Presented at the YAPC::Europe conference in Pisa, Italy

1. Introduction to CouchDB
Jon Allen (JJ) – jj@opusvl.com
YAPC::Europe 2010
Introduction to CouchDB
Open Source Business Systems
www.opusvl.com

2. What is CouchDB?
• Document Oriented Database
Introduction to CouchDB
Open Source Business Systems
www.opusvl.com

3. What is CouchDB?
• Document Oriented Database
– No schema
• Stores "documents" (i.e. data structures)
– No SQL
• Uses "MapReduce" queries written in JavaScript
Introduction to CouchDB
Open Source Business Systems
www.opusvl.com

4. What is CouchDB?
• Document Oriented Database
– No schema
• Stores "documents" (i.e. data structures)
– No SQL
• Uses "MapReduce" queries written in JavaScript
• Written in Erlang
• REST API
• Replication, scalability
Introduction to CouchDB
Open Source Business Systems
www.opusvl.com

5. Why use CouchDB?
• Store complex data structures (JSON)
• Store variable data structures (no schema)
• De-normalised / self contained
• Add attachments to documents
• Scalable and fault tolerant
• Better fit for certain problem domains
– Messaging
– CMS
Introduction to CouchDB
Open Source Business Systems
www.opusvl.com

6. Using CouchDB from Perl
• HTTP REST API
• No DBI, DBD, DBIx::Class etc
• CPAN modules
– CouchDB::Client
– AnyEvent::CouchDB
Introduction to CouchDB
Open Source Business Systems
www.opusvl.com

7. Creating a database
use CouchDB::Client;
use Try::Tiny;
my $client = CouchDB::Client->new(
uri => 'http://localhost:5984'
);
my $db = $client->newDB('jj_test'); # lower case!
try {
$db->create;
} catch {
die "Could not create DB";
};
Introduction to CouchDB
Open Source Business Systems
www.opusvl.com

8. Inserting a document
my $client = CouchDB::Client->new();
my $db = $client->newDB('jj_test');
my $doc = $db->newDoc('docid', undef, {
type => 'message',
text => 'Hello, World',
to => ['JJ', 'Barbie', 'Brian'],
});
try {
$doc->create;
} catch {
die "Could not create document";
};
Introduction to CouchDB
Open Source Business Systems
www.opusvl.com

9. Inserting a document
my $client = CouchDB::Client->new();
my $db = $client->newDB('jj_test');
my $doc = $db->newDoc('docid', undef, {
type => 'message',
text => 'Hello, World',
to => ['JJ', 'Barbie', 'Brian'],
});
try { Document ID, Revision ID
$doc->create; must be unique
} catch {
die "Could not create document";
};
Introduction to CouchDB
Open Source Business Systems
www.opusvl.com

10. CouchDB GUI
Introduction to CouchDB
Open Source Business Systems
www.opusvl.com

11. Querying documents
All Documents
Map function
Key, Value
Key, Value Key, Value
Query by Key
Key, Value
Key, Value
Key, Value
Introduction to CouchDB
Open Source Business Systems
www.opusvl.com

12. Views
• A view is a JavaScript function
– Like a stored procedure in SQL
• Map function is executed on every document in
the database
• Emits key/value pairs
– Can emit 0, 1, or more KV pairs for each document
in the database
– Keys and values can be complex data structures
• KV pairs are then ordered and indexed by key
Introduction to CouchDB
Open Source Business Systems
www.opusvl.com

13. Queries
• Queries are run against views
– i.e. searches the "key" of the list of KV pairs
• Query types:
– Exact: key = x
– Range: key is between x and y
– Multiple: key is in list (x,y,z)
• Reduce functions
– e.g. count, sum, group
Introduction to CouchDB
Open Source Business Systems
www.opusvl.com

14. Designing a view
• Show messages for a specific user
// This is JavaScript
function(doc) {
if (doc.type && doc.to && doc.text) {
if (doc.type == 'message') {
for (var dest in doc.to) {
emit(doc.to[dest], doc.text);
}
}
}
}
Introduction to CouchDB
Open Source Business Systems
www.opusvl.com

15. Creating a view
• Can either use the GUI or the API
• View stored in database as a "Design Document"
– A design document can contain multiple views
• Example
– Design document "_design/myview"
– View name "messages_to"
Introduction to CouchDB
Open Source Business Systems
www.opusvl.com

16. Querying a view
use Data::Dumper;
my $client = CouchDB::Client->new();
my $db = $client->newDB('jj_test');
my $view = $db->newDesignDoc('_design/myview')
->retrieve;
my $result = try {
$view->queryView('messages_to', (key => 'JJ'));
} catch {
die "Could not query view";
};
say Dumper($result);
Introduction to CouchDB
Open Source Business Systems
www.opusvl.com

17. Query results
varos:talk_scripts jj$ perl5.10.1 query_view.pl
$VAR1 = {
'total_rows' => 3,
'rows' => [
{
'value' => 'Hello, World',
'id' => 'docid',
'key' => 'JJ'
}
],
'offset' => 2
};
Introduction to CouchDB
Open Source Business Systems
www.opusvl.com

18. Conclusion
• Different mindset to SQL database
• Quite low-level, but very powerful
• Additional features
– Replication
– Document revisions
– Reduce functions
– Changes API
• More information: http://books.couchdb.org/relax
Introduction to CouchDB
Open Source Business Systems
www.opusvl.com

19. KTHKSBYE!
Thank you for listening!
Any questions?
http://www.opusvl.com
http://perl.jonallen.info/talks
Introduction to CouchDB
Open Source Business Systems
www.opusvl.com