Filter query by key name

[S.Prymak]

I have to query datastore for entities with key names which are greater or equals to specified string. Something like this:

def get_pages_by_key_name(key):
  p = models.Page(key_name=key)
  query = GqlQuery("SELECT * FROM Page WHERE ???? :1", p.key.name())

  return [i for i in query]

How can I do that?

[Joseph Letness]

Hi, the model class already has a built in function for retrieving an
entity by key name:

my_entity = MyModel.get_by_key_name(key_name)

Also, key names are unique within a data model. Your example shows an
iteration over multiple entities which will never happen if you are
querying on a key name.

Hope this helps.

--Joe

[S.Prymak]

Thank you for reply, Joseph.

I know about get_by_key_name. Now I see that my example is not correct.

I need all entites wich key().name() is greater or equal to specified string. May be my example query should be GqlQuery("SELECT * FROM Page WHERE __key__.name >= :1", p.key.name()) which is not a correct query in current implementation of GAE. Comparing keys like "__key__ >= :1" does not work for me.

[S.Prymak]

Here is why comparing key does not work:

import models

pk=models.Page(key_name='_blocks')

q=models.Page.gql("WHERE __key__ >= :1", pk.key())

[p.key().name() for p in q]

[u'_blocks--callout', u'_blocks--callout-contact', u'_blocks--footer-center', u'_blocks--teaser', u'_slides--home--1', u'about', u'collections', u'default', u'faq', u'shipping']

In my implementation key name is a "slug" for page. I want only those pages wich slug begins with '_blocks'. Is it possible quering by key name?

I thought about [p for p in models.Page.all() if p.key().name() >= '_blocks'], but I doubt it has good perfomance on large set of entities.

[Mark Bucciarelli]

i don't think you can do what you want.

in gql condition, you only have access to

__key__, which i bet is some hash of

kind + keyname + ...

so, keys_only query, then scan results.

or add another string prop and then

use some trick like 

  q.filter('key_s >=', u'_block\u0000')

  q.filter('key_s <=', u'_block\u9999)

m

--
You received this message because you are subscribed to the Google Groups "Google App Engine" group.

To view this discussion on the web visit https://groups.google.com/d/msg/google-appengine/-/Z8h6AQSoQw4J.

To post to this group, send email to google-a...@googlegroups.com.
To unsubscribe from this group, send email to google-appengi...@googlegroups.com.
For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.

[Stephen Johnson]

You definitely can do queries by your keys. I'm not a Python person but it looks to me like your problem is that you've forgotten the <= part of the query so you get the _slides objects because _slides is > _blocks. You also get faq, default, shipping etc. because the underscore character is less than in Unicode (and thus ASCII) than the lower case letters. So try adding: __key++ <= :2 where :2 is a key equal to '_blocks' + \uFFFD'

Stephen

www.cortexconnect.com

--

You received this message because you are subscribed to the Google Groups "Google App Engine" group.

[Stephen Johnson]

I meant __key__ not __key.

[Stephen Johnson]

I meant _key__ not __key++. Damn fingers.

[S.Prymak]

Thank you, Stephen! You are totally right!

That's solved my problem!  That was my stupid, stupid assumption about string comparision algoritm :(

[Stephen Johnson]

Your welcome. Glad to be of help!

On Tue, Aug 30, 2011 at 3:20 PM, S.Prymak <spr...@gmail.com> wrote:

Thank you, Stephen! You are totally right!

That's solved my problem!  That was my stupid, stupid assumption about string comparision algoritm :(

--
You received this message because you are subscribed to the Google Groups "Google App Engine" group.

To view this discussion on the web visit https://groups.google.com/d/msg/google-appengine/-/EdaT7weIv_8J.