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NAME ^

Myco::Devel - myco Developer's Guide.

DESCRIPTION ^

This guide is intended for developers wanting to build applications with myco. You should have a decent grasp of the Perl programming language, or else a solid grasp of another programming language (C, PHP, etc.). Familiarity with Object Oriented Programming (OOP) techniques and test-first methodology of developing programs (such as outlined in the "eXtreme Programming" method) also go a long way toward writing sound applications, and making the best use of features offered in myco.

Our goal in this manual is to write and run a small application based on the myco framework.

Most likely, you will also be functioning as your own sysadmin. If so, please consult the Myco System Administration Guide for how-tos on installing Perl, PostresSQL, module dependencies, myco-deploying the database, etc. This document will repeat some of the details from the Admin guide along the way.

Also note that the assumption running through this guide that you're working on some variant of Unix or Linux. This is just to Keep It Simple Stupid. Nothing would thrill us more than to see widespread Windows myco-deployments of myco. Please hit the mailing list or the myco blog (http://www.mycohq.com/) if you are attempting such a thing and run into trouble.

Myco::App::Guitar - first myco entity class! ^

The simplest way to get started, after completing installation and initial configuration of myco, is to utilize myco-mkentity to create a new Myco entity class and its companion test class. Depending on how you like to structure your module files and what testing framework you like to use (myco-mkentity and myco-testrun currently use Test::Class with Test::Unit), this may not suit you. But for this guide, it'll have to do :)

First, be sure that you've set a couple environment variables. Assuming you've downloaded and untarred/unzipped the myco distribution into your home directory and renamed it just 'myco', in sh or bash:

  export MYCO_ROOT=/usr/home/yourhomedir/myco

In csh or tcsh:

  setenv MYCO_ROOT /usr/home/yourhomedir/myco

Put it in your .bashrc or .cshrc for permanence, if you like. Now navigate there:

  cd $MYCO_ROOT

Now, after contemplating the object you'd like to model in your class and the name you want to give to it, run myco-mkentity:

  ./bin/myco-mkentity Myco::App::Guitar

Though you can name your class anything, a good place to start is to park it within the Myco perl namespace, making use of the 'App' area. This has been historically used as a collection point or sandbox for developing myco applications. Anyway, using myco-mkentity requires you to do it this way.

You can now poke around your new class file:

   vi lib/Myco/App/Guitar.pm

and your companion test class file:

   vi test/Myco/App/Guitar/Test.pm

Once you're satisfied its all there, give the test a whirl!

  % ./bin/myco-testrun Myco::App::Guitar::Test
  ......
  Time:  0 wallclock secs ( 0.01 usr +  0.01 sys =  0.02 CPU)

By default, your new test class will not test for persistence bahavior:

  skip_persistence => 1 # in the %test_parameters hash of your test class

This is desirable, since its entirely possible that you want to simply use the myco framework to write classes to work in-memory only, and not persist as objects in a database. In this case, you'd proceed to write your code, but all attributes would be of a transient nature. But in most cases - such as now - you'll want to utilize persistence. So turn persistence testing on:

  skip_persistence => 0

and run the test again. It should crash and burn, ending like this:

  !!!FAILURES!!!
  Test Results:
  Run: 6, Failures: 0, Errors: 3

So, we now want to configure your class in the myco framework to be persistent, so that these six initial persistence tests will pass.

The Guitar.pm module file generated my myco-mkentity provides two dummy attributes (fooattrib and barattrib) to get persistence started. This should suffice to prove that persistence will work. One thing you might want to do before remyco-deploying the database is to specify your own DB table name. In the Myco::Entity::Meta object creation near the top of the class, setting the database table name:

  tangram => { table => 'guitar', }

You can leave it commented out, too - table name will be generated automatically for your class when we myco-recycle the database, as long as you add your class' name to the SCHEMA_ENTITY_CLASSES array in the schema hash in myco.conf:

              SCHEMA_ENTITY_CLASSES => [
                                        qw(
                                            Myco::App::Guitar
                                          )
                                       ],

If you ran the installation tests, myco.conf will have been created for you based on your responses to questions about your environment. If not, copy the file myco.conf-dist to myco.conf and flesh it out. Regardless you need to add the name of your entity class yourself at this point.

