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Difference between revisions of "FIND Examples"

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==Introducing the <code>world</code> collection of countries==
+
==Introducing the '''world''' collection of countries==
−
  <p>These examples introduce NoSQL using MonogDB and PyMongo. We will be using the find() command on the collection '''world''':</p>
+
<p>These examples introduce NoSQL using MongoDB. We will be using the <syntaxhighlight lang="JavaScript" inline>find()</syntaxhighlight> command on the '''world''' collection .</p>
−
  <p>A note about the setup</p>
+
<div class="q" data-lang="mongo">
−
  <pre>
+
By default, <syntaxhighlight lang="JavaScript" inline>find()</syntaxhighlight> returns the entire contents of a collection. This is equivalent to <syntaxhighlight lang="JavaScript" inline>find({})</syntaxhighlight>
−
  from pymongo import MongoClient              # Import the pymongo package
+
<p class="strong">Show all the documents in world</p>
−
  client = MongoClient()                      # Use thee default client value('mongodb://localhost:27017/')
+
<pre class="def"><nowiki>db.world.find();</nowiki></pre>
−
  client.progzoo.authenticate('scott','tiger') # Log in using the username scott and the password tiger
+
</div>
−
  db = client['progzoo']                      # Use the 'progzoo' database
 
−
  </pre>
 
−
 
 
−
<div class='extra_space' style='width:1em; height:6em;'></div>
 
−
<div class=q data-lang="py">
 
−
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>
 
−
from pymongo import MongoClient
 
−
client = MongoClient()
 
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client.progzoo.authenticate('scott','tiger')
 
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db = client['progzoo']
 
−
 
 
−
print list(db.world.find())
 
−
</pre>
 
−
<div class=ans>
 
−
from pymongo import MongoClient
 
−
client = MongoClient()
 
−
client.progzoo.authenticate('scott','tiger')
 
−
db = client['progzoo']
 
  
−
print list(db.world.find({}))
+
==find and findOne==
 +
<div class="q" data-lang="mongo">
 +
It is also possible to just return the first document with <syntaxhighlight lang="JavaScript" inline>findOne()</syntaxhighlight>.
 +
<p class="strong">Show the first document of world</p>
 +
<pre class="def"><nowiki>db.world.findOne();</nowiki></pre>
 
</div>
 
</div>
−
</div>
 
−
 
−
<div class=q data-lang="py">
 
−
It is also possible to just return the first document with find_one(). The Mongo shell the equivalent to this is findOne()<br/>To make things easier to understand the first document of world has been made a list of keys used in these examples.
 
−
<p class=strong>Show the first document of world</p>
 
−
<pre class=def>
 
−
from pymongo import MongoClient
 
−
client = MongoClient()
 
−
client.progzoo.authenticate('scott','tiger')
 
−
db = client['progzoo']
 
−
 
−
print list(db.world.find_one())
 
−
</pre>
 
−
<div class=ans>
 
−
from pymongo import MongoClient
 
−
client = MongoClient()
 
−
client.progzoo.authenticate('scott','tiger')
 
−
db = client['progzoo']
 
  
−
print list(db.world.find_one())
+
==skip and limit==
−
</div>
+
<div class="q" data-lang="mongo">
 +
It is also possible to retrieve a specific document based on its position using <syntaxhighlight lang="JavaScript" inline>skip(n-1)</syntaxhighlight> and <syntaxhighlight lang="JavaScript" inline>limit(1)</syntaxhighlight>.<br/>
 +
As this is JavaScript you can also access by index: <syntaxhighlight lang="JavaScript" inline>db.world.find()[n-1];</syntaxhighlight>
 +
<p class="strong">Get the 50th document of world</p>
 +
<pre class="def"><nowiki>db.world.find().skip(49).limit(1);</nowiki></pre>
 
</div>
 
</div>
  
−
<div class=q data-lang="py">
+
==Querying==
−
Let's return the second document by skipping the first one and limiting our find to just one result
+
<div class="q" data-lang="mongo">
−
<p class=strong>Show the second document of world</p>
+
<syntaxhighlight lang="JavaScript" inline>find()</syntaxhighlight> can filter results if a document is used as an argument.
−
<pre class=def>
+
<p class="strong">Get all the data concerning france</p>
−
from pymongo import MongoClient
+
<pre class="def"><nowiki>db.world.findOne({name: "France"});</nowiki></pre>
−
client = MongoClient()
 
