Support multiple types of composite filters

[pcostell]

Right now Datastore doesn't natively support OR filters, however it is a feature we'd like to support. When switching from GAE Datastore to Cloud Datastore filters were explicitly changed from being represented as a list to a more hierarchical model to support this. There should be a plan in place for how to expose this, since now filters are assumed to be AND'ed together.

[tseaver]

The generated 'datastore_v1_pb2' protobuf module doesn't have any other values than 'AND' for the 'CompositeFilter.Operator' enum type:

https://github.com/GoogleCloudPlatform/gcloud-python/blob/58f08fa3826ad52a3318e9d375f66917efced36b/setup.py#L18

nor does the upstream protobuf spec:

https://github.com/GoogleCloudPlatform/google-cloud-datastore/blob/6073e01540264db58ee50c30a1e9f006677eb794/proto/datastore_v1.proto#L286

Wouldn't we need the server-side folks to update the API to support such filters before we could do anything about it in the Python wrapper?

[pcostell]

Yes the server doesn't currently support anything besides AND. However as is the API has all filters listed sequentially q.filter('a =', 1).filter('b =', 2). Once other filters are implemented server-side, this API will have to be deprecated in order to support different types of filters.

[tseaver]

@silvolu, given that we can't implement this until the server API spec is updated, should the be an M1 issue?

[silvolu]

No, I'm actually closing this issue. I added to M1 because I wanted to think about if we wanted to change something in the current design before releasing M1, but I think that deprecating if needed will be fine.