DBIx::Class::Manual::IUser(Contributed Perl DocumDBIx::Class::Manual::Intro(3)NAME
DBIx::Class::Manual::Intro - Introduction to DBIx::Class
INTRODUCTION
You're bored with SQL, and want a native Perl interface for your
database? Or you've been doing this for a while with Class::DBI, and
think there's a better way? You've come to the right place.
THE DBIx::Class WAY
Here are a few simple tips that will help you get your bearings with
DBIx::Class.
Tables become Result classes
DBIx::Class needs to know what your Table structure looks like. You do
that by defining Result classes. Result classes are defined by calling
methods proxied to DBIx::Class::ResultSource. Each Result class
defines one Table, which defines the Columns it has, along with any
Relationships it has to other tables. (And oh, so much more besides)
The important thing to understand:
A Result class == Table
(most of the time, but just bear with my simplification)
It's all about the ResultSet
So, we've got some ResultSources defined. Now, we want to actually use
those definitions to help us translate the queries we need into handy
perl objects!
Let's say we defined a ResultSource for an "album" table with three
columns: "albumid", "artist", and "title". Any time we want to query
this table, we'll be creating a DBIx::Class::ResultSet from its
ResultSource. For example, the results of:
SELECT albumid, artist, title FROM album;
Would be retrieved by creating a ResultSet object from the album
table's ResultSource, likely by using the "search" method.
DBIx::Class doesn't limit you to creating only simple ResultSets -- if
you wanted to do something like:
SELECT title FROM album GROUP BY title;
You could easily achieve it.
The important thing to understand:
Any time you would reach for a SQL query in DBI, you are
creating a DBIx::Class::ResultSet.
Search is like "prepare"
DBIx::Class tends to wait until it absolutely must fetch information
from the database. If you are returning a ResultSet, the query won't
execute until you use a method that wants to access the data. (Such as
"next", or "first")
The important thing to understand:
Setting up a ResultSet does not execute the query; retrieving
the data does.
Search results are returned as Rows
Rows of the search from the database are blessed into DBIx::Class::Row
objects.
SETTING UP DBIx::Class
Let's look at how you can set and use your first native DBIx::Class
tree.
First we'll see how you can set up your classes yourself. If you want
them to be auto-discovered, just skip to the next section, which shows
you how to use DBIx::Class::Schema::Loader.
Setting it up manually
First, you should create your base schema class, which inherits from
DBIx::Class::Schema:
package My::Schema;
use base qw/DBIx::Class::Schema/;
In this class you load your result_source ("table", "model") classes,
which we will define later, using the load_namespaces() method:
# load My::Schema::Result::* and their resultset classes
__PACKAGE__->load_namespaces();
By default this loads all the Result (Row) classes in the
My::Schema::Result:: namespace, and also any resultset classes in the
My::Schema::ResultSet:: namespace (if missing, the resultsets are
defaulted to be DBIx::Class::ResultSet objects). You can change the
result and resultset namespaces by using options to the
"load_namespaces" in DBIx::Class::Schema call.
It is also possible to do the same things manually by calling
"load_classes" for the Row classes and defining in those classes any
required resultset classes.
Next, create each of the classes you want to load as specified above:
package My::Schema::Result::Album;
use base qw/DBIx::Class::Core/;
Load any additional components you may need with the load_components()
method, and provide component configuration if required. For example,
if you want automatic row ordering:
__PACKAGE__->load_components(qw/ Ordered /);
__PACKAGE__->position_column('rank');
Ordered will refer to a field called 'position' unless otherwise
directed. Here you are defining the ordering field to be named 'rank'.
(NOTE: Insert errors may occur if you use the Ordered component, but
have not defined a position column or have a 'position' field in your
row.)
Set the table for your class:
__PACKAGE__->table('album');
Add columns to your class:
__PACKAGE__->add_columns(qw/ albumid artist title rank /);
Each column can also be set up with its own accessor, data_type and
other pieces of information that it may be useful to have -- just pass
"add_columns" a hash:
__PACKAGE__->add_columns(albumid =>
{ accessor => 'album',
data_type => 'integer',
size => 16,
is_nullable => 0,
is_auto_increment => 1,
},
artist =>
{ data_type => 'integer',
size => 16,
is_nullable => 0,
},
title =>
{ data_type => 'varchar',
size => 256,
is_nullable => 0,
},
rank =>
{ data_type => 'integer',
size => 16,
is_nullable => 0,
default_value => 0,
}
);
DBIx::Class doesn't directly use most of this data yet, but various
related modules such as HTML::FormHandler::Model::DBIC make use of it.
Also it allows you to create your database tables from your Schema,
instead of the other way around. See "deploy" in DBIx::Class::Schema
for details.
