I ended up with this:
class ReadOnlyError(db.Error):
pass
def make_datastore_readonly():
"""Throw ReadOnlyError on put and delete operations."""
def hook(service, call, request, response):
assert(service == 'datastore_v3')
if users.is_current_user_admin():
return
if call in ('Put', 'Delete'):
raise ReadOnlyError('Datastore is in read-only mode')
apiproxy_stub_map.apiproxy.GetPreCallHooks().Push(
'readonly_datastore', hook, 'datastore_v3')
And special cased the ReadOnlyError exception in the read handler to print
out an error (503) that shows the site is on read only mode. Then I did the
migration, everything went fine :-)
2009/5/1 Jason (Google) <apija...@google.com>
> I second djidjadji's suggestion. While it's true that your application
> will be unavailable, it's definitely the simplest solution and gives your
> users a clear expectation that some of your application's functionality is
> not available; otherwise, they might be confused why some aspects of your
> site work but others don't, especially if your messaging is subtle.
>
> The only other suggestion is to wrap all of your write calls to the
> datastore so you can easily disable them altogether. That's tricker than the
> first solution, however.
>
> - Jason
>
>
> 2009/4/28 Alkis Evlogimenos ('Αλκης Ευλογημένος) <evlogime...@gmail.com>
>
>> Yes but this means no access to the site for the duration. I want to have
>> read only access to the site for the duration.
>>
>> 2009/4/28 djidjadji <djidja...@gmail.com>
>>
>>
>>> If you don't have to do it often you can use the following method.
>>>
>>> Make a version of the application that displays a page that the site
>>> is temporarily under maintenance. Give an estimate for how long it
>>> will take.
>>> app.yaml redirects all requests to maintenance.py
>>>
>>> Find a time of day where the site is less busy.
>>> Make the maintenance version current.
>>> Update version X to the new schema.
>>> Do the update using urls http://X.latest.myapp.appspot.com
>>> Test the update
>>> Make X the new version.
>>>
>>> This is the least hassle, I think.
>>>
>>> 2009/4/28 Alkis Evlogimenos ('Αλκης Ευλογημένος) <evlogime...@gmail.com
>>> >:
>>> > Sometimes you want to make the datastore readonly for users to perform
>>> some
>>> > global changes (say schema update).
>>> > How do people achieve this?
>>> > Out of what I can think of:
>>> > - Do you write another version of your application that errors on each
>>> > request that writes to the datastore? This seems error prone and a
>>> > maintenance headache.
>>> > - Do you monkeypatch db.put and db.delete to unconditionally throw an
>>> > exception and make that exception visible to the frontend?
>>> > - Do you use hooks and pre hook datastore operations to throw an
>>> exception
>>> > and make that exception visible to the frontend?
>>> > Any other ideas?
>>> > --
>>> >
>>> > Alkis
>>>
>>>
>>>
>>
>>
>> --
>>
>> Alkis
>>
>>
>>
>
> >
>
--
Alkis
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