Python - Cloudant Get Changes

Question

I'm using the library Cloudant in order to gather documents from a Cloudant Database. Everytime I run the python script I get all the documents but I would like to retrieve only the documents added from the last execution of the script, in other words a get_changes function.

I have searched for an answer but it not seems to be easely to find.

Thaks for any help,

Filippo.

Answer 1

Use the changes() method. Keep track of the last sequence id, and restart from there to retrieve only the unseen changes.

# Iterate over a "normal" _changes feed
changes = db.changes()
for change in changes:
    print(change)

# ...time passes
new_changes = db.changes(since=changes.last_seq)
for new_change in new_changes:
    print(new_change)

If you also want the doc body, you can pass include_docs=True.

See https://github.com/cloudant/python-cloudant/blob/master/src/cloudant/database.py#L458

If you want to capture only new additions (as opposed to all changes), you can either create a filter function in a db design doc along the lines of:

function(doc, req) {
    // Skip deleted docs
    if (doc._deleted) {
        return false;
    }
    // Skip design docs
    if (doc._id.startsWith('_design')) {
        return false;
    }

    // Skip updates
    if (!doc._rev.startsWith('1-')) {
        return false;
    }

    return true;
}

and apply that to the changes feed:

new_changes = db.changes(since=changes.last_seq, filter='myddoc/myfilter'):
    # do stuff here

but probably as easy to simply get all the changes and filter in the Python code.

Filter functions: https://console.bluemix.net/docs/services/Cloudant/guides/replication_guide.html#filtered-replication