See DBIx::Class::ResultSource for more details of the possible column
attributes.
Accessors are created for each column automatically, so
My::Schema::Result::Album will have albumid() (or album(), when using
the accessor), artist() and title() methods.
Define a primary key for your class:
__PACKAGE__->set_primary_key('albumid');
If you have a multi-column primary key, just pass a list instead:
__PACKAGE__->set_primary_key( qw/ albumid artistid / );
Define this class' relationships with other classes using either
"belongs_to" to describe a column which contains an ID of another
Table, or "has_many" to make a predefined accessor for fetching objects
that contain this Table's foreign key:
# in My::Schema::Result::Artist
__PACKAGE__->has_many('albums', 'My::Schema::Result::Album', 'artist');
See DBIx::Class::Relationship for more information about the various
types of available relationships and how you can design your own.
Using DBIx::Class::Schema::Loader
This module (DBIx::Class::Schema::Loader) is an external module, and
not part of the DBIx::Class distribution. It inspects your database,
and automatically creates classes for all the tables in your schema.
The simplest way to use it is via the dbicdump script from the
DBIx::Class::Schema::Loader distribution. For example:
$ dbicdump -o dump_directory=./lib \
-o components='["InflateColumn::DateTime"]' \
MyApp::Schema dbi:mysql:mydb user pass
If you have a mixed-case database, use the "preserve_case" option,
e.g.:
$ dbicdump -o dump_directory=./lib -o preserve_case=1 \
-o components='["InflateColumn::DateTime"]' \
MyApp::Schema dbi:mysql:mydb user pass
If you are using Catalyst, then you can use the helper that comes with
Catalyst::Model::DBIC::Schema:
$ script/myapp_create.pl model MyDB DBIC::Schema MyDB::Schema \
create=static moniker_map='{ foo => "FOO" }' dbi:SQLite:./myapp.db \
on_connect_do='PRAGMA foreign_keys=ON' quote_char='"'
See Catalyst::Helper::Model::DBIC::Schema for more information on this
helper.
See the DBIx::Class::Schema::Loader and
DBIx::Class::Schema::Loader::Base documentation for more information on
the many loader options.
Connecting
To connect to your Schema, you need to provide the connection details
or a database handle.
Via connection details
The arguments are the same as for "connect" in DBI:
my $schema = My::Schema->connect('dbi:SQLite:/home/me/myapp/my.db');
You can create as many different schema instances as you need. So if
you have a second database you want to access:
my $other_schema = My::Schema->connect( $dsn, $user, $password, $attrs );
Note that DBIx::Class::Schema does not cache connections for you. If
you use multiple connections, you need to do this manually.
To execute some SQL statements on every connect you can add them as an
option in a special fifth argument to connect:
my $another_schema = My::Schema->connect(
$dsn,
$user,
$password,
$attrs,
{ on_connect_do => \@on_connect_sql_statments }
);
See "connect_info" in DBIx::Class::Storage::DBI for more information
about this and other special "connect"-time options.
Via a database handle
The supplied coderef is expected to return a single connected database
handle (e.g. a DBI $dbh)
my $schema = My::Schema->connect (
sub { Some::DBH::Factory->connect },
\%extra_attrs,
);
Basic usage
Once you've defined the basic classes, either manually or using
DBIx::Class::Schema::Loader, you can start interacting with your
database.
To access your database using your $schema object, you can fetch a
"ResultSet" in DBIx::Class::Manual::Glossary representing each of your
tables by calling the "resultset" method.
The simplest way to get a record is by primary key:
my $album = $schema->resultset('Album')->find(14);
This will run a "SELECT" with "albumid = 14" in the "WHERE" clause, and
return an instance of "My::Schema::Result::Album" that represents this
row. Once you have that row, you can access and update columns:
$album->title('Physical Graffiti');
my $title = $album->title; # $title holds 'Physical Graffiti'
If you prefer, you can use the "set_column" and "get_column" accessors
instead:
$album->set_column('title', 'Presence');
$title = $album->get_column('title');
Just like with Class::DBI, you call "update" to save your changes to
the database (by executing the actual "UPDATE" statement):
$album->update;
If needed, you can throw away your local changes:
$album->discard_changes if $album->is_changed;
As you can see, "is_changed" allows you to check if there are local
changes to your object.
Adding and removing rows
To create a new record in the database, you can use the "create"
method. It returns an instance of "My::Schema::Result::Album" that can
be used to access the data in the new record:
my $new_album = $schema->resultset('Album')->create({
title => 'Wish You Were Here',
artist => 'Pink Floyd'
});
Now you can add data to the new record:
$new_album->label('Capitol');
$new_album->year('1975');
$new_album->update;
Likewise, you can remove it from the database:
$new_album->delete;
You can also remove records without retrieving them first, by calling
delete directly on a ResultSet object.
