AGGREGATE examples

#ENCODING
import io
import sys
sys.stdout = io.TextIOWrapper(sys.stdout.buffer, encoding='utf-16')
#MONGO
from pymongo import MongoClient
client = MongoClient()
client.progzoo.authenticate('scott','tiger')
db = client['progzoo']
#PRETTY
import pprint
pp = pprint.PrettyPrinter(indent=4)

Introducing the aggregation framework

These examples introduce the aggregation framework and its operators. Again we will be using the collection world

$match Allows us to perform queries in a similar way to find()

Show all the details for France

pp.pprint(list(
    db.world.aggregate([
        {"$match":{"name":"France"}}
    ])
))

pp.pprint(list(db.world.aggregate([{"$match":{"name":"France"}}])))

$project Allows us to select what fields to display.
It can also has the ability to insert new fields and allows you to compare fields against each other without using $where

Show population density of al the countries. Population density is population divided by area

pp.pprint(list(
    db.world.aggregate([
        {"$project":{"name":1,"population":1,"area":1,"density":{"$divide":["$population","$area"]}}}
    ])
))

pp.pprint(list(db.world.aggregate([{"$project":{"name":1,"population":1,"area":1,"density":{"$divide":["$population","$area"]}}}])))