FIND Examples

2015-12-06T21:29:46Z

40180857: Fixed typo

==Introducing the <code>world</code> collection of countries==
<p>These examples introduce NoSQL using MongoDB. We will be using the find() command on the collection '''world''':</p>
<div class='extra_space' style='width:1em; height:6em;'></div>
<div class=q data-lang=mongo>
By default, <code>find()</code> returns the entire contents of a collection. This is equivalent to <code>find({})</code>
<p class=strong>Show all the documents in world</p>
<pre class=def>
db.world.find()
</pre>
</div>

<div class=q data-lang=mongo>
It is also possible to just return the first document with <code>find_one()</code>. The Mongo shell equivalent to this is <code>findOne()</code>
<div class="hint" title="When to use list()">
<code>list()</code> 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>
<code>find_one()</code> returns a single document, so a <code>list()</code> or loop is not needed.
</div>
<p class=strong>Show the first document of world</p>
<pre class=def>
db.world.findOne()
</pre>
<div class=ans>
db.world.findOne()
</div>
</div>

<div class=q data-lang="mongo">
It is also possible to specify which document to find by its position.
<div>You can achieve the same with skip() and limit()</div>
<pre>
db.world.find().skip(49).limit(1)
</pre>
<p class=strong>Get the 50th document of world</p>
<pre class=def>
db.world.find()[49]
</pre>
<div class=ans>
db.world.find()[49]
</div>
</div>

==Querying==
<div class=q data-lang="mongo">
<code>find()</code> can filter results if a document is used as an argument.
<p class=strong>Get all the data concerning france</p>
<pre class=def>
db.world.find_one({"name":"France"})
</pre>
<div class=ans>
db.world.find_one({"name":"France"})
</div>
</div>

<div class=q data-lang="mongo">
By passing a second parameter to <code>find()</code> 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 <code>_id</code>.<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>
db.world.find_one({"name":"Germany"},{"population":1,"_id":0})</pre>
<div class=ans>
db.world.find_one({"name":"Germany"},{"population":1,"_id":0})</div>
</div>

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

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

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

OR
db.<collection>.find({"$or":[<first condition>,<second condition>]})
db.world.find({"$or":[{"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="mongo">
Lists can be used with <code>$in</code> and <code>$nin</code>:
<p class=strong>Find the continent of Brazil, the United Kingdom, and Ghana.</p>
<pre class=def>
db.world.find({"population":{"$lt":1000000},"area":{"$gt":200000}},{"name":1,"_id":0})</pre>
<div class=ans>
db.world.find({"population":{"$lt":1000000},"area":{"$gt":200000}},{"name":1,"_id":0})</div>
</div>

<div class=q data-lang="mongo">
Pattern matching is possible 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>
db.world.find({"name":{"$in":["Brazil","United Kingdom","Ghana"]}},{"name":1,"continent":1,"_id":0})
</pre>
<div class=ans>
db.world.find({"name":{"$in":["Brazil","United Kingdom","Ghana"]}},{"name":1,"continent":1,"_id":0})
</div>
</div>

FIND Tutorial

2015-12-06T21:29:04Z

40180857: Fixed typo

==Working with the <code>world</code> collection of countries==
<p>This tutorial introduces NoSQL using MongoDB. We will be using the <code>find()</code> command and comparison functions on the collection '''world''' which contains details of around 250 countries of the world:</p>
[[FIND examples]] are available.
<div class='extra_space' style='width:1em; height:6em;'></div>
==Show Germany==
<div class=q data-lang="mongo">
Use <code>find()</code> to show the details of Germany
<p class=strong>Show Germany instead of France</p>
<pre class=def>
db.world.find({name:'France'})
</pre>
<div class=ans>
db.world.find({name:'Germany'})
</div>
</div>

==Eurasia - is that even a thing?==
<div class=q data-lang="mongo">
You can use .pretty() to make the output more readable.
<p class=strong>List all the countries in the continent of "Eurasia"</p>
<pre class=def>
db.world.find({name:'Germany'}).pretty()
</pre>
<div class=ans>
db.world.find({continent:"Eurasia"}).pretty()
</div>
</div>

==Find an area==
<div class=q data-lang="mongo">
You can test numbers as well as strings
<p class=strong>Find the country with an area of exactly 43094</p>
<pre class=def>
db.world.find({gdp:3425956000000}).pretty()
</pre>
<div class=ans>
db.world.find({area:43094}).pretty()
</div>
</div>

==Using $gt==
<div class=q data-lang="mongo">
You can use $gt and $lt to compare numbers and strings ('''$gt''' is greater than, '''$lt''' is less than)
<p class=strong>Show each country with a population of over 250000000</p>
<pre class=def>
db.world.find(
{area:{$gt:9000000}},
{name:1,_id:0}
).pretty()
</pre>
<div class=ans>
db.world.find({population:{$gt:250000000}},{name:1,_id:0}).pretty()
</div>
</div>

==After S==
<div class=q data-lang=mongo">
<p class=strong>List the countries in Europe that come after "S" in the alphabet</p>
<pre class=def>
</pre>
<div class=ans>
db.world.find({population:{$gt:80000000},
continent:"Europe"},
{name:1, _id:0})
</div>
</div>

==Name and Capital==
<div class=q data-lang="mongo">
<p class=strong>Find the name and capital cities for countries with a population of over 70 million</p>
<pre class=def>
</pre>
<div class=ans>
db.world.find(
{population:{$gt:70000000}},
{name:1,capital:1,_id:0}
).pretty()
</div>
</div>

==Using $or==
<div class=q data-lang=mongo>
<p class=strong>Find the countries that have a population of over 200 million or less than 20,000</p>
<pre class=def>
db.world.find({$or:[{name:'Germany'},
{name:'France'}]},
{name:1,population:1,_id:0})
</pre>
<div class=ans>
db.world.find({$or:[{population:{$gt:200000000}},
{population:{$lt:20000 }}]},
{name:1,population:1,_id:0})
</div>
</div>

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FIND Examples

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