Difference between revisions of "FIND Examples"

By default, find() returns the entire contents of a collection. This is equivalent to find({})

Show all the documents in world

print list(db.world.find())

It is also possible to just return the first document with find_one(). The Mongo shell the equivalent to this is findOne()
To make things easier to understand the first document of world has been made a list of keys used in these examples.

Show the first document of world

from pymongo import MongoClient
client = MongoClient()
client.progzoo.authenticate('scott','tiger')
db = client['progzoo']

print db.world.find_one()

It is also possible to skip documents and limit the amount you return.

Get the 50th document of world

from pymongo import MongoClient
client = MongoClient()
client.progzoo.authenticate('scott','tiger')
db = client['progzoo']

print list(db.world.find().skip(49).limit(1))

By passing arguments to find() we can search for specific documents

Get all the data concerning france

from pymongo import MongoClient
client = MongoClient()
client.progzoo.authenticate('scott','tiger')
db = client['progzoo']

print list(db.world.find({"name":"France"}))

By passing a second parameter to find() the output can be limited to certain field(s)
In this example 1 indicates "true" and 0 indicates "false"

A feature of MongoDB is the ObjectID or "_id".
This is a unique ID MongoDB adds to each document. Unlike other keys, it has to be explicitly set to false to be excluded from the results set.

Get the population of Germany

from pymongo import MongoClient
client = MongoClient()
client.progzoo.authenticate('scott','tiger')
db = client['progzoo']

print list(db.world.find({"name":"Germany"},{"population":1,"_id":0}))

MongoDB also allows comparisons. Syntax:

Mongo | MySQL
--------------
$eq   | == 
$gt   | >
$gte  | >=
$lt   | <
$lte  | <=
$ne   | !=, <>
$in   | IN
$nin  | NOT IN

List the countries with a population that's less than 1 million.

from pymongo import MongoClient
client = MongoClient()
client.progzoo.authenticate('scott','tiger')
db = client['progzoo']

print list(db.world.find({"population":{"$lt":1000000}},{"name":1,"_id":0}))

It's also possible to have multiple conditions for an $and, $or, etc. This can be done in several ways, for example:

db.<collection>.find({<first condition>,<second condition>}
db.world.find({"population":{"$lt":1000000},"area":{"$gt":200000})

db.<collection>.find({"$and":[<first condition>,<second condition>]}
db.world.find({"$and":[{"population":{"$lt":1000000}},{"area":{"$gt":200000}}]}

Find the country with less than 1 million people, but over 200000km² area

from pymongo import MongoClient
client = MongoClient()
client.progzoo.authenticate('scott','tiger')
db = client['progzoo']

print list(db.world.find({"population":{"$lt":1000000},"area":{"$gt":200000}},{"name":1,"_id":0}))