#14121: Provide object's primary key as a hint for database router method
db_for_read() when filtering objects by primary key
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Reporter: sa...@mahalo.com | Owner: nobody
Status: new | Milestone:
Component: Database layer (models, ORM) | Version: 1.2
Keywords: router, hints | Stage: Unreviewed
Has_patch: 0 |
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'''Problem:'''
Setting up a custom database router with db_for_read() method to allow for
sharding with MySQL. Need to be able to control what database an object is
read from on a per-object basis.
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'''Example Case:'''
I want to retrieve User objects from the database cluster as follows:
* If the username starts with a number, read from slave_db_1
* If the username starts with a letter, read from slave_db_2
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Currently, the only way to achieve this behavior is to specify "using" on
each condition, and per each call to the database.
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'''Proposed Solution:'''
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When filtering objects by primary key, pass the primary key to
db_for_read() as a hint.
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'''Example Code:'''
{{{
#View Code:
"""Assume username is pk for User model"""
users = User.objects.get(username="testuser")
#DB Router Code
class UserReadRouter(object):
def db_for_write(self, model, **hints):
return 'master'
def db_for_read(self, model, **hints):
"""Assume pk of User object is a string"""
if model.__name__ == "User" and 'object_pk' in hints:
if hints['object_pk'][0].isalpha():
return 'slave_db_2'
else:
return 'slave_db_1'
}}}
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The end result is that "testuser" is retrieved from slave_db_1.
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Ticket URL: <http://code.djangoproject.com/ticket/14121>
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