Difference between revisions of "AGGREGATE examples"

Revision as of 14:06, 16 July 2015

#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"]}}}])))

@@ Line 29: / Line 29: @@
 </pre>
 <div class=ans>
-pp.pprint(list(db.world.aggregate([{"$match":{"name":"France"}}])
+pp.pprint(list(db.world.aggregate([{"$match":{"name":"France"}}])))
+</div>
+</div>
+<div class=q data-lang="py3">
+<code>$project</code> Allows us to select what fields to display.<br/>
+It can also has the ability to insert new fields and allows you to compare fields against each other without using <code>$where</code>
+<p class=strong>Show population density of al the countries. Population density is population divided by area</p>
+<pre class=def>
+pp.pprint(list(
+    db.world.aggregate([
+        {"$project":{"name":1,"population":1,"area":1,"density":{"$divide":["$population","$area"]}}}
+    ])
 ))
+</pre>
+<div class=ans>
+pp.pprint(list(db.world.aggregate([{"$project":{"name":1,"population":1,"area":1,"density":{"$divide":["$population","$area"]}}}])))
 </div>
 </div>