DBIx::DataModel - Classes and UML-style Associations on top of DBI
Declare the schema, which automatically creates a Perl package.
# do NOT declare here "package MySchema;"
use DBIx::DataModel;
DBIx::DataModel->Schema('MySchema'); # 'MySchema' is now a Perl package
Declare the tables with (Perl name, DB name, primary key column(s)). Each table then becomes a Perl package (prefixed with the Schema name).
MySchema->Table(qw/Employee Employee emp_id/)
->Table(qw/Department Department dpt_id/)
->Table(qw/Activity Activity act_id/);
Declare associations or compositions in UML style ( [table1 role1 multiplicity1 join1], [table2...]).
MySchema->Composition([qw/Employee employee 1 /],
[qw/Activity activities * /])
->Association([qw/Department department 1 /],
[qw/Activity activities * /]);
Declare a n-to-n association, on top of the linking table
MySchema->Association([qw/Department departments * activities department/]);
[qw/Employee employees * activities employee/]);
Declare "column types" with some handlers ..
# date conversion between database (yyyy-mm-dd) and user (dd.mm.yyyy)
MySchema->ColumnType(Date =>
fromDB => sub {$_[0] =~ s/(\d\d\d\d)-(\d\d)-(\d\d)/$3.$2.$1/},
toDB => sub {$_[0] =~ s/(\d\d)\.(\d\d)\.(\d\d\d\d)/$3-$2-$1/},
validate => sub {$_[0] =~ m/(\d\d)\.(\d\d)\.(\d\d\d\d)/});
# 'percent' conversion between database (0.8) and user (80)
MySchema->ColumnType(Percent =>
fromDB => sub {$_[0] *= 100 if $_[0]},
toDB => sub {$_[0] /= 100 if $_[0]},
validate => sub {$_[0] =~ /1?\d?\d/});
MySchema->ColumnType(Multivalue =>
fromDB => sub {$_[0] = [split /;/, $_[0] || ""] },
toDB => sub {$_[0] = join ";", @$_[0] if ref $_[0]});
.. and apply these "column types" to some of our columns
MySchema::Employee->ColumnType(Date => qw/d_birth/);
MySchema::Activity->ColumnType(Date => qw/d_begin d_end/)
->ColumnType(Percent => qw/activity_rate/);
Declare a column that will be filled automatically at each update
MySchema->AutoUpdateColumns(last_modif =>
sub{$ENV{REMOTE_USER}.", ".scalar(localtime)});
Declare a column that will be not be sent when updating records (for example if that column is filled automatically by the database)
MySchema->NoUpdateColumns(qw/date_modif time_modif/);
For details that could not be expressed in a declarative way, just add a new method into the table class (but in that case, Schema and Table declarations should be in a BEGIN block, so that the table class is defined before you start adding methods to it).
package MySchema::Activity;
sub activePeriod {
my $self = shift;
$self->{d_end} ? "from $self->{d_begin} to $self->{d_end}"
: "since $self->{d_begin}";
}
Declare how to automatically expand objects into data trees
MySchema::Activity->AutoExpand(qw/employee department/);
perl -MDBIx::DataModel::Schema::Generator \
-e "fromDBI('dbi:connection:string')" -- \
-schema My::New::Schema > My/New/Schema.pm
See DBIx::DataModel::Schema::Generator.
use MySchema; use DBI; my $dbh = DBI->connect($dsn, ...); MySchema->dbh($dbh);
Search employees whose name starts with 'D' (select API is taken from SQL::Abstract)
my $empl_D
= MySchema::Employee->select(-where => {lastname => {-like => 'D%'}});
idem, but we just want a subset of the columns, and order by age.
my $empl_F
= MySchema::Employee->select(
-columns => [qw/firstname lastname d_birth/],
-where => {lastname => {-like => 'F%'}},
-orderBy => 'd_birth');
Print some info from employees. Because of the 'fromDB' handler associated with column type 'date', column 'd_birth' has been automatically converted to display format.
foreach my $emp (@$empl_D) {
print "$emp->{firstname} $emp->{lastname}, born $emp->{d_birth}\n";
}
Same thing, but using method calls instead of direct access to the hashref (must enable AUTOLOAD in the table or the whole schema)
MySchema::Employee->Autoload(1); # or MySchema->Autoload(1)
foreach my $emp (@$empl_D) {
printf "%s %s, born %s\n", $emp->firstname, $emp->lastname, $emp->d_birth;
}
Follow the joins through role methods
foreach my $act (@{$emp->activities}) {
printf "working for %s from $act->{d_begin} to $act->{d_end}",
$act->department->name;
}
Role methods can take arguments too, like select()
my $recentAct
= $dpt->activities(-where => {d_begin => {'>=' => '2005-01-01'}});
my @recentEmpl
= map {$_->employee(-columns => [qw/firstname lastname/])} @$recentAct;
Export the data : get related records and insert them into a data tree in memory; then remove all class information and export that tree.
