Will we be able to construct our own cursors much the same way that we are
able to construct our own Datastore keys (Key.from_path())?
Also along the same lines, will we be able to "deconstruct" a cursor to get
its components (offset, start_inclusive etc.), as we can now do with keys (
key.name(), key.id(), key.kind() etc.)?
2010/2/9 Nick Johnson (Google) <nick.john...@google.com>
> 2010/2/9 Stephen <sdea...@gmail.com>
>
>
>> I'm asking if it's wise to store it as a query parameter embedded in a
>> web page.
>>
>
> You're right that it's unwise. Depending on how you construct your query, a
> user could potentially modify the cursor they send to you to return results
> from any query your datastore is capable of performing, which could result
> in you revealing information to the user that they shouldn't know. You
> should either store the cursor on the server-side, or encrypt it before
> sending it to the client.
>
> I was going to mention something about this in my post, but it slipped my
> mind.
>
> -Nick Johnson
>
>>
>>
>> On Feb 9, 12:26 am, "Ikai L (Google)" <ika...@google.com> wrote:
>> > A cursor serializes to a Base64 encoded String, so you can store it
>> anywhere
>> > you want to store strings: Memcached, Datastore, etc. You can even pass
>> it
>> > as an URL parameter to task queues.
>> >
>> > 2010/2/8 Stephen <sdea...@gmail.com>
>> >
>> >
>> >
>> >
>> >
>> > > Ah right, Nick's blog does say start_key and not offset. My bad.
>> >
>> > > Maybe there will be warnings in the upcoming documentation, but my
>> > > first instinct was to embed the serialised cursor in the HTML as the
>> > > 'next' link. But that doesn't look like a good idea as Nick's decoded
>> > > query shows what's embedded:
>> >
>> > > PrimaryScan {
>> > > start_key: "shell\000TestModel\000foo\000\232bar\000\200"
>> > > start_inclusive: true
>> > > }
>> > > keys_only: false
>> >
>> > > First, you may or may not want to leak this info. Second, could this
>> > > be altered on the client to change the query in any way that's
>> > > undesirable?
>> >
>> > > Once you have a cursor, where do you store it so you can use it again?
>> >
>> > > On Feb 8, 10:17 pm, "Ikai L (Google)" <ika...@google.com> wrote:
>> > > > I got beaten to this answer. No, there is no traversal to get to the
>> > > offset.
>> >
>> > > > BigTable has an underlying mechanism for range queries on keys.
>> Indexes
>> > > are
>> > > > essentially a key comprised of a concatenation of application ID,
>> entity
>> > > > type, column, value. When a filter operation is performed, the
>> datastore
>> > > > looks for a range matching this criteria, returning the set of keys.
>> A
>> > > > cursor also adds the datastore key of the entity so it is possible
>> to
>> > > > serialize where to begin the query. This is actually a bit awkward
>> to
>> > > > explain without visuals. You can watch Ryan Barrett's talk here:
>> >
>> > > >http://www.youtube.com/watch?v=tx5gdoNpcZM
>> >
>> > > > Hopefully, we'll be able to post an article at some point in the
>> future
>> > > > explaining how cursors work.
>> >
>> > > > 2010/2/8 Alkis Evlogimenos ('Αλκης Ευλογημένος) <
>> evlogime...@gmail.com>
>> >
>> > > > > There is no offset. The protocol buffer stores a start_key and a
>> > > boolean
>> > > > > denoting if this start key is inclusive or not. The performance of
>> > > > > continuing the fetch from a cursor should be the same as the
>> > > performance of
>> > > > > the first entities you got from a query.
>> >
>> > > > > On Mon, Feb 8, 2010 at 4:33 PM, Stephen <sdea...@gmail.com>
>> wrote:
>> >
>> > > > >> On Feb 8, 7:06 pm, "Ikai L (Google)" <ika...@google.com> wrote:
>> > > > >> > The official docs are pending, but here's Nick Johnson to the
>> > > rescue:
>> >
>> > >
>> http://blog.notdot.net/2010/02/New-features-in-1-3-1-prerelease-Cursors
>> >
>> > > > >> What are the performance characteristics of cursors?
>> >
>> > > > >> The serialised cursor shows that it stores an offset. Does that
>> mean
>> > > > >> that if the offset is one million, one million rows will have to
>> be
>> > > > >> skipped before the next 10 are returned? This will be faster than
>> > > > >> doing it in your app, but not as quick as the existing bookmark
>> > > > >> techniques which use the primary key index.
