Google App Engine : alternate method of get_by_id()

By given an entity ID , I will query b开发者_JS百科y models = Model.get_by_id(id). However, I find out that some time it will not return result collectly.

Is there any alternative or recommended method to query by entity ID in Google App Engine, python?

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If you are saving your class instances with a parent then get_by_id will not return the object but instead will return None due to the reason that the key is not complete thus requiring the parent key as well. I encountered the same issue and was a pain in the ass to figure out.

ico = Icons.get_by_id("3", parent = parentkey)

This will return an object. ;-)

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If Model.get_by_id(id) returns None, this indicates that you've supplied an invalid ID, not that the method itself is unreliable.

It's not inconceivable that this method could fail in the event of a system outage, but if it did, your call would throw a datastore exception, not return an empty result.

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The problem disappear by itself after the 2011-05-10, which is the v1.5 launch date. Not sure this problem is related.

I didn't change any code, as the get_by_id() was fine all the while and on this few days. Beside, I added a cron job to run the get_by_id() every minutes and try to get the instance alive.

From my observation, the get_by_id() failed because it couldn't query the datastore.

Btw, the setting of datastore is Master/Slave Replication.

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get_by_id() always get the object, if the passed object is a valid id of object and if the objects exists in the datastore.

id can be got by object.key.id in the templat

else you always have the object.get(key).