$_->expand('activities') foreach @$empl_D;
my $export = MySchema->unbless({employees => $empl_D});
use Data::Dumper; print Dumper ($export); # export as PerlDump
use XML::Simple; print XMLout ($export); # export as XML
use JSON; print to_json($export); # export as Javascript
use YAML; print Dump ($export); # export as YAML
Note: the unbless step is optional; it is proposed here because some exporter modules will not work if they encounter a blessed reference.
Select associated tables directly from a database join, in one single SQL statement (instead of iterating through role methods).
my $lst = MySchema->join(qw/Employee activities department/)
->select(-columns => [qw/lastname dept_name d_begin/],
-where => {d_begin => {'>=' => '2000-01-01'}});
Same thing, but forcing INNER joins
my $lst = MySchema->join(qw/Employee <=> activities <=> department/)
->select(...);
Instead of retrieving directly a list or records, get a statement :
my $statement
= MySchema->join(qw/Employee activities department/)
->select(-columns => [qw/lastname dept_name d_begin/],
-where => {d_begin => {'>=' => '2000-01-01'}},
-resultAs => 'statement');
Retrieve a single row from the statement
my $single_row = $statement->next or die "no more records";
Retrieve several rows at once
my $rows = $statement->next(10); # arrayref
Go to a specific page and retrieve the corresponding rows
my $statement
= MySchema->join(qw/Employee activities department/)
->select(-columns => [qw/lastname dept_name d_begin/],
-resultAs => 'statement',
-pageSize => 10);
$statement->gotoPage(3); # absolute page positioning
$statement->shiftPages(-2); # relative page positioning
my ($first, $last) = $statement->pageBoundaries;
print "displaying rows $first to $last:";
some_print_row_method($_) foreach @{$statement->pageRows};
For fetching related rows : prepare a statement before the loop, execute it at each iteration.
my $statement = My::Table->join(qw/role1 role2/)
->prepare(-columns => ...,
-where => ...);
my $list = My::Table->select(...);
foreach my $obj (@$list) {
my $related_rows = $statement->execute($obj)->all;
...
}
Fast statement : each data row is retrieved into the same memory location (avoids the overhead of allocating a hashref for each row). Faster, but such rows cannot be accumulated into an array (they must be used immediately) :
my $fast_stmt = ..->select(..., -resultAs => "fast_statement");
while (my $row = $fast_stmt->next) {
do_something_immediately_with($row);
}
DBIx::DataModel is a framework for building Perl abstractions (classes, objects and methods) that interact with relational database management systems (RDBMS). Of course the ubiquitous DBI module is used as a basic layer for communicating with databases; on top of that, DBIx::DataModel provides facilities for generating SQL queries, joining tables automatically, navigating through the results, converting values, and building complex datastructures so that other modules can conveniently exploit the data.
There are many other CPAN modules offering somewhat similar features, like Class::DBI, DBIx::Class, Tangram, Rose::DB::Object, Jifty::DBI, Fey::ORM, just to name a few well-known alternatives. Frameworks in this family are called object-relational mappings (ORMs) -- see http://en.wikipedia.org/wiki/Object-relational_mapping. The mere fact that Perl ORMs are so numerous demonstrates that there is more than one way to do it!
For various reasons, none of these did fit nicely in my context, so I decided to write DBIx:DataModel. Of course there might be also some reasons why DBIx:DataModel will not fit in your context, so just do your own shopping. Comparing various ORMs is complex and time-consuming, because of the many issues and design dimensions involved; as far as I know, there is no thorough comparison summary, but here are some pointers :
DBIx::DataModelThe DESIGN chapter of this documentation will help you understand the philosophy of DBIx::DataModel. Just as a summary, here are some of its strong points :
DBIx::DataModel is used in production within a mission-critical application with several hundred users, for managing Geneva courts of law.
Here are some current limitations of DBIx::DataModel :
DBIx::DataModel knows very little about the database schema (only tables, primary and foreign keys); therefore it provides no support for schema changes (and seldom needs to know about them).
DBIx::DataModel does not keep track of data mutations in memory, and therefore provides no support for automatically propagating changes into the database; the client code has explicitly manage insert and update operations.
Cascaded inserts and deletes are supported, but not cascaded updates. This would need 'insert or create', which at the moment is not supported either.
Although the basic principles are quite simple, there are many details to discuss, so the documentation is quite long. In an attempt to accomodate for different needs of readers, it has been structured as follows :
DBIx::DataModel, its main distinctive features and the motivation for such features; it is of interest if you are comparing various ORMs, or if you want to globally understand how DBIx::DataModel works, and what it can or cannot do. This chapter also details the concept of statements, which underlies all SELECT requests to the database.DBI connection, from a SQL::Translator description or from an existing DBIx::Class|DBIx::Class schema.Upon loading, DBIx::DataModel::View adds a coderef into global @INC (see "require" in perlfunc), so that it can take control and generate a class on the fly when retrieving frozen objects from "thaw" in Storable. This should be totally harmless unless you do some very special things with @INC.
Laurent Dami, <laurent.dami AT etat geneve ch>
Thanks to Cedric Bouvier for some bug fixes and improvements.
Copyright 2006, 2008 by Laurent Dami.
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
