烧瓶MongoEngine - 如何更改数据库？ [英] Flask MongoEngine - How to change database?

问题描述

我有一个Flags应用程序，其中包含一个 Post 模型，它跨越多个MongoDB数据库（db1，db2，db3，...），所以我需要能够查询不同的dbs。

我使用 Flask-MongoEngine 扩展名。
$ b

我的 __ init __。py 包含以下行：

db = MongoEngine（app）

和 config.py 我有：

MONGODB_SETTINGS = {'DB'：'db1'}

$ ol

改变 db 对象中的连接参数像这样：

db.connection = mongoengine.connect（'db2'）

它没有改变任何东西。执行 post = Post.objects.all（）仍然运行在原始数据库（ db1 ）上。

在 Post class meta 中创建别名，如下所示：

'db_alias'：'db1'

然后我改变了连接参数在这样的 db 对象中：

db.connection = mongoengine.connect（'db2'，alias ='db1' ）

这确实会创建一个连接到 db2 ，但是我无法更改它到另一个分贝。

将 MONGODB_SETTINGS 设置为 {'DB'：'db2'} 和那么 db = MongoEngine（app）

这也行不通

好像一旦 models.py 中的模型已经被加载（或者连接到一个db），你就不能改变它的连接。
是否正确？

如何在同一个模型上更改数据库？

编辑：Django等价于使用参数，它允许查询不同的数据库的相同模型。

解决方案

> MongoEngine 实例，因此从它创建的所有文档（模型）都被绑定到一个特定的数据库。



您可以（暂时）通过调用实例中的 switch_db 方法，将一个文档实例添加到文档类中定义的别名中：



  Post.obje保存（）
  

将保存所有文档数据库 db1 if db1 定义为 db_alias Post 类（否则你会得到一个 ConnectionError ）。 b
$ b

或者有很多方法可以使初始配置成为动态，例如尊重环境变量：

pre $ import $ $ b $ app ['MONGODB_SETTINGS'] = {'db'：os.environ。 get（'DBNAME'，'db2'）}


然而，从您的评论

我们的系统使用多个数据库来托管这个模型

看起来你可能需要的是 Sharding ，MongoDB负责分发集合多个机器上有多个 mongod 个实例。在这种情况下，你可以连接到一个 mongos ，它负责将查询路由到右边的分片。数据库名称在每个分片上都是相同的。

I have Flask app with a Post model which spans across multiple MongoDB databases (db1, db2, db3,...), so I need to be able to query different dbs.
I'm using Flask-MongoEngine extension.

My __init__.py contains the following line:
db = MongoEngine(app)
and in config.py I have:
MONGODB_SETTINGS = {'DB': 'db1'}

I tried the following without success:

1. Alter the connection parameter in the db object like this:
   db.connection = mongoengine.connect('db2')
   It didn't change anything. Executing post = Post.objects.all() still ran on the original db (db1).
2. Create alias in the Post class meta like this:
   'db_alias': 'db1'
   Then I altered the connection parameter in the db object like this:
   db.connection = mongoengine.connect('db2', alias='db1')
   This would indeed create a connection to db2, but I couldn't change it to another db.
3. Set MONGODB_SETTINGS to {'DB': 'db2'} and then db = MongoEngine(app)
   This doesn't work as well

It seems like once the model in models.py has been loaded (or connected to a db), you cannot change its connection.
Is that correct?
How can I change databases on the same model?
EDIT: The Django equivalent is the using parameter in the ORM which allows querying different DBs for the same model.

解决方案

As you correctly identified, a MongoEngine instance and consequently all the documents (models) created from it are bound to a particular database.

You can (temporarily) change the database used by a document instance to an alias defined in the document's class by calling the switch_db method on the instance:

Post.objects.all().switch('db1').save()

would save all documents in the database db1 if db1 was defined as db_alias in the Post class (otherwise you'll get a ConnectionError).

Alternatively there are a number of ways to make the initial configuration "dynamic" and e.g. respect environment variables:

import os
app['MONGODB_SETTINGS'] = {'db': os.environ.get('DBNAME', 'db2')}

However, from your comment

Our system uses a number of databases to host this model

it seems that what you probably want is Sharding, where MongoDB takes care of distributing a collection over multiple mongod instances on multiple machines. In that case you connect to a mongos instead, which takes care of routing a query to the right shard. The database name is the same on each shard.

这篇关于烧瓶MongoEngine - 如何更改数据库？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！