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SPOPS-0.75
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/ SPOPS::Manual::Cookbook

NAME

SPOPS::Manual::Cookbook - Recipes for SPOPS usage

DESCRIPTION

This is a collection of recipes for usage of SPOPS. Some are common, some might be esoteric, but all of them should help to illuminate how SPOPS works and ways that you can expand it for your own needs.

DATASOURCE AVAILABILITY

SPOPS implementations that rely on some sort of datasource connection need to make that connection available all objects and class methods that need it. You can also pass a connection around to all calls, but this becomes difficult to maintain and is generally only used for special cases.

All implementations use the method global_datasource_handle() to retrieve the needed connection. So if you make the connection available via this method you never have to pass around handles or even worry about it.

There are generally two ways (which are basically the same) to do this:

  1. Make the handle available via a method in the SPOPS object class itself.

  2. Make the handle available via a method in the ancestor class.

Both are demonstrated below, using the SPOPS::DBI implementation as an example.

Datasource via object class

This method works well if you have a small number of objects, or if you want to something quickly.

Given the configuration:

 1: my $spops = {
 2:   'news' => {
 3:      class           => 'My::News',
 4:      isa             => [ 'SPOPS::DBI::Pg', 'SPOPS::DBI' ],
 5:      rules_from      => [ 'My::DiscoverField' ],
 6:      code_class      => [ 'My::NewsHandle' ],
 7:      field_discover  => 'yes',
 8:      base_table      => 'news',
 9:      id_field        => 'news_id',
10:      increment_field => 1,
11:      no_insert       => [ 'news_id' ],
12:      no_update       => [ 'news_id' ],
13:   },
14: };

We can implement the datasource retrieval via a separate class:

 1: package My::NewsHandle;
 2: 
 3: use strict;
 4: use vars qw( $DBH );
 5: use DBI;
 6: 
 7: $DBH = undef;
 8: 
 9: sub global_datasource_handle {
10:     my ( $class ) = @_;
11:     return $DBH if ( $DBH );
12:     $DBH = DBI->connect( 'DBI:Pg:dbname=mydb', 'postgres', 'postgres',
13:                          { RaiseError => 1, PrintError = 0 } );
14:     unless ( $DBH ) {
15:         die "Cannot create database handle! Error: $DBI::errstr\n";
16:     }
17:     return $DBH;
18: }
19: 
20: 1;

Or we can also use a self-contained script to do it:

 1: #!/usr/bin/perl
 2: 
 3: use strict;
 4: use DBI;
 5: use SPOPS::Initialize;
 6: 
 7: my ( $DBH );
 8: 
 9: {
10:     my $spops = {
11:       'news' => {
12:          class           => 'My::News',
13:          isa             => [ 'SPOPS::DBI::Pg', 'SPOPS::DBI' ],
14:          rules_from      => [ 'My::DiscoverField' ],
15:          code_class      => [ 'My::NewsHandle' ],
16:          field_discover  => 'yes',
17:          base_table      => 'news',
18:          id_field        => 'news_id',
19:          increment_field => 1,
20:          no_insert       => [ 'news_id' ],
21:          no_update       => [ 'news_id' ],
22:       },
23:     };
24: 
25:     SPOPS::Initialize->process({ config => $spops });
26: }
27: 
28: sub My::News::global_datasource_handle {
29:     my ( $class ) = @_;
30:     return $DBH if ( $DBH );
31:     $DBH = DBI->connect( 'DBI:Pg:dbname=mydb', 'postgres', 'postgres',
32:                          { RaiseError => 1, PrintError = 0 } );
33:     unless ( $DBH ) {
34:         die "Cannot create database handle! Error: $DBI::errstr\n";
35:     }
36:     return $DBH;
37: }

Datasource via ancestor class

If you're using a lot of objects that share the same database or get their connection parameters from a common location, creating a common ancestor class is usually a better way to go.

