Difference between revisions of "AGGREGATE examples"
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"name":1, | "name":1, | ||
}}, | }}, | ||
| − | + | {"$sort":{ | |
"name":1 | "name":1 | ||
}} | }} | ||
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</pre> | </pre> | ||
<div class=ans> | <div class=ans> | ||
| − | pp.pprint(list(db.world.aggregate([{"$project":{"_id":0,"name":1,}}, | + | pp.pprint(list(db.world.aggregate([{"$project":{"_id":0,"name":1,}},{"$sort":{"name":-1}}]))) |
</div> | </div> | ||
</div> | </div> | ||
Revision as of 16:05, 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 the name and population density of all Asian countries. (population/area)
Note that "density" is a new field, made from the result of dividing two existing fields, and that $divide is an aggregate function.
To avoid diving by 0 we do a $match to remove any countries with negligible area, then pipe these results through to $project
pp.pprint(list(
db.world.aggregate([
{"$match":{"area":{"$ne":0},"continent":"Asia"}},
{"$project":{
"_id":0,
"name":1,
"density": {"$divide": ["$population","$area"]}
}}
])
))
pp.pprint(list(db.world.aggregate([{"$match":{"area":{"$ne":0},"continent":"Asia"}},{"$project":{"_id":0,"name":1,"density":{"$divide":["$population","$area"]}}}])))
$sort Allows us to choose how the results are displayed, where 1 is ascending and -1 is descending.
Show the name of all countries in descending order.
pp.pprint(list(
db.world.aggregate([
{"$project":{
"_id":0,
"name":1,
}},
{"$sort":{
"name":1
}}
])
))
pp.pprint(list(db.world.aggregate([{"$project":{"_id":0,"name":1,}},{"$sort":{"name":-1}}])))