Add cache_prefix setting (fixes #227)

[lavish205]

issue #227

[lavish205]

@leplatrem I'm getting cache_prefix KeyError as config.get_settings() is not returning settings defined in DEFAULT_SETTINGS

[leplatrem]

It looks perfectly correct.

But when test are ran:

$ nosetests -s cliquet.tests.test_cache

I also get this error:

Traceback (most recent call last):
  File "/home/mathieu/Code/Mozilla/cliquet/cliquet/tests/test_cache.py", line 40, in setUp
    self.cache = self.backend.load_from_config(self._get_config())
  File "/home/mathieu/Code/Mozilla/cliquet/cliquet/cache/memory.py", line 55, in load_from_config
    prefix = settings['cache_prefix']
KeyError: 'cache_prefix'

That's because the tests setup do not use DEFAULT_SETTINGS.
See, you should add something like this on MemoryCacheTest https://github.com/mozilla-services/cliquet/blob/master/cliquet/tests/test_cache.py#L162-L165

[lavish205]

@leplatrem I have fixed this KeyError by .get() method, hope this works

[leplatrem]

hope this works.

Nope actually. You should leave ['cache_prefix'] and set its value in the tests like I pointed out.

Here is a small list of things to do before this could be merged:

• Generalize the change to other backends (redis and postgresql)
• Add some tests in test_cache.py to ensure that the prefix value is used to get the data associated to a key
• Add some tests in test_cache.py to ensure that the prefix value is used to set the data associated to a key
• Add some tests in test_cache.py to ensure that the prefix value is used to delete the data associated to a key
• Add some tests in test_cache.py to ensure that the prefix value is used to ttl the data associated to a key
• Add some tests in test_cache.py to ensure that the prefix value is used to expire the data associated to a key
• Add a test to ensure that the default prefix value is empty
• Update configuration documentation
• Update changelog
• Add yourself to contributors

[leplatrem]

@lavish205 you could do something like that (I didn't test it):

def test_get_uses_prefix(self):
    settings_prefix = self.settings.copy()
    settings_prefix['cache_prefix'] = 'prefix_'
    config_prefix = self._get_config(settings=settings_prefix)

    # Instantiate a cache backend with a prefix:
    backend_prefix = self.backend.load_from_config(config_prefix)

    # Set a value with a cache that has no prefix:
    self.cache.set('prefix_key', 'foo')

    # Obtain the value with the cache that has a prefix:
    obtained = backend_prefix.get('key')
    self.assertEqual(obtained, 'foo')

[lavish205]

@leplatrem I think something is wrong with the code as test cases are not working as expected.

[leplatrem]

@lavish205 yes, first you shouldn't set the prefix to 123, so both self.cache and backend_prefix have a prefix.

Then, in order to make tests pass, you should use the self.prefix in def get() in the Cache backend class.

[lavish205]

@leplatrem value of backend_prefix is {'prefix': 'prefix_', '_store': {'prefix_key': 'bar'}, '_ttl': {}, so can't access prefix_key on root of dict.

[leplatrem]

This should be get('key') since this backend has prefix prefix_ !

[lavish205]

@leplatrem can you please check, if there is need to add more test cases?

[Natim]

I would rather use format here: key = "{}{}".format(self.prefix, key) or key = "%s%s" % (self.prefix, key)

[leplatrem]

Why ?

[Natim]

That's a great job @lavish205 👍 Thank you for working on it :)

[lavish205]

@leplatrem what to update in configuration documentation?

[Natim]

@lavish205 I believe it is just about adding the cache_prefix configuration settings as you told me on IRC.

13:52:43 <lavish_> do I need to add prefix changes here?
http://kinto.readthedocs.org/en/latest/configuration/settings.html#cache

[lavish205]

@Natim what exactly I have write under "What does it do?" column ?

[Natim]

@lavish205 Something like: It adds a prefix to cache key names so that multiple kinto server can use the same cache database without disturbing each other.

[leplatrem]

The setting is called cache_prefix no?

[Natim]

I have added some documentation and a test to make sure cache.get added the prefix.

Thank you @lavish205 for your work on this.

[leplatrem]

Congrats @lavish205 for keeping the faith and going through all this!

Thank you for getting involved with patience !

[lavish205]

Thanks to both of you @leplatrem @Natim :)