django中的多个数据库支持

Question

From some forum I came to know that Multiple database support is added in Django at lower level, but the higher level apis are not added yet.

Can anyone please tell me how one can achieve multiple database connections in Django.

Does anyone have any idea by when Django will fully/officially support Multiple database connections.

Answer 1

If you simply need multiple connections, you can do something like this:

from django.db import load_backend
myBackend = load_backend('postgresql_psycopg2') # or 'mysql', 'sqlite3', 'oracle'
myConnection = myBackend.DatabaseWrapper({
    'DATABASE_HOST': '192.168.1.1',
    'DATABASE_NAME': 'my_database',
    'DATABASE_OPTIONS': {},
    'DATABASE_PASSWORD': "",
    'DATABASE_PORT': "",
    'DATABASE_USER': "my_user",
    'TIME_ZONE': "America/New_York",})
# Now we can do all the standard raw sql stuff with myConnection.
myCursor = myConnection.cursor()
myCursor.execute("SELECT COUNT(1) FROM my_table;")
myCursor.fetchone()

Answer 2

This will be in Django 1.2.

See http://docs.djangoproject.com/en/dev/topics/db/multi-db/

Answer 3

我在其上看到的最新讨论是在Proposal中：用于多数据库支持的用户友好API django-developers线程，其中还有一个使用原始消息中的Managers使用多个数据库的方法的示例。

Answer 4

If you read a few of the many ( many ) threads on this subject in django-dev, you will see that what looks straightforward, isn't. If you pick a single use case, then it looks easy, but as soon as you start to generalize in any way you start to run into trouble.

To use the above-referenced thread as an example, when you say "multiple databases", which of the following are you talking about?

• All DB on the same machine under the same engine.
• All DB on same machine, different engines (Eg MySQL + PostgreSQL)
• One Master DB with N read-only slaves on different machines.
• Sharding of tables across multiple DB servers.

Will you need:

• Foreign keys across DBs
• JOINs across machines and/or engines
• etc. etc.

One of the problems with a slick ORM like Django's is that it hides all of those messy details under a nice paint job. To continue to do that, but to then add in any of the above, is Not Easy (tm).

Answer 5

Eric Florenzano wrote a very good blog post that allows you some multiple database support at: Easy MultipleDatabase Support for Django .

It starts by creating a new custom manager that allows you to specify the database settings.

Answer 6

Multiple database to choose from

We always need one named default, the names of the rest are up to you.

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'mupltiple_datab_app1',                     
        'USER': 'root',                     
        'PASSWORD': 'admin',                  
        'HOST': "",                      
        'PORT': "",                     
    },
    'user1':{
        'ENGINE': 'django.db.backends.mysql', 
        'NAME': 'mupltiple_datab_app2',                      
        'USER': 'root',                     
        'PASSWORD': 'admin',                  
        'HOST': "",                        
        'PORT': "",  

    },
    'user2':{
        'ENGINE': 'django.db.backends.mysql', 
        'NAME': 'mupltiple_datab_app3',                      
        'USER': 'root',                     
        'PASSWORD': 'admin',                  
        'HOST':"" ,                     
        'PORT': "" ,  

    }
}

for sync to one particular database

manage.py syncdb --database=user1

Answer 7

There is a "using" directive for queries,saves, and deletes

https://docs.djangoproject.com/en/dev/topics/db/multi-db/#manually-selecting-a-database

Answer 8

Eric Florenzano's approach works well if all your databases use the same engine. If you have different engines (Postgres and MSSQL in my case) you will run into many issues deep in the ORM code (such as models/sql/where.py using the default connection's SQL syntax).

If you need this to work, you should wait for Alex Gaynor's MultiDB project which is planned for Django 1.2

Answer 9

From Django 1.2, it will support multiple databases. See: http://docs.djangoproject.com/en/dev/topics/db/multi-db/ Version 1.2 is now in beta

Answer 10

I think you will have to resort to "raw sql" .. kinda thing ..
look here: http://docs.djangoproject.com/en/dev/topics/db/sql/

you need a "connection" to your other database, if you look at django/db/__init__.py around line 39 (in my version ..)

connection = backend.DatabaseWrapper(**settings.DATABASE_OPTIONS)

try to take it from there ..
PS I haven't really tried this or anything .. just trying to point in the general direction of what I think might solve your problem.