Introduction to CouchDB
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CouchDB is a document-oriented NoSQL database that uses JavaScript for querying. It stores data as JSON documents without a predefined schema and uses MapReduce functions for queries. Documents can be inserted and queried via a REST API. Views allow querying documents by indexing them with keys generated by map functions. Queries run against views to search indexed keys in various ways.
![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
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![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
$doc->create; must be unique
} catch {
die "Could not create document";
};
Introduction to CouchDB
Open Source Business Systems
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![Designing a view
• Show messages for a specific user
// This is JavaScript
function(doc) {
if (doc.type && doc.to && doc.text) {
if (doc.type == 'message') {
for (var dest in doc.to) {
emit(doc.to[dest], doc.text);
}
}
}
}
Introduction to CouchDB
Open Source Business Systems
www.opusvl.com](https://image.slidesharecdn.com/introductiontocouchdbopusvl-120824050036-phpapp02/85/Introduction-to-CouchDB-14-320.jpg)
![Query results
varos:talk_scripts jj$ 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
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Introduction to CouchDB
- 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