View source for FIND Examples


==Introducing the <code>world</code> collection of countries==
  <p>These examples introduce NoSQL using MonogDB and PyMongo under Python3.4. We will be using the find() command on the collection '''world''':</p>
  <div class="hint" title="Techincal details">
  <p>The following is included in the examples but hidden</p>
<pre class=setup>
#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)
</pre>
  </div>

<div class='extra_space' style='width:1em; height:6em;'></div>
<div class=q data-lang="py3">
By default, find() returns the entire contents of a collection. <i>This is equivalent to find({})</i>
<p class=strong>Show all the documents in world</p>
<pre class=def>
pp.pprint(list(
    db.world.find()
))
</pre>
<div class=ans>
pp.pprint(list(db.world.find()))
</div>
</div>

<div class=q data-lang="py3">
It is also possible to just return the first document with find_one(). The Mongo shell equivalent to this is findOne()
<div class="hint" title="When to use list()">
list() is a python function and is a convient way to display a [http://api.mongodb.org/python/current/api/pymongo/cursor.html cursor object]. Alternatively you could use a for loop:
<pre>
for document in db.<collection>.find():
    print(document)
</pre>
find_one() returns a single document, so a list() or loop is not needed.
</div>
<p class=strong>Show the first document of world</p>
<pre class=def>
pp.pprint(db.world.find_one())
</pre>
<div class=ans>
pp.pprint(db.world.find_one())
</div>
</div>

<div class=q data-lang="py3">
It is also possible to specify which document you want by its position.
<div class="hint" title="How to achieve the same with skip() and limit()">
<pre>
print(list(
    db.world.find().skip(49).limit(1)
))
</pre>
</div>
<p class=strong>Get the 50th document of world</p>
<pre class=def>
pp.pprint(
    db.world.find()[50]
)
</pre>
<div class=ans>
pp.pprint(db.world.find()[50])
</div>
</div>

==Querying==
<div class=q data-lang="py3">
By passing arguments to find() we can search for specific documents
<p class=strong>Get all the data concerning france</p>
<pre class=def>
pp.pprint(
    db.world.find_one({"name":"France"})
)
</pre>
<div class=ans>
pp.pprint(db.world.find_one({"name":"France"}))
</div>
</div>

<div class=q data-lang="py3">
By passing a second parameter to find() the output can be limited to certain field(s)<br/>
In this example 1 indicates "true" and 0 indicates "false"<br /><br/>
A feature of MongoDB is the [http://docs.mongodb.org/manual/reference/object-id/ ObjectID] or "_id".<br/> 
This is a unique ID MongoDB adds to each document. Unlike other keys, it has to be <b>explicitly</b> set to false to be excluded from the results set.<br/>
<p class=strong>Get the population of Germany</p>
<pre class=def>
pp.pprint(
    db.world.find_one({"name":"Germany"},{"population":1,"_id":0})
)
</pre>
<div class=ans>
pp.pprint(db.world.find_one({"name":"Germany"},{"population":1,"_id":0}))
</div>
</div>

<div class=q data-lang="py3">
MongoDB also allows comparisons. Syntax:
<pre>
Mongo | MySQL
--------------
$eq   | == 
$gt   | >
$gte  | >=
$lt   | <
$lte  | <=
$ne   | !=, <>
$in   | IN
$nin  | NOT IN
</pre>
<p class=strong>List the countries with a population that's less than 1 million.</p>
<pre class=def>
pp.pprint(list(
    db.world.find({"population":{"$lt":1000000}},{"name":1,"_id":0})
))
</pre>
<div class=ans>
pp.pprint(list(db.world.find({"population":{"$lt":1000000}},{"name":1,"_id":0})))
</div>
</div>

<div class=q data-lang="py3">
It's also possible to have multiple conditions for use in an $and, $or, etc. This can be done in several ways, for example:
<pre>
db.<collection>.find({<first condition>,<second condition>}
db.world.find({"population":{"$lt":1000000},"area":{"$gt":200000})

db.<collection>.find({"$and":[<first condition>,<second condition>]}
db.world.find({"$and":[{"population":{"$lt":1000000}},{"area":{"$gt":200000}}]}
</pre>
<p class=strong>Find the countries with less than 1 million people, but over 200000km<sup>2</sup> area</p>
<pre class=def>
pp.pprint(list(
    db.world.find({"population":{"$lt":1000000},"area":{"$gt":200000}},{"name":1,"_id":0})
))
</pre>
<div class=ans>
pp.pprint(list(db.world.find({"population":{"$lt":1000000},"area":{"$gt":200000}},{"name":1,"_id":0})))
</div>
</div>

<div class=q data-lang="py3">
We can also use lists with $in and $nin:
<p class=strong>Find the continent of Brazil, the United Kingdom, and Ghana.</p>
<pre class=def>
pp.pprint(list(
    db.world.find({"name":{"$in":["Brazil","United Kingdom","Ghana"]}},{"name":1,"continent":1,"_id":0})
))
</pre>
<div class=ans>
pp.pprint(list(db.world.find({"name":{"$in":["Brazil","United Kingdom","Ghana"]}},{"name":1,"continent":1,"_id":0})))
</div>
</div>


<div class=q data-lang="py3">
We can also use lists with $in and $nin:
<p class=strong>Find the continent of Brazil, the United Kingdom, and Ghana.</p>
<pre class=def>
pp.pprint(list(
    db.world.find({"name":{"$in":["Brazil","United Kingdom","Ghana"]}},{"name":1,"continent":1,"_id":0})
))
</pre>
<div class=ans>
pp.pprint(list(db.world.find({"name":{"$in":["Brazil","United Kingdom","Ghana"]}},{"name":1,"continent":1,"_id":0})))
</div>
</div>


<div class=q data-lang="py3">
We can perform pattern matching with Regular Expressions (RegEx)<br />
The Mongo shell syntax is simpler than pymongo:<br/>
<code>db.<collection>.find({<field>:/.*/})</code>
<p class=strong>Show each country that begins with G</p>
<pre class=def>
pp.pprint(list(
    db.world.find({"name":{'$regex':"^G"}},{"name":1,"_id":0})
))
</pre>
<div class=ans>
pp.pprint(list(db.world.find({"name":{'$regex':"^G"}},{"name":1,"_id":0})))
</div>
</div>

You can now move on to [[FIND names]]