# Delete all of Falco's albums
$schema->resultset('Album')->search({ artist => 'Falco' })->delete;
Finding your objects
DBIx::Class provides a few different ways to retrieve data from your
database. Here's one example:
# Find all of Santana's albums
my $rs = $schema->resultset('Album')->search({ artist => 'Santana' });
In scalar context, as above, "search" returns a DBIx::Class::ResultSet
object. It can be used to peek at the first album returned by the
database:
my $album = $rs->first;
print $album->title;
You can loop over the albums and update each one:
while (my $album = $rs->next) {
print $album->artist . ' - ' . $album->title;
$album->year(2001);
$album->update;
}
Or, you can update them all at once:
$rs->update({ year => 2001 });
In list context, the "search" method returns all of the matching rows:
# Fetch immediately all of Carlos Santana's albums
my @albums = $schema->resultset('Album')->search(
{ artist => 'Carlos Santana' }
);
foreach my $album (@albums) {
print $album->artist . ' - ' . $album->title;
}
We also provide a handy shortcut for doing a "LIKE" search:
# Find albums whose artist starts with 'Jimi'
my $rs = $schema->resultset('Album')->search_like({ artist => 'Jimi%' });
Or you can provide your own "WHERE" clause:
# Find Peter Frampton albums from the year 1986
my $where = 'artist = ? AND year = ?';
my @bind = ( 'Peter Frampton', 1986 );
my $rs = $schema->resultset('Album')->search_literal( $where, @bind );
The preferred way to generate complex queries is to provide a
SQL::Abstract construct to "search":
my $rs = $schema->resultset('Album')->search({
artist => { '!=', 'Janis Joplin' },
year => { '<' => 1980 },
albumid => { '-in' => [ 1, 14, 15, 65, 43 ] }
});
This results in something like the following "WHERE" clause:
WHERE artist != 'Janis Joplin'
AND year < 1980
AND albumid IN (1, 14, 15, 65, 43)
For more examples of complex queries, see
DBIx::Class::Manual::Cookbook.
The search can also be modified by passing another hash with
attributes:
my @albums = My::Schema->resultset('Album')->search(
{ artist => 'Bob Marley' },
{ rows => 2, order_by => { -desc => 'year' } }
);
@albums then holds the two most recent Bob Marley albums.
For more information on what you can do with a DBIx::Class::ResultSet,
see "METHODS" in DBIx::Class::ResultSet.
For a complete overview of the available attributes, see "ATTRIBUTES"
in DBIx::Class::ResultSet.
NOTES
The Significance and Importance of Primary Keys
The concept of a primary key in DBIx::Class warrants special
discussion. The formal definition (which somewhat resembles that of a
classic RDBMS) is a unique constraint that is least likely to change
after initial row creation. However this is where the similarity ends.
Any time you call a CRUD operation on a row (e.g. delete, update,
discard_changes, etc.) DBIx::Class will use the values of of the
primary key columns to populate the "WHERE" clause necessary to
accomplish the operation. This is why it is important to declare a
primary key on all your result sources even if the underlying RDBMS
does not have one. In a pinch one can always declare each row
identifiable by all its columns:
__PACKAGE__->set_primary_key(__PACKAGE__->columns);
Note that DBIx::Class is smart enough to store a copy of the PK values
before any row-object changes take place, so even if you change the
values of PK columns the "WHERE" clause will remain correct.
If you elect not to declare a "primary key", DBIx::Class will behave
correctly by throwing exceptions on any row operation that relies on
unique identifiable rows. If you inherited datasets with multiple
identical rows in them, you can still operate with such sets provided
you only utilize DBIx::Class::ResultSet CRUD methods: search, update,
delete
For example, the following would not work (assuming "People" does not
have a declared PK):
my $row = $schema->resultset('People')
->search({ last_name => 'Dantes' })
->next;
$row->update({ children => 2 }); # <-- exception thrown because $row isn't
# necessarily unique
So instead the following should be done:
$schema->resultset('People')
->search({ last_name => 'Dantes' })
->update({ children => 2 }); # <-- update's ALL Dantes to have children of 2
Problems on RHEL5/CentOS5
There used to be an issue with the system perl on Red Hat Enterprise
Linux 5, some versions of Fedora and derived systems. Further
information on this can be found in
DBIx::Class::Manual::Troubleshooting
SEE ALSO
ยท DBIx::Class::Manual::Cookbook
perl v5.16.2 2012-10-18 DBIx::Class::Manual::Intro(3)
