how to filter the changes feed dynamically

[Alexander Gabriel]

in couchdb it is possible to filter a changes feed dynamically by passing an argument named request. See: http://docs.couchdb.org/en/latest/couchapp/ddocs.html#filter-functions. 

In this exaple a status can be passed:

GET /somedatabase/_changes?filter=mailbox/by_status&status=new HTTP/1.1

My use case: I want to filter only the users documents. So I need to pass the username.

I haven't found anything about this in the docs.

Is it possible?

[Nolan Lawson]

If you are trying to restrict users from reading each other's documents, you're probably going to want to go for the "db per user" approach (see the pouchdb-authentication readme). Another benefit is that you don't need filter functions.

In order to make your scenario work with filter functions, you would need to manually attach a username to every document stored in the database. And add a validate_doc_update function to ensure that users only write documents with their own username. A lot of headaches you can avoid by just doing "db per user" :).

[Alexander Gabriel]

It may well be that I am missing something but I believe a database per user is not the optimal solution for the app I'm working on.

Main reason: Users will be working together on projects and sharing lots of documents and attachments. Some of the attachments will be large (pixel basemaps for offline mapping). If 5 people work together in a project with a database per user that's five times the data on the server. And it's lots of syncing.

Plus rcouch'es view changes & view based replication are coming (soon?) in couchdb 2.0. I'm hoping couchdb 2.0 will be ready by the time my new app is ready (a few months). Otherwise I will use rcouch on the server (I develop on windows and rcouch doesn't run on windows).

This app is not going to have more than a few hundred or thousand users so I'm not bothered by the limitations of scaling filtered replication.

Yes, every document has a list of users which work with it.

So it would be nice if, until view changes & view based replication have arrived, I could filter the changes stream dynamically like in couchdb.

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[Nolan Lawson]

In that case, could you do a "role per group" model, where each user can have multiple roles, and each role has its own database?

As for view changes and view-based replication, such a thing may (eventually) exist in CouchDB, but it has not been implemented for PouchDB yet.

But if you really, really want filtered replication, then yes: you can do it in PouchDB/CouchDB. You just need to reference a design document that exists in CouchDB, exactly as you have it in your first message. The API does mention that "filter" is supported: http://pouchdb.com/api.html#changes

- Nolan

[Alexander Gabriel]

role per group, database per role?
sounds good
will give it a go
great help
thanks!

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[Alexander Gabriel]

nice, it works