−
client.progzoo.authenticate('scott','tiger')
 
−
db = client['progzoo']
 
−
 
 
−
print list(db.world.find().skip(1).limit(1))
 
−
</pre>
 
−
<div class=ans>
 
−
from pymongo import MongoClient
 
−
client = MongoClient()
 
−
client.progzoo.authenticate('scott','tiger')
 
−
db = client['progzoo']
 
−
 
 
−
print list(db.world.find().skip(1).limit(1))
 
−
</div>
 
 
</div>
 
</div>
  
−
<div class=q data-lang="py">
+
==Using a projection with find==
−
What if we want the last document in a collection? For this we can use count()<br/>
+
<div class="q" data-lang="mongo">
−
Conveniently, db.collection.find().count() and db.collection.count() are identical.
+
By passing a second parameter to <syntaxhighlight lang="JavaScript" inline>find()</syntaxhighlight> the output can be limited to certain field(s)<br/>
−
<p class=strong>Show the amount of documents in the collection and the last document</p>
+
In this example '''1''' indicates <syntaxhighlight lang="JavaScript" inline>true</syntaxhighlight> and '''0''' indicates <syntaxhighlight lang="JavaScript" inline>false</syntaxhighlight><br/><br/>
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<div class="hint" title="Why and when to use list">
+
A feature of MongoDB is the [http://docs.mongodb.org/manual/reference/object-id/ ObjectID] or '''_id'''.<br/>
−
find() returns a [http://api.mongodb.org/python/current/api/pymongo/cursor.html cursor object]. A way to see the contents is to wrap a list. You can avoid this by using Mongo shell
+
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"><nowiki>db.world.findOne({name: "Germany"}, {population: 1, _id: 0});</nowiki></pre>
 
</div>
 
</div>
−
<pre class=def>
 
−
from pymongo import MongoClient
 
−
client = MongoClient()
 
−
client.progzoo.authenticate('scott','tiger')
 
−
db = client['progzoo']
 
−
 
−
print db.world.count()
 
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print list(db.world.find().skip(db.world.count()-1))
 
−
</pre>
 
−
<div class=ans>
 
−
from pymongo import MongoClient
 
−
client = MongoClient()
 
−
client.progzoo.authenticate('scott','tiger')
 
−
db = client['progzoo']
 
  
−
print db.world.count()
+
==Comparisons==
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print list(db.world.find().skip(db.world.count()-1))
+
<div class="q" data-lang="mongo">
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</div>
+
MongoDB also allows comparisons. Syntax:
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</div>
 
−
==Querying==
 
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<div class=q data-lang="py">
 
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By passing arguments to find() we can search for specific documents
 
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<p class=strong>Get all the data concerning france</p>
 
−
<div class="hint" title="SQL Equivalent">
 
 
<pre>
 
<pre>
−
SELECT *
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<nowiki>
−
FROM world
+
Mongo | MySQL
−
WHERE name = 'France'
+
--------------
 +
$eq  | ==  
 +
$gt  | >
 +
$gte  | >=
 +
$lt  | <
 +
$lte  | <=
 +
$ne  | !=, <>
 +
$in  | IN
 +
$nin  | NOT IN
 +
</nowiki>
 
</pre>
 
</pre>
 +
<p class="strong">List the countries with a population that's less than 1 million.</p>
 +
<pre class="def"><nowiki>db.world.find({population: {$lt: 1000000}}, {name: 1, _id: 0});</nowiki></pre>
 
</div>
 
</div>
−
<pre class=def>
 
−
from pymongo import MongoClient
 
−
client = MongoClient()
 
−
client.progzoo.authenticate('scott','tiger')
 
−
db = client['progzoo']
 
  
−
print list(db.world.find({"name":"France"}))
+
==Logical operations $and $or $not==
−
</pre>
+
<div class="q" data-lang="mongo">
−
<div class=ans>
+
It's also possible to have multiple conditions for use in an '''$and''', '''$or''', etc. This can be done in several ways, for example:
−
from pymongo import MongoClient
+
<syntaxhighlight lang="JavaScript">
−
client = MongoClient()
+
// AND (implicit)
−
client.progzoo.authenticate('scott','tiger')
+
db.<collection>.find({<first condition>, <second condition>});
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db = client['progzoo']
+
db.world.find({population: {$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}}]});
 +
</syntaxhighlight>
  
