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Difference between revisions of "FIND Examples"

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(Created page with "==Introducing the <code>world</code> collection of countries== <p>These examples introduce NoSQL using MonogDB and PyMongo. We will be using the find() command on the collec...")
 
 
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==Introducing the <code>world</code> collection of countries==
+
==Introducing the '''world''' collection of countries==
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  <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>
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<div class='extra_space' style='width:1em; height:6em;'></div>
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<div class="q" data-lang="mongo">
−
<div class=q data-lang="py">
+
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>
−
This example shows how to find the population of a country by searching it's name then limiting what fields are returned.<div class="hint" title="SQL Equivalent">
+
<p class="strong">Show all the documents in world</p>
 +
<pre class="def"><nowiki>db.world.find();</nowiki></pre>
 +
</div>
 +
 
 +
==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>
 +
 
 +
==skip and limit==
 +
<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>
 +
 
 +
==Querying==
 +
<div class="q" data-lang="mongo">
 +
<syntaxhighlight lang="JavaScript" inline>find()</syntaxhighlight> can filter results if a document is used as an argument.
 +
<p class="strong">Get all the data concerning france</p>
 +
<pre class="def"><nowiki>db.world.findOne({name: "France"});</nowiki></pre>
 +
</div>
 +
 
 +
==Using a projection with find==
 +
<div class="q" data-lang="mongo">
 +
By passing a second parameter to <syntaxhighlight lang="JavaScript" inline>find()</syntaxhighlight> the output can be limited to certain field(s)<br/>
 +
In this example '''1''' indicates <syntaxhighlight lang="JavaScript" inline>true</syntaxhighlight> and '''0''' indicates <syntaxhighlight lang="JavaScript" inline>false</syntaxhighlight><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"><nowiki>db.world.findOne({name: "Germany"}, {population: 1, _id: 0});</nowiki></pre>
 +
</div>
 +
 
 +
==Comparisons==
 +
<div class="q" data-lang="mongo">
 +
MongoDB also allows comparisons. Syntax:
 
<pre>
 
<pre>
−
   SELECT population
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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>
 +
 +
==Logical operations $and $or $not==
 +
<div class="q" data-lang="mongo">
 +
It's also possible to have multiple conditions for use in an '''$and''', '''$or''', etc. This can be done in several ways, for example:
 +
<syntaxhighlight lang="JavaScript">
 +
// AND (implicit)
 +
db.<collection>.find({<first condition>, <second condition>});
 +
db.world.find({population: {$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: {$gt: 200000}}]});
 +
</syntaxhighlight>
 +
 +
<p class="strong">Find the countries with less than 1 million people, but over 200000km<sup>2</sup> area.</p>
 +
<pre class="def"><nowiki>db.world.find({population: {$lt: 1000000}, area: {$gt: 200000}}, {name: 1, _id: 0});</nowiki></pre>
 
</div>
 
</div>
−
<p class=strong>Show the population of France</p>
 
−
<pre class=def>
 
−
from pymongo import MongoClient              # Import pymongo
 
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client = MongoClient()                      # Use the default client settings ('mongodb://localhost:27017/')
 
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client.progzoo.authenticate('scott','tiger') # Log in as "Scott" with the password "Tiger"
 
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db = client['progzoo']                      # Use the "progzoo" database
 
  
−
print list(db.world.find({"name":"France"},{"population":1, "_id":0}))
+
==$in and $nin==
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</pre>
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<div class="q" data-lang="mongo">
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<div class=ans>
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Lists can be used with '''$in''' and '''$nin''':
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console.log("Hello World");
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<p class="strong">Find the continent of Brazil, the United Kingdom, and Ghana.</p>
 +
<pre class="def"><nowiki>
 +
db.world.find(
 +
  {name: {$in: ['Brazil', 'Ghana', 'United Kingdom']}},
 +
  {name: 1, continent: 1, _id: 0}
 +
);</nowiki></pre>
 
</div>
 
</div>
 +
 +
==Regular Expressions==
 +
<div class="q" data-lang="mongo">
 +
Pattern matching is possible with Regular Expressions (RegEx)<br/>
 +
<p class="strong">Show each country that begins with G.</p> [[RegEx_Pattern_Matching | RegEx Pattern Matching]]
 +
<pre class="def"><nowiki>
 +
db.world.find(
 +
  {name: {$regex: /^G/}},
 +
  {name: 1, continent: 1, _id: 0}
 +
);</nowiki></pre>
 
</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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