This document introduces Midgard2, an open source content repository for mobile applications. It provides objects instead of SQL for storing data and signals about changes. The data model is scriptable and it allows for synchronization and sharing of data. Midgard2 uses a schema-free approach and stores data as JSON which can be accessed via JavaScript map/reduce queries or pulled via HTTP. It also integrates with CouchDB for a polyglot persistence approach. The document demonstrates how to install and use Midgard2 with examples in PHP, Python and Vala. It also introduces Midgard MVC for building web applications on top of the content repository.

1. Midgard2
Content repository for mobile applications

2. Henri
Bergius
Microblogs: @bergie
http://bergie.iki.fi

3. Content Repository
Don't invent your own file formats

4. Content Repository
Objects instead of SQL

5. Content Repository
Objects instead of SQL
http://xkcd.com/327/

6. Content Repository
Signals about changes

7. Content Repository
Data model is scriptable

8. Content Repository
Synchronization and sharing

9. With a content repository
incredible power is at your disposal

10. Free Content Repositories
• Schema-based, relational • Schema-free
• Query Builder • Javascript map/reduce
• C, glib, libgda • Erlang
• LGPL • Apache License
• D-Bus signals • JSON polling via HTTP
• Library • Daemon
midgard2.org couchdb.apache.org

11. ...and they talk to each other

12. The Midgard Project
• Free software project • Object-Relational
since 1999 Mapping, trees, D-Bus
signals
• Contributors from most
European countries • APIs for C, PHP, Python,
Vala, Objective-C, ...
• Synchronized release
model, every 6 months • Linux, Mac, Maemo

13. Midgard on Maemo 5
Conboy: notes on your phone

14. Midgard on Maemo 5
Workstreamer: project tracking for N900

15. Midgard on the web
Qaiku.com: conversational microblogging

16. Getting started with Midgard

17. Installation
• Linux distribution repositories (Ubuntu, Debian, RHEL,
OpenSuse etc) on OBS:
http://download.opensuse.org/repositories/home:/midgardproject:/mjolnir/
• After that Midgard is just an apt-get install python-
midgard2 or apt-get install
php5-midgard2 away
• Maemo 4 and 5 available
in Extras Devel (soon
Extras)
• On OS X use MacPorts
or the ObjC bundle

18. Objects are defined by MgdSchema
<!-- This will be installed to /usr/share/midgard2/schema/ -->
<type name="midgard_person">
<property name="id" type="unsigned integer" primaryfield="id">
<description>Local non-replication-safe database identifier</description>
</property>
<property name="firstname" type="string" index="yes">
<description>First name of the person</description>
</property>
<property name="lastname" type="string" index="yes">
<description>Last name of the person</description>
</property>
<property name="birthdate" type="datetime">
<description>Birth date of the person</description>
</property>
<property name="email" type="string" index="yes">
<description>Email address of the person</description>
</property>
</type>

19. Midgard API for PHP
<?php
// Load the Midgard2 API extension
dl('midgard2.so');
// Set up the repository config
$config = new midgard_config();
$config->dbtype = 'SQLite';
$config->database = 'midgardexample';
// this will store to SQLite in ~/.midgard2/data/midgardexample.db
// Open a Midgard repository connection
$midgard = midgard_connection::get_instance();
$midgard->open_config($config);
// Prepare storage for your data
midgard_storage::create_base_storage();
midgard_storage::create_class_storage('midgard_person');

20. Midgard API for PHP
// Create a new person object
$person = new midgard_person();
$person->firstname = 'Leif';
$person->lastname = 'Eriksson';
$person->create();
// Query system for all persons with lastname "Eriksson"
$qb = new midgard_query_builder('midgard_person');
$qb->add_constraint('lastname', '=', 'Eriksson');
$persons = $qb->execute();
foreach ($persons as $person)
{
echo "{$person->lastname}, {$person->firstname} has GUID {$person-
>guid}n";
// Add an email address and update
$person->email = 'leif@vinland.no';
$person->update();
}

21. import antigravity
http://xkcd.com/353/

22. import antigravity
# Load the Midgard2 API extension
import _midgard as midgard
# Set up the repository config
configuration = midgard.config()
configuration.dbtype = 'SQLite'
configuration.database = 'midgardexample'
# this will store to SQLite in ~/.midgard2/data/midgardexample.db
# Open a Midgard repository connection
connection = midgard.connection()
connection.open_config(configuration)
# Prepare storage for your data
midgard.storage.create_base_storage()
midgard.storage.create_class_storage('midgard_person')

23. Midgard API: PHP vs. Python
// Create a new person object # Create a new person object
$person = new midgard_person(); person = midgard.mgdschema.midgard_person()
$person->firstname = 'Leif'; person.firstname = 'Leif'
$person->lastname = 'Eriksson'; person.lastname = 'Eriksson'
$person->create(); person.create()
// Query system for all persons with # Query system for all persons with
// lastname "Eriksson" # lastname "Eriksson"
$qb = new qb = midgard.query_builder('midgard_person')
midgard_query_builder('midgard_person'); qb.add_constraint('lastname', '=', 'Eriksson')
$qb->add_constraint('lastname', '=', persons = qb.execute()
'Eriksson'); for person in persons:
$persons = $qb->execute(); print "%s, %s has GUID %s"
foreach ($persons as $person) % (person.lastname, person.firstname,
{ person.guid)
echo "{$person->lastname},” # Add an email address and update
. ” {$person->firstname}” person.email = 'leif@vinland.no'
. “ has GUID {$person->guid}n"; person.update()
// Add an email address and update
$person->email = 'leif@vinland.no';
$person->update();
}

24. Oh, and Vala too!
/* valac --debug --pkg midgard2 -o midgard-vala-example example.vala --vapidir=./ */
using GLib;
using Midgard;
namespace MidgardValaExample {
void main() {
Midgard.init();
Midgard.Config config = new Midgard.Config();
config.read_file ("midgard_test", true);
Midgard.Connection cnc = new Midgard.Connection();
cnc.open_config (config)
Midgard.Object person = new Midgard.Object (cnc, "midgard_person", null);
person.set ("firstname", "Leif");
if (person.create()) {
string guid;
person.get ("guid", out guid);
GLib.print ("Created new person identified by GUID %s n", guid);
}

25. any tools you use, Midgard is there

26. ...maybe even in your finger

27. How about Qt?
• Midgard already
works in PySide
applications
• Would be great to
have proper Qt
support
• Anybody want to
help with this?

28. Tree access
• Parent-child relations
• get_parent()
• list_children()
• Access via named paths
• get_by_path()

29. Extending objects
• Subclasses in MgdSchema
<type name="bossa_attendee" extends="midgard_person">
<property name="likesbeer" type="boolean" default="true" />
</type>
• Ad-hoc additional properties
object.set_parameter('bossa', 'key', 'value')
value = object.get_parameter('bossa', 'key')
• Binary attachments are also supported
• Metadata in repository, file in filesystem
• API provides access to filehandles

30. Midgard MVC
Put your content repository on the web

31. Midgard MVC
• Very efficient MVC
framework for PHP
• Python and D-Bus for
background processing
• Gettext + intl i18n
• TAL templating
• Full WebDAV support
• Git for packaging and
deployment

32. Midgard MVC
Tomboy web synchronization with Midgard

33. Midgard Runtime

34. Explore the possibilities
of content repositories
midgard2.org #midgard on FreeNode @MidgardProject