paginator.py

from app import app
from flask import jsonify, Flask
from google.appengine.ext import ndb
from google.appengine.ext.ndb import metadata
from google.appengine.datastore.datastore_query import Cursor


app = Flask(__name__)

def paginate(kind, urlsafe_cursor=None):
    """
    Starts (or continues) pagination of keys in the datastore

    RESPONSE Body (as JSON)
    {
    cursor: CURSOR,
    keys: [URLSAFE_KEY_1, URLSAFE_KEY_2, ..., URLSAFE_KEY_N]
    }

    WHERE:
    CURSOR - A opaque String used for pagination
    URLSAFE_KEY_X - A ndb.Key.urlsafe() value
    """
    klass = ndb.Model._lookup_model(kind)
    c = 100

    cursor = Cursor(urlsafe=urlsafe_cursor) if urlsafe_cursor else None
    es, next_cursor, _ = klass.query().fetch_page(c, start_cursor=cursor)

    d = {'keys': [entity.key.urlsafe() for entity in es]}

    if next_cursor:
        d['cursor'] = next_cursor.urlsafe()

    return jsonify(d)

@app.route('/paginate/<kind>')
def start_pagination(kind):
    return paginate(kind)

@app.route('/paginate/<kind>/<cursor>')
def continue_pagination(kind, cursor):
    return paginate(kind, cursor)