Re: [google-appengine] Projection Queries does not work with order() and Limit parameter

[Alfred Fuller]

Does this happen in both the dev_appserver and production?

On Fri, Jun 15, 2012 at 10:28 AM, Christopher Ramírez <blindedb...@gmail.com> wrote:

I was trying to use projection queries, but I had extrange issues using them.

I'm trying to use them like this:

    offset_group = Clients.all( \

        projection=('name', 'sex', 'birth_date', 'email', 'discount')

    ).order('-__key__').fetch(limit=10, offset=skip_recs)

The above code is supposed to bring me the last 10 clients. But actually it does not return the last 10 (actually returns fewer and the actual last record is not included). Also the results seems alternated or maybe even/odd are skipped. If I take off projection param, the result is as spected:

offset_group = Clients.all().order('-__key__').fetch(limit=10, offset=skip_recs)

I do not know if this is a bug in projection queries or they have to be used in a different way. Please help me. I would like to use projection queries because they are really fast!

Kind Regards,

Christopher Ramírez

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[Christopher Ramírez]

Yes it happens on both servers.

On Monday, June 18, 2012 11:01:08 AM UTC-6, Alfred Fuller wrote:

Does this happen in both the dev_appserver and production?

On Fri, Jun 15, 2012 at 10:28 AM, Christopher Ramírez <blindedb...@gmail.com> wrote:

I was trying to use projection queries, but I had extrange issues using them.

I'm trying to use them like this:

    offset_group = Clients.all( \

        projection=('name', 'sex', 'birth_date', 'email', 'discount')

    ).order('-__key__').fetch(limit=10, offset=skip_recs)

The above code is supposed to bring me the last 10 clients. But actually it does not return the last 10 (actually returns fewer and the actual last record is not included). Also the results seems alternated or maybe even/odd are skipped. If I take off projection param, the result is as spected:

offset_group = Clients.all().order('-__key__').fetch(limit=10, offset=skip_recs)

I do not know if this is a bug in projection queries or they have to be used in a different way. Please help me. I would like to use projection queries because they are really fast!

Kind Regards,

Christopher Ramírez

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[timh]

I haven't used projections in queries, but I was just reading the docs and noted the following about indexes.

projection

List or tuple of names of properties to return. Only entities possessing the specified properties will be returned. If not specified, entire entities are returned by default. Projection queries are faster and cheaper than those that return complete entitites.

Note: Specifying this parameter may change the query's index requirements.

Maybe you have added the projection arg and are encountering an index that hasn't been rebuilt.  That could be one explanation. 

The other thing to check would be if the missing records have values for the properties specified in the projection.

Rgds

T

[Christopher Ramírez]

Hello Tim!

I checked your the points.

  the missing records have values for the properties specified in the projection. 

Yes, they have. I just even updated them in the datastore admin (production) and still don't appear.

 an index that hasn't been rebuilt 

I ran appcfg.py update_indexed and the problem still persists.

Another problem is that I'm specifing a limit of 20 records, but the projection query return me only 10 records. Actually, total existing instances are 20

I just added a few more records. The new ones appear without trouble. Missing records seems to be the ones saved before the projection index was created.

[Alfred Fuller]

what's your app id?

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[timh]

 

I just added a few more records. The new ones appear without trouble. Missing records seems to be the ones saved before the projection index was created.

If you added a new index, then pre-existing items won't be in the index, unless it's rebuilt.  Did you add new properties when you added

the projection index ? 

[Christopher Ramírez]

No as I remember.

How can I rebuild an Index?

[Alfred Fuller]

App Engine handles index building for you. When you add a new index, it will re-index all entities.

However, it is possible to save entities with an 'unindexed' property, then change the model definition to save the same property but 'indexed.' In this case, the old entities will remain unindexed, while new entities will be indexed. The only way to fix this is to re-write the old entities (as switching the indexing of a property is a schema change, and the datastore does not manage your schema).

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[Christopher Ramírez]

Thanks Alfred! Nice answare.

Now that you point me "indexed" property, I remember I changed it for some fields included in the proyection. Some of them were not indexed before been in the proyection. So, that coud be the issue.

On Wednesday, June 20, 2012 10:30:35 AM UTC-6, Alfred Fuller wrote:

App Engine handles index building for you. When you add a new index, it will re-index all entities.

However, it is possible to save entities with an 'unindexed' property, then change the model definition to save the same property but 'indexed.' In this case, the old entities will remain unindexed, while new entities will be indexed. The only way to fix this is to re-write the old entities (as switching the indexing of a property is a schema change, and the datastore does not manage your schema).

On Wed, Jun 20, 2012 at 8:37 AM, Christopher Ramírez <blindedb...@gmail.com> wrote:

No as I remember.

How can I rebuild an Index?

On Wednesday, June 20, 2012 2:53:12 AM UTC-6, timh wrote:

 

I just added a few more records. The new ones appear without trouble. Missing records seems to be the ones saved before the projection index was created.

If you added a new index, then pre-existing items won't be in the index, unless it's rebuilt.  Did you add new properties when you added

the projection index ? 

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