Now myco-deploy the new class to the database...

  ./bin/myco-deploy

...looking for output indicating that your 'guitar' table was created...

  guitar myco-deployed
  Schema Deployed

...and run the test again:

  ./bin/myco-testrun Myco::App::Guitar::Test

All six basic entity tests should have passed. If you're suspicious that something should have failed, then you must be a test-first coder! Seriously, testing is good to do in parellel with (or, better, anterior to) writing your code. But myco's testing framework utilizes inheritance and other OO virtues to automate all the repetitious object persistence and entity class testing you'd normally have to do for each case. This means that, when you just want to model, in our case, a basic guitar and its attributes, you really don't have to write test code for it - its built into the framework!

But before we flesh Guitar.pm. First we'll replace the stock attributes with ones more guitar-ish. Try these on for size:

  $md->add_attribute(name => 'make',
                     type => 'int',
                     values => [0..3],
                     value_labels => {
                                      0 => 'Gibson',
                                      1 => 'Fender',
                                      2 => 'Paul Reed Smith',
                                      3 => 'Ibanez',
                                     },
                    );

  $md->add_attribute(name => 'model',
                     type => 'string',
                    );

Simple, right? Here we're outlining the make/model with a Tangram integer and string data type, respectively. Here's one more:

  $md->add_attribute( name => 'strings',
                      type => 'flat_array',
                      tangram_options => { table => 'guitar_strings', },
                    );

The last one may seem silly, since most guitars have six strings, but let's not forget about the guitar's poor cousin - the bass guitar, or various bastardizations like the seven-string, twelve-string or 'Chapman Stick' :)

There's many ways to model your attributes (TIMTOWDI), including using sets of objects, etc. Myco is tightly bound to the Tangram data mapping framework, so best to consult its documentation for more info. See Tangram::Type for more on the data types available for persistification. Here we're modeling strings as a perl array.

Now get rid of any references to those dummy attributes, 'fooattrib' and 'barattrib' in Guitar.pm and its Test.pm file:

In Line 70 of your Test.pm change this:

   simple_accessor => 'foottrib',

to this:

   simple_accessor => 'make',

As the comment above says, simple_accessor is "A scalar attribute that can be used for testing". You can further flesh out the %test_parameters hash to have the test framework automatically run your new attributes through the gauntlet. This can be very useful (even necessary) for objects that have required attributes using complex data types. But that's not the case with our current example.

Since our data schema has changed, let's myco-recycle the database!

  ./bin/myco-recycle

Again you'll see output to the effect that your guitar table was remyco-deployed.

Building a guitar ^

Now, let's write a simple perl script to build our very own guitar!

  #!/usr/bin/perl -w
  use strict;

  use Myco;

  # Get database connection paramters from myco.conf - very handy!
  use Myco::Config qw(:database);
  Myco->db_connect(DB_DSN, DB_USER, DB_PASSWORD);

  # Make it a Fender!
  my $guitar = Myco::App::Guitar->new( make => 1 );

  print "Its a guitar!\n" if ref $guitar eq 'Myco::App::Guitar';

  $guitar->set_make(0);              # Changed my mind, now its a Gibson
  $guitar->set_model('Les Paul');
  my @strings = qw(B E A D G B E);   # Seven strings - rare!
  $guitar->set_strings( \@strings );

  my $id = $guitar->save; 

  print "The Tangram OID for your new guitar is: $id\n" if $id;

  # Do a myco/tangram query
  my $guitar_ = Myco->remote('Myco::App::Guitar');
  my @results = Myco->select( $guitar_, $guitar_->{model} eq 'Les Paul' );

  print "Guitar was saved and selected!\n"
      if $results[0]->id == $id;

  $guitar->destroy;

  Myco->db_disconnect;

Creating reusable queries in myco ^

One extremely sexy feature of myco is the ability to model (and store persistently) the behavior of a Tangram query object. This is accomplished by specifying as metadata the information you'd normally use to write a Tangram query in raw perl code - things such as attribute names, remote objects, boolean operators used to join clauses of the query together, and even the various methods Tangram::Expr used for the different Tangram data types.

