# PODNAME: Meerkat::Tutorial
# ABSTRACT: Getting started with Meerkat



=encoding UTF-8

=head1 NAME

Meerkat::Tutorial - Getting started with Meerkat

=head1 VERSION

version 0.015


=head2 Prerequisites

If you don't already have MongoDB installed and running, see the
L<installation guide|http://docs.mongodb.org/manual/installation/>.

Check that you can connect to the C<test> database from the C<mongo> shell:

    $ mongo test

=head2 Creating Your Document Model

A Meerkat document is just a Moose class with the
L<Meerkat::Role::Document> role applied.  This tutorial uses a simplified
version of the C<My::Model::Person> class used for testing.  It has a
required C<name> attribute, and also attributes for C<likes> and C<tags>:

    package My::Model::Person;

    use Moose;

    with 'Meerkat::Role::Document';

    has name => (
        is       => 'ro',
        isa      => 'Str',
        required => 1,

    has likes => (
        is      => 'ro',
        isa     => 'Num',
        default => 0,

    has tags => (
        is      => 'ro',
        isa     => 'ArrayRef',
        default => sub { [] },


Meerkat::Role::Document will also add C<_id>, C<_collection> and
C<_removed> attributes.

Note that all attributes are B<read-only>.  You don't want to modify these
directly or you'll be out of sync with the database and bad things will happen.
You will update attributes using the C<update> methods, shown later.

=head2 Connecting to the Database

Once the document class is written, using it requires a L<Meerkat> object
to manage the connection to the database:

    use Meerkat;

    my $meerkat = Meerkat->new(
        model_namespace => "My::Model",
        database_name   => "test",

By specifying a C<model_namespace> of "My::Model", the object will return
collections for classes underneath that namespace.  The example above will
connect to the default MongoDB on localhost.  If your MongoDB is running on
a different host or port, you could pass C<client_options> which will be
passed through to the L<MongoDB::MongoClient> constructor.

Actually working with the document class requires getting a
L<Meerkat::Collection> object from the Meerkat object.  A Meerkat collection
associates a Perl class name with a specific MongoDB collection in the database
managed by the Meerkat object.

    my $person = $meerkat->collection("Person"); # My::Model::Person

The collection name is derived from the Perl class by replacing "::" with "_".
So "My::Model::Person" objects are stored in the "My_Model_Person" collection.
In this tutorial example, that collection is in the "test" database on the
localhost MongoDB.

=head2 Creating New Documents

A Meerkat document needs to know what collection it came from, so the
Meerkat::Collection is a factory for constructing objects.

    my $obj = $person->create( name => "Larry Wall" );

When the object is created, it is immediately inserted into the database.
(If an error occurs, an exception is thrown.)

Don't create objects directly from the document class.  Even if you provide a
Meerkat::Collection, the documents won't be inserted and things will never get
in sync.  B<Always create objects from a Meerkat::Collection>.

=head2 Updating, Synchronizing and Removing Documents

With Meerkat, objects reflect the state of a document in the database at a
moment in time.  Therefore, you never change the state of your object
directly, because it might no longer reflect the true state of the document
in the database.  Instead, you issue database commands to modify the
document atomically in the database and then Meerkat synchronizes your
object with the result.

Conveniently, Meerkat::Role::Document gives your model class some methods to
make that easy:

    $obj->update_set ( name  => "Warry Lall"   ); # change a field
    $obj->update_inc ( likes => 1              ); # increment a counter
    $obj->update_push( tags  => qw/hot trendy/ ); # push to an array

If you aren't changing data, but want to update your object's snapshot of the
document in the database, call the C<sync> method:


And should you need to get rid of a document, the C<remove> method will take
care of it.


Afterwards, C<is_removed> will be true and C<update> and C<sync> calls will
do nothing and return a false value.

=head2 Errors

Generally, Meerkat methods return true if they executed successfully and false
if they could not.

For example, if a document was removed in the database by another process and
an C<update> or C<sync> is called, it will return false.  (It will flag the
object as having been removed from the database, but will not otherwise modify
its data.)

Should any major error occur, an exception will get thrown.

=head2 Searching the Database

To retrieve a document from the database, the collection provides search
methods similar to L<MongoDB::Collection>, but which return objects from
your model class.

For single objects, there are the C<find_id> and C<find_one> methods:

    # find a single object
    my $obj1 = $person->find_id( $id );
    my $obj2 = $person->find_one( { name => 'John' } );

If you have a L<MongoDB
query|http://docs.mongodb.org/manual/tutorial/query-documents/> for multiple
objects, you pass it to C<find> and get a L<Meerkat::Cursor> object back.  It
proxies for L<MongoDB::Cursor> but returns objects when iterated.

    my $cursor = $person->find( $query_hashref );

    while ( my $obj = $cursor->next ) { ... }

=head2 Next steps

Try out the example class above using the 'test' database on your

Afterwards, check out the L<Meerkat::Cookbook> for more on working with

=head1 AUTHOR

David Golden <dagolden@cpan.org>


This software is Copyright (c) 2013 by David Golden.

This is free software, licensed under:

  The Apache License, Version 2.0, January 2004