>> >
>> > > > >> Or is the server-side stateful, like a typical SQL implementation
>> of
>> > > > >> cursors? In which case, are there any limits to the number of
>> active
>> > > > >> cursors? Or what if a cursor is resumed some time in the future;
>> will
>> > > > >> it work at all, or work slower?
>> >
>> > > > >> --
>> > > > >> You received this message because you are subscribed to the
>> Google
>> > > Groups
>> > > > >> "Google App Engine" group.
>> > > > >> To post to this group, send email to
>> > > google-appeng...@googlegroups.com.
>> > > > >> To unsubscribe from this group, send email to
>> > > > >> google-appengine+unsubscr...@googlegroups.com<google-appengine%2bunsubscr...@googlegroups.com>
>> <google-appengine%2bunsubscr...@googlegroups.com<google-appengine%252bunsubscr...@googlegroups.com>
>> >
>> > > <google-appengine%2bunsubscr...@googlegroups.com<google-appengine%252bunsubscr...@googlegroups.com>
>> <google-appengine%252bunsubscr...@googlegroups.com<google-appengine%25252bunsubscr...@googlegroups.com>
>> >
>> >
>> > > > >> .
>> > > > >> For more options, visit this group at
>> > > > >>http://groups.google.com/group/google-appengine?hl=en.
>> >
>> > > > > --
>> >
>> > > > > Alkis
>> >
>> > > > > --
>> > > > > You received this message because you are subscribed to the Google
>> > > Groups
>> > > > > "Google App Engine" group.
>> > > > > To post to this group, send email to
>> google-appengine@googlegroups.com
>> > > .
>> > > > > To unsubscribe from this group, send email to
>> > > > > google-appengine+unsubscr...@googlegroups.com<google-appengine%2bunsubscr...@googlegroups.com>
>> <google-appengine%2bunsubscr...@googlegroups.com<google-appengine%252bunsubscr...@googlegroups.com>
>> >
>> > > <google-appengine%2bunsubscr...@googlegroups.com<google-appengine%252bunsubscr...@googlegroups.com>
>> <google-appengine%252bunsubscr...@googlegroups.com<google-appengine%25252bunsubscr...@googlegroups.com>
>> >
>> >
>> > > > > .
>> > > > > For more options, visit this group at
>> > > > >http://groups.google.com/group/google-appengine?hl=en.
>> >
>> > > > --
>> > > > Ikai Lan
>> > > > Developer Programs Engineer, Google App Enginehttp://
>> > > googleappengine.blogspot.com|http://twitter.com/app_engine
>> >
>> > > --
>> > > You received this message because you are subscribed to the Google
>> Groups
>> > > "Google App Engine" group.
>> > > To post to this group, send email to
>> google-appeng...@googlegroups.com.
>> > > To unsubscribe from this group, send email to
>> > > google-appengine+unsubscr...@googlegroups.com<google-appengine%2bunsubscr...@googlegroups.com>
>> <google-appengine%2bunsubscr...@googlegroups.com<google-appengine%252bunsubscr...@googlegroups.com>
>> >
>> > > .
>> > > For more options, visit this group at
>> > >http://groups.google.com/group/google-appengine?hl=en.
>> >
>> > --
>> > Ikai Lan
>> > Developer Programs Engineer, Google App Enginehttp://
>> googleappengine.blogspot.com|http://twitter.com/app_engine
>>
>> --
>> You received this message because you are subscribed to the Google Groups
>> "Google App Engine" group.
>> To post to this group, send email to google-appeng...@googlegroups.com.
>> To unsubscribe from this group, send email to
>> google-appengine+unsubscr...@googlegroups.com<google-appengine%2bunsubscr...@googlegroups.com>
>> .
>> For more options, visit this group at
>> http://groups.google.com/group/google-appengine?hl=en.
>>
>>
>
>
> --
> Nick Johnson, Developer Programs Engineer, App Engine
> Google Ireland Ltd. :: Registered in Dublin, Ireland, Registration Number:
> 368047
>
> --
> You received this message because you are subscribed to the Google Groups
> "Google App Engine" group.
> To post to this group, send email to google-appeng...@googlegroups.com.
> To unsubscribe from this group, send email to
> google-appengine+unsubscr...@googlegroups.com<google-appengine%2bunsubscr...@googlegroups.com>
> .
> For more options, visit this group at
> http://groups.google.com/group/google-appengine?hl=en.
>
--
You received this message because you are subscribed to the Google Groups
"Google App Engine" group.
To post to this group, send email to google-appeng...@googlegroups.com.
To unsubscribe from this group, send email to
google-appengine+unsubscr...@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/google-appengine?hl=en.
