NAME¶
MongoDB::Tutorial - Getting started with MongoDB
VERSION¶
version v0.705.0.0
DESCRIPTION¶
The tutorial runs through the basic functionality of the MongoDB package. This
is a good starting point if you have never used MongoDB before.
The tutorial assumes that you are running a MongoDB database server locally on
the default port. You can download Mongo from <
http://www.mongodb.org>.
TERMINOLOGY¶
Document-oriented database terms and their relational equivalents:
- Database
- Database
- Collection
- Table
- Document
- Record or row
- MongoDB::OID
- Autoincrementing primary key
PREAMBLE¶
"use MongoDB" loads most of the packages you'll need to interact with
MongoDB: MongoDB::MongoClient, MongoDB::Database, MongoDB::Collection, and
MongoDB::Cursor. To use special Mongo data types (see MongoDB::DataTypes), you
have to include them separately. So, usually, to use Mongo, you'll start with
at least:
use MongoDB;
use MongoDB::OID;
CONNECTING¶
To get started, we have to connect to the database server. Because it's running
locally on the default port, we need not pass any parameters to the
MongoDB::MongoClient constructor:
my $client = MongoDB::MongoClient->new;
Now we're connected to the database server. Next we need a database to work
with, we'll call it "tutorial". You need not do anything special to
create the database, Mongo will create it on the fly.
my $db = $client->get_database( 'tutorial' );
The last part of the preliminary setup is to choose a collection. We'll be using
the "users" collection to start out.
my $users = $db->get_collection( 'users' );
Again, there is no need to create the collection in advance, it will be created
as needed.
CRUD¶
Creating Documents¶
Inserting
To add a document to the collection, we use the "insert" function. It
takes a hash reference which is saved to the collection.
$users->insert({"name" => "Joe",
"age" => 52,
"likes" => [qw/skiing math ponies/]});
Now there is a user in the collection.
MongoDB::OIDs
When a document is inserted, it is given a "_id" field if one does not
already exist. By default, this field is a MongoDB::OID, 12 bytes that are
guaranteed to be unique. The "_id" field of the inserted document is
returned by the "insert" method.
my $id = $users->insert({"name" => "Bill"});
An efficient way to insert documents is to send many at a time to the database
by using "batch_insert", which returns an array of the
"_id" fields of the documents inserted.
my @ids = $users->batch_insert(\@many_users);
Retrieving Documents¶
Queries
To retrieve documents that were saved to a collection, we can use the
"find" method.
my $all_users = $users->find;
To query for certain criteria, say, all users named Joe, pass the query a hash
with the key/value pair you wish to match:
my $some_users = $users->find({"name" => "Joe"});
You can match array elements in your queries; for example, to find all users who
like math:
my $geeks = $users->find({"likes" => "math"});
This being Perl, it is important to mention that you can also use regular
expressions to search for strings. If you wanted to find all users with the
name John and all variations of said name, you could do:
my $john = $users->find({"name" => qr/joh?n/i});
See "Regular Expressions" in MongoDB::DataTypes for more information.
Ranges
As queries are hashes, they use a special syntax to express comparisons, such as
"x < 4". To make the query a valid hash, Mongo uses $-prefixed
terms. For example, "x < 4" could be expressed by:
my $doc321 = $collection->find({'x' => { '$lt' => 4 }});
Comparison operators can be combined to get a range:
my $doc32 = $collection->find({'x' => { '$gte' => 2, '$lt' => 4 }});
Cursors
"find" returns a MongoDB::Cursor, which can be iterated over. It
lazily loads results from the database. The following prints all of the users'
names:
while (my $doc = $all_users->next) {
print $doc->{'name'}."\n";
}
A cursor can also be converted into an array of hash references. For example, to
print the "name" field of the first result:
my @arr = $geeks->all;
print $arr[0]->{'name'}."\n";
Updating Documents¶
"$"-operators
To change a document after it has been saved to the database, you must pass
"update" two arguments. The first is a query argument, identical to
the previous section, to identify the document you want to change. The second
is an argument that describes the change that you wish to make.
The change is described by $-prefixed descriptors. For example, to increment a
field, we would write:
$users->update({"_id" => $id}, {'$inc' => {'age' => 1}});
To add an element to an array, we can use $push. So, to add an element to the
"likes" array, we write:
$users->update({"_id" => $id}, {'$push' => {'likes' => 'reading'}});
To add a new field or change the type or value of an existing field, we use
$set. For example, to change the _id field to a username, we would say:
$users->update({"_id" => $id}, {'$set' => {'name' => 'joe_schmoe'}});
Options
By default, "update" operates on one matching document, and does
nothing if no document matches the query. There are two options available to
change this behavior.
Suppose we want to add a "gift" field to everyone whose birthday it is
today. One way would be to find every person whose birthday it was and iterate
through the user documents, updating each one. However, it would be much
faster and easier to update multiple documents at once. We can do this by
using an optional third parameter with "update":
my $today = DateTime->now;
my $tomorrow = DateTime->now->set('day' => $today->day+1);
$users->update({"bday" => {'$gte' => $today, '$lte' => $tomorrow}},
{'$set' => {'gift' => $gift}},
{'multiple' => 1});
(This functionality was added in version 1.1.3 of the database and will not work
in earlier versions.) Sometimes we may want update to create an element if it
does not already exist. This is called an 'upsert' (a combination of an update
and an insert). For example, the same code could be used for creating and
updating a log document:
$pageviews->update({"url" => "www.example.com"},
{'$inc' => {"views" => 1}},
{'upsert' => 1});
If the pageview counter for www.example.com did not exist yet, it would be
created and the "views" field would be set to 1. If it did exist,
the "views" field would be incremented.
Deleting Documents¶
To delete documents, we use the "remove" method. It takes the same
type of hash queries do:
$users->remove({"name" => "Joe"});
Calling "remove" with no parameters removes all of the objects in a
collection. It does not delete the collection, though (in that in that it will
still appear if the user lists collections in the database and the indexes
will still exist). To remove a collection entirely, call "drop":
$users->drop;
"drop" can also be used for whole databases:
$db->drop;
MONGODB BASICS¶
Database Commands¶
There are a large number of useful database commands that can be called directly
with $db->run_command. For example, to drop a collection, you can use:
$db->run_command({drop => $collection_name});
"drop" only requires one key/value pair, but for commands that require
multiple fields, Mongo expects key/value pairs to be in a certain order. It
will not recognize the command if they are not ordered command name first.
Thus, if you are running a database command, you should probably use
Tie::IxHash instead of a normal hash (normal hashes are not ordered).
For example, you can use a database command to create a capped collection like
so:
my $cmd = Tie::IxHash->new("create" => "posts",
"capped" => boolean::true,
"size" => 10240,
"max" => 100);
$db->run_command($cmd);
This will create a capped collection called "posts" in the current
database. It has a maximum size of 10240 bytes and can contain up to 100
documents.
NEXT STEPS¶
Now that you know the basic syntax used by the Perl driver, you should be able
to translate the JavaScript examples in the main MongoDB documentation
(<
http://www.mongodb.org>) into Perl.
Check out MongoDB::Examples for more examples.
AUTHORS¶
- •
- David Golden <david.golden@mongodb.org>
- •
- Mike Friedman <friedo@mongodb.com>
- •
- Kristina Chodorow <kristina@mongodb.org>
- •
- Florian Ragwitz <rafl@debian.org>
COPYRIGHT AND LICENSE¶
This software is Copyright (c) 2014 by MongoDB, Inc..
This is free software, licensed under:
The Apache License, Version 2.0, January 2004