−
print list(db.world.find({"name":"France"}))
+
<p class="strong">Find the countries with less than 1 million people, but over 200000km<sup>2</sup> area.</p>
−
</div>
+
<pre class="def"><nowiki>db.world.find({population: {$lt: 1000000}, area: {$gt: 200000}}, {name: 1, _id: 0});</nowiki></pre>
 
</div>
 
</div>
  
−
<div class=q data-lang="py">
+
==$in and $nin==
−
By passing a second parameter to find() the output can be limited to certain field(s)<br/>
+
<div class="q" data-lang="mongo">
−
In this example 1 indicates "true" and 0 indicates "false"<br /><br/>
+
Lists can be used with '''$in''' and '''$nin''':
−
A feature of MongoDB is the [http://docs.mongodb.org/manual/reference/object-id/ ObjectID] or "_id".<br/>
+
<p class="strong">Find the continent of Brazil, the United Kingdom, and Ghana.</p>
−
This is a unique ID MongoDB adds to each document. Unlike other keys, it has to be <b>explicitly</b> set to false.
+
<pre class="def"><nowiki>
−
<p class=strong>Get the population of Germany</p>
+
db.world.find(
−
<div class="hint" title="SQL Equivalent">
+
  {name: {$in: ['Brazil', 'Ghana', 'United Kingdom']}},
−
<pre>
+
  {name: 1, continent: 1, _id: 0}
−
SELECT population
+
);</nowiki></pre>
−
FROM world
 
−
WHERE name = 'Germany'
 
−
</pre>
 
 
</div>
 
</div>
−
<pre class=def>
 
−
from pymongo import MongoClient
 
−
client = MongoClient()
 
−
client.progzoo.authenticate('scott','tiger')
 
−
db = client['progzoo']
 
  
−
print list(db.world.find({"name":"France"},{"population":1,"_id":0}))
+
==Regular Expressions==
−
</pre>
+
<div class="q" data-lang="mongo">
−
<div class=ans>
+
Pattern matching is possible with Regular Expressions (RegEx)<br/>
−
from pymongo import MongoClient
+
<p class="strong">Show each country that begins with G.</p> [[RegEx_Pattern_Matching | RegEx Pattern Matching]]
−
client = MongoClient()
+
<pre class="def"><nowiki>
−
client.progzoo.authenticate('scott','tiger')
+
db.world.find(
−
db = client['progzoo']
+
  {name: {$regex: /^G/}},
−
 
+
  {name: 1, continent: 1, _id: 0}
−
print list(db.world.find({"name":"France"},{"population":1,"_id":0}))
+
);</nowiki></pre>
−
</div>
 
 
</div>
 
</div>

Latest revision as of 15:12, 17 October 2018

Introducing the world collection of countries

These examples introduce NoSQL using MongoDB. We will be using the find() command on the world collection .

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

Show all the documents in world

db.world.find();

find and findOne

It is also possible to just return the first document with findOne().

Show the first document of world

db.world.findOne();

skip and limit

It is also possible to retrieve a specific document based on its position using skip(n-1) and limit(1).
As this is JavaScript you can also access by index: db.world.find()[n-1];

Get the 50th document of world

db.world.find().skip(49).limit(1);

Querying

find() can filter results if a document is used as an argument.

Get all the data concerning france

db.world.findOne({name: "France"});

Using a projection with find

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

db.world.findOne({name: "Germany"}, {population: 1, _id: 0});

Comparisons

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.

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

Logical operations $and $or $not

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

// 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}}]});

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

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

$in and $nin

Lists can be used with $in and $nin:

Find the continent of Brazil, the United Kingdom, and Ghana.

db.world.find(
   {name: {$in: ['Brazil', 'Ghana', 'United Kingdom']}},
   {name: 1, continent: 1, _id: 0}
);

Regular Expressions

Pattern matching is possible with Regular Expressions (RegEx)

Show each country that begins with G.

RegEx Pattern Matching 
db.world.find(
  {name: {$regex: /^G/}},
  {name: 1, continent: 1, _id: 0}
);
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