First create an ancestor class with the global_datasource_handle() method:

 1: package MyApp::Datasource; # -*-perl-*-
 2: 
 3: use strict;
 4: use DBI;
 5: 
 6: my ( $DBH );
 7: 
 8: sub global_datasource_handle {
 9:     my ( $class ) = @_;
10:     return $DBH if ( $DBH );
11:     $DBH = DBI->connect( 'DBI:Pg:dbname=mydb', 'postgres', 'postgres',
12:                          { RaiseError => 1, PrintError = 0 } );
13:     unless ( $DBH ) {
14:         die "Cannot create database handle! Error: $DBI::errstr\n";
15:     }
16:     return $DBH;
17: }
18: 
19: 1;

And then include the ancestor class in the 'isa' key of your object's configuration:

 1: my $spops = {
 2:   'news' => {
 3:      class           => 'My::News',
 4:      isa             => [ qw/ MyApp::Datasource SPOPS::DBI::Pg SPOPS::DBI / ],
 5:      rules_from      => [ 'My::DiscoverField' ],
 6:      code_class      => [],
 7:      field_discover  => 'yes',
 8:      base_table      => 'news',
 9:      id_field        => 'news_id',
10:      increment_field => 1,
11:      no_insert       => [ 'news_id' ],
12:      no_update       => [ 'news_id' ],
13:   },
14: };

Then just use as normal.

COMMON QUERIES

A common way to access data is to put a standard library of queries in one place and allow only those queries to be executed.

To create a common query, even one that joins multiple tables, just write a method and put it in a 'code_class'. For our example, we'll use the following configuration:

 1: my $spops = {
 2:   'news' => {
 3:      class           => 'My::News',
 4:      isa             => [ 'SPOPS::DBI::Pg', 'SPOPS::DBI' ],
 5:      rules_from      => [ 'My::DiscoverField' ],
 6:      code_class      => [ 'My::NewsProcs' ],
 7:      field_discover  => 'yes',
 8:      base_table      => 'news',
 9:      id_field        => 'news_id',
10:      increment_field => 1,
11:      no_insert       => [ 'news_id' ],
12:      no_update       => [ 'news_id' ],
13:   },
14: };

And the following code class:

 1: package My::NewsProcs; # -*-perl-*-
 2: 
 3: use strict;
 4: 
 5: # All active news stories by a particular user, sorted in reverse
 6: # date (latest first) order
 7: 
 8: sub by_user {
 9:     my ( $class, $user, $params ) = @_;
10:     unless ( $user->id ) {
11:         SPOPS::Error->set({
12:            error_msg => 'Cannot fetch news messages with unsaved user!',
13:            type      => 'news' });
14:         die $SPOPS::Error::error_msg;
15:     }
16: 
17:     my $iter = eval { $class->fetch_iterator({
18:                                    where => "active = ? AND posted_by = ?",
19:                                    value => [ 'yes', $user->id ],
20:                                    order => 'posted_on DESC',
21:                                    limit => $params->{limit} });
22:     if ( $@ ) {
23:         SPOPS::Error->set({ 
24:            error_msg  => 'Cannot run query to retrieve news messages by user',
25:            system_msg => $SPOPS::Error::system_msg,
26:            type       => 'news' });
27:         die $SPOPS::Error::error_msg;
28:     }
29:     return $iter;    
30: }
31: 
32: 1;

And you would use this like:

 1: #!/usr/bin/perl
 2: 
 3: use strict;
 4: use SPOPS::Initialize;
 5: 
 6: {
 7:     SPOPS::Initialize->process({ filename => 'news_config.perl' });
 8:     my $user = MyApp->current_login;
 9:     my $news_iter = My::News->by_user( $user );
10: 
11:     print "Stories posted by $user->{login_name}:\n";
12:     while ( my $news = $news_iter->get_next ) {
13:         print "$news->{title} posted on $news->{posted_on}\n";
14:     }
15: }

COPYRIGHT

Copyright (c) 2001-2002 Chris Winters. All rights reserved.

See SPOPS::Manual for license.

AUTHORS

Chris Winters <chris@cwinters.com>