查找该名称还将注册与正在运行的django实例的连接，从而使其可操作：
Add a connection lookup by connection name that also registers the connection to running django instance, making it operational:
class Database(models.Model):
...
def get_model(self, table_name):
# Ensure the database connect and it's dummy app are registered
self.register()
label = self.label
model_name = table_name.lower().replace('_', '')
# Is the model already registered with the dummy app?
if model_name not in apps.all_models[label]:
# Use the "inspectdb" management command to get the structure of the table for us.
file_obj = StringIO()
Command(stdout=file_obj).handle(database=label, table_name_filter=lambda t: t == table_name)
model_definition = file_obj.getvalue()
file_obj.close()
# Make sure that we found the table and have a model definition
loc = model_definition.find('(models.Model):')
if loc != -1:
# Ensure that the Model has a primary key.
# Django doesn't support multiple column primary keys,
# So we have to add a primary key if the inspect command didn't
if model_definition.find('primary_key', loc) == -1:
loc = model_definition.find('(', loc + 14)
model_definition = '{}primary_key=True, {}'.format(model_definition[:loc + 1], model_definition[loc + 1:])
# Ensure that the model specifies what app_label it belongs to
loc = model_definition.find('db_table = \'{}\''.format(table_name))
if loc != -1:
model_definition = '{}app_label = \'{}\'\n {}'.format(model_definition[:loc], label, model_definition[loc:])
# Register the model with Django. Sad day when we use 'exec'
exec(model_definition, globals(), locals())
# Update the list of models that the app
# has to match what Django now has for this app
apps.app_configs[label].models = apps.all_models[label]
else:
logger.info('Could not find table: %s %s', label, table_name)
else:
logger.info('Already added dynamic model: %s %s', label, table_name)
# If we have the connection, app and model. Return the model class
if (label in connections._databases and label in apps.all_models and model_name in apps.all_models[label]):
return apps.get_model(label, model_name)
使用提到的配置字符串选择数据库来创建自定义数据库路由：
Create custom db routing, using the mentioned config strings for db selection:
class DynamicDatabasesRouter(object):
label_prefix = '{}{}'.format(
getattr(settings, 'DYNAMIC_DATABASES_PREFIX', 'DYNAMIC_DATABASE'),
getattr(settings, 'DYNAMIC_DATABASES_SEPARATOR', '_')
)
def db_for_read(self, model, **hints):
if model._meta.app_label.startswith(self.label_prefix):
# We know that our app_label matches the database connection's name
return model._meta.app_label
return None
def db_for_write(self, model, **hints):
if model._meta.app_label.startswith(self.label_prefix):
# We know that our app_label matches the database connection's name
return model._meta.app_label
return None
def allow_relation(self, obj1, obj2, **hints):
return None
def allow_migrate(self, db, app_label, model_name=None, **hints):
return None
在设置中注册路由器：
Register the router in settings:
DATABASE_ROUTERS = ['myapp.routing.DynamicDatabasesRouter']
（可选）使模型可在管理网站（如果使用它）：
(Optional) make the model modifiable in the admin site if you use it:
def config(conn):
return json.dumps(conn.config)
config.short_description = 'Config'
class DatabaseAdmin(admin.ModelAdmin):
list_display = ('name', config)
admin.site.register(Database, DatabaseAdmin)
视图中的示例用法：
class HomeView(TemplateView):
template_name = 'home.html'
def get_context_data(self):
context = super(HomeView, self).get_context_data()
# We can pick which dynamic database connection we want based on a GET parameter
db = Database.objects.get(pk=self.request.GET.get('env', 1))
# Pass the database instance to the template so we can display it.
context['db'] = db
# Get a model class for a table in our dynamic database.
# Lets pretend there's a table called 'author'
Author = db.get_model('author')
authors = Author.objects.all().order_by('name')
# Send the author instances to the template for iterating over.
context['authors'] = authors
return context
这篇关于服务器启动后Django多个动态数据库的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
