Tangram::Dialect - support for SQL dialects and extensions
package Tangram::Dialect::SomeDialect; use Tangram::Dialect; use base qw( Tangram::Dialect ); sub expr { ... }
Like Charles Moore (inventor of Forth) used to say, "standards are great, everybody should have one!".
Tangram can take advantage of extensions available in some SQL dialects. Each Storage has an associated Dialect object. The instantiation of some classes (currently Expr) is delegated to the Dialect object, which may return objects with extended functionality.
Returns a new Dialect object.
Returns a new Expr object. The object is obtained by calling method expr() on $type. See Tangram::Expr for a description of the arguments.
The following code adds support for Sybase's datepart extension. See below how to actually use the extension.
datepart
use strict; ############################################ # derive a DateExpr class from existing Expr package Tangram::Dialect::Sybase::DateExpr; use base qw( Tangram::Expr ); ############################ # add method datepart($part) sub datepart { my ($self, $part) = @_; # $part is 'year', 'month', etc my $expr = $self->expr(); # the SQL string for this Expr ################################## # build a new Expr of Integer type # pass this Expr's remote object list to the new Expr return Tangram::Integer->expr("DATEPART($part, $expr)", $self->objects); } ########################### # subclass Tangram::Dialect package Tangram::Dialect::Sybase; use Tangram::Dialect; use base qw( Tangram::Dialect ); ############################################ # a hash that maps date-related Types to the # DateExpr - the improved Expr class my %improved = ( 'Tangram::RawDateTime' => 'Tangram::Dialect::Sybase::DateExpr', 'Tangram::RawDate' => 'Tangram::Dialect::Sybase::DateExpr', ); ###################################################### # Tangram calls this method to obtain new Expr objects sub expr { my ($self, $type, $expr, @remotes) = @_; ################################################### # is $type related to dates? if not, return default my $improved = $improved{ref($type)} or return $type->expr(@_); #################################### # $type is a Date; return a DateExpr return $improved->new($type, $expr, @remotes); } 1;
To take advantage of the new Dialect, we must pass it to the connect() method:
my $storage = Tangram::Storage->connect($schema, $data_source, $user, $passwd, { dialect => 'Tangram::Dialect::Sybase' } );
Now we can filter on the various parts of a Date:
my $remote = $storage->remote('NaturalPerson'); my ($person) = $storage->select($remote, $remote->{birth}->datepart('year') == 1963);
Tangram::Type, Tangram::Expr, Tangram::Storage.
To install Tangram, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Tangram
CPAN shell
perl -MCPAN -e shell install Tangram
For more information on module installation, please visit the detailed CPAN module installation guide.