Google-app-engine – How to query in GQL using the entity key

google-app-enginegoogle-cloud-datastoregql

How do I write a query against the entity key using GQL in the Google App Engine Data Viewer ?

In the viewer, the first column (Id/Name) displays as name=_1, in the detail view it shows the key as

Decoded entity key: Programme: name=_1
Entity key: agtzcG9...................

This query does not work:

SELECT * FROM Programme where name = '_1'

Best Answer

You can use the entity's key to retrieve it:

SELECT * FROM Programme where __key__ = KEY('agtzcG9...................')

And, you should be able to query using the name similarly:

SELECT * FROM Programme where __key__ = KEY(Programme, '_1')

Note that this is not something that you would want to do in your AppEngine application; as Nick notes in his comment, it is a huge waste of time. Really, this example is only good to show you how to query by Key in the Admin console.

Related Solutions

Go – GQL query to effectively span entity relationships

You're right, the App Engine datastore doesn't allow for this sort of query. And you're right that the list comprehension is inefficient. Consider, though, that that is pretty much exactly what a relational database does when you execute a query with joins like your one - the database has to perform the same O(n^3) work you're doing here - the only difference is that you're doing it in Python, and with additional round trip time. Since App Engine is designed to scale, it's not really made for these sort of queries.

Usually, though, there's a way you can denormalise your model a bit to facilitate this, by moving some of the properties you need to access onto the Foo model, or if you are doing aggregates, by moving the total onto the Foo model. It's difficult to give concrete solutions without more of an idea of what problem you're trying to solve, though.

Python – Filtering by entity key name in Google App Engine on Python

from google.appengine.api.datastore import Key
query.filter("__key__ >=", Key.from_path('User', 'abc'))

Best Answer

Related Solutions

Go – GQL query to effectively span entity relationships

Python – Filtering by entity key name in Google App Engine on Python

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