File "/usr/local/lib/python2.7/dist-packages/mongoengine/connection.py", line 95, in get_connection
    raise ConnectionError(msg)
mongoengine.connection.ConnectionError: You have not defined a default connection

from flask.ext.mongoengine import MongoEngine
db = MongoEngine()
class Currencies(db.Document):
    # meta = {"db_alias": "currencies"}
    name = db.StringField(max_length=40, min_length=3)
    def __unicode__(self):
        return self.name
mongo engine config in app.py:

from models import db
app = Flask(__name__)
app.config['MONGODB_SETTINGS'] = {'DB':'testing'}
db.init_app(app)

from models import Currencies
print Currencies.objects.find()

app.config['MONGODB_SETTINGS'] = {'db':'testing', 'alias':'default'}