You saw how our query was done in just two lines in the above example. Not much need to elaborate on that. However, when writing queries that involve many and more complex attributes such as object sets, optional filter clauses, etc., these queries can quickly become monstrous. Building an abstract query specification as a Myco::Entity::Meta::Query object is the best way to save yourself a lot of coding later on in your application.

So, let's rewrite our above example in a slightly different way (just to prove TMTOWTDI), while also replacing our simple two line query with one that can do a little more, but this time as a query spec in Guitar.pm.

Find the commented section - "Query Specifications" - near the top of Guitar.pm. Let's build our query spec here:

  my $queries = sub {

     my $md = shift; # Metadata object

     $md->add_query( name => 'Test Guitar Query',
                     remotes => { '$guitar_' => 'Myco::App::Guitar', },
                     result_remote => '$guitar_',
                     params => {
                                 param_make => [ qw($guitar_ make) ],
                                 param_model => [ qw($guitar_ model 1) ],
                                 param_string => [ qw($guitar_ strings 1) ],
                               },
                     filter => {
                                 parts => [
                                            { remote => '$guitar_',
                                              attr => 'make',
                                              oper => 'eq',
                                              param => 'param_last',
                                              part_join_oper => '&', },
                                            { remote => '$guitar_',
                                              attr => 'model',
                                              oper => 'eq',
                                              param => 'param_model',
                                              part_join_oper => '&', },
                                            { remote => '$guitar_',
                                              attr => 'strings',
                                              oper => 'includes',
                                              param => 'param_string' },
                                          ],
                               },
                   );
  };

We specify our query inside an anonymous subroutine. This is so we can create as many for our class as we like, and so it can more easily be passed to the Myco::Entity::Meta method, activate_class. While we're at it, let's do that. Find the method call at the bottom of Guitar.pm:

  $md->activate_class( queries => $queries );

For a full account of this structure, see Myco::QueryTemplate. A couple of things to note in passing are the params hash, which specifies the remote object containing the attribute, the actual attribute name, as well as a boolean flag to indicate that a param is optional. So, in this query, only the first param is required. The params hash is keyed by the attribute alias we'll use it comes time to actually run the query and pass in the params. To illustrate that you can use any descriptive alias you like, I've prepended each hash key in params with a param_. You could've also call these three params 'foo_1', 'foo_2', and 'foo_3', though that would be a bit obscure :) Most often you'd just key this hash with the actual attribute names. Just remember that only the hash values in the array will be used to construct the query.

No let's let's rewrite our script:

  #!/usr/bin/perl -w
  use strict;

  use Myco;

  use Myco::Config qw(:database);
  Myco->db_connect(DB_DSN, DB_USER, DB_PASSWORD);

  my $guitar = Myco::App::Guitar->new( make => 0,
                                       model => 'Stratocaster',
                                       strings => [qw(E A B C D E F G)] );
  my $id = $guitar->save;

  print "The Tangram OID for your new guitar is: $id\n" if $id;

  # Let's dig into the metadata to get our query
  my $class_metadata = Myco::App::Guitar->introspect;
  my $queries = $class_metadata->get_queries;

  my $guitar_query = $queries->{'Test Guitar Query'};
  my $its_a_myco_query = ref $guitar_query eq 'Myco::Entity::Meta::Query';
  print "Its a query!\n" if $its_a_myco_query;

  my %run_params = ( param_make => '1',
                     param_model => 'Stratocaster',
                     param_string => 'B' );

  my @results = $guitar_query->run_query( %run_params );

  print "Guitar was saved and selected!\n"
    if $results[0]->id == $id;

Pretty cool! When you're just starting out doing Tangram queries, a method that you might find helpful is get_filter_string in Myco::QueryTemplate.

For instance, this...

  print $guitar_query->get_filter_string( \%params );

...should yield this:

  $guitar_->{make} == $params{param_make} & $guitar_->{model} eq $params{param_model} & $guitar_->{strings}->includes($params{param_string})

For another working query example, see the sample entity included with the myco base distribution.

Conclusion ^

There's a ton more you can do with myco, though this guide should provide you with a good start. Cheers, and let us know how you like myco!

AUTHOR ^

Ben Sommer <ben@mycohq.com>

SEE ALSO ^

Myco, Myco::Admin

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