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Ron Savage


GraphViz2::DBI - Visualize a database schema as a graph


        #!/usr/bin/env perl

        use strict;
        use warnings;

        use DBI;

        use GraphViz2;
        use GraphViz2::DBI;

        use Log::Handler;

        # ---------------

        exit 0 if (! $ENV{DBI_DSN});

        my($logger) = Log::Handler -> new;

        $logger -> add
                 screen =>
                         maxlevel       => 'debug',
                         message_layout => '%m',
                         minlevel       => 'error',

        my($graph) = GraphViz2 -> new
                 edge   => {color => 'grey'},
                 global => {directed => 1},
                 graph  => {rankdir => 'TB'},
                 logger => $logger,
                 node   => {color => 'blue', shape => 'oval'},
        my($attr)              = {};
        $$attr{sqlite_unicode} = 1 if ($ENV{DBI_DSN} =~ /SQLite/i);
        my($dbh)               = DBI -> connect($ENV{DBI_DSN}, $ENV{DBI_USER}, $ENV{DBI_PASS}, $attr);

        $dbh -> do('PRAGMA foreign_keys = ON') if ($ENV{DBI_DSN} =~ /SQLite/i);

        my($g) = GraphViz2::DBI -> new(dbh => $dbh, graph => $graph);

        $g -> create(name => '');

        my($format)      = shift || 'svg';
        my($output_file) = shift || File::Spec -> catfile('html', "dbi.schema.$format");

        $graph -> run(format => $format, output_file => $output_file);

See scripts/dbi.schema.pl ("Scripts Shipped with this Module" in GraphViz2).

The image html/dbi.schema.svg was generated from the database tables of my module App::Office::Contacts.


Takes a database handle, and graphs the schema.

You can write the result in any format supported by Graphviz.

Here is the list of output formats.


This module is available as a Unix-style distro (*.tgz).

See http://savage.net.au/Perl-modules/html/installing-a-module.html for help on unpacking and installing distros.


Install GraphViz2 as you would for any Perl module:


        cpanm GraphViz2

or run:

        sudo cpan GraphViz2

or unpack the distro, and then either:

        perl Build.PL
        ./Build test
        sudo ./Build install


        perl Makefile.PL
        make (or dmake or nmake)
        make test
        make install

Constructor and Initialization

Calling new()

new() is called as my($obj) = GraphViz2::DBI -> new(k1 => v1, k2 => v2, ...).

It returns a new object of type GraphViz2::DBI.

Key-value pairs accepted in the parameter list:

o dbh => $dbh

This options specifies the database handle to use.

This key is mandatory.

o graph => $graphviz_object

This option specifies the GraphViz2 object to use. This allows you to configure it as desired.

The default is GraphViz2 -> new. The default attributes are the same as in the synopsis, above, except for the graph label of course.

This key is optional.


create(exclude => [], include => [], name => $name)

Creates the graph, which is accessible via the graph() method, or via the graph object you passed to new().

Returns $self to allow method chaining.


o exclude

An optional arrayref of table names to exclude.

If none are listed for exclusion, all tables are included.

o include

An optional arrayref of table names to include.

If none are listed for inclusion, all tables are included.

o name

$name is the string which will be placed in the root node of the tree. It may be omitted, in which case the root node is omitted.


Returns the graph object, either the one supplied to new() or the one created during the call to new().


Why did I get an error about 'Unable to find primary key'?

For plotting foreign keys, the code has an algorithm to find the primary table/key pair which the foreign table/key pair point to.

The steps are listed here, in the order they are tested. The first match stops the search.

o Check a hash for special cases

Currently, the only special case is a foreign key of spouse_id. It is assumed to point to a primary key called person_id.

There is no option available, at the moment, to override this check.

o Ask the database for foreign key information

DBIx::Admin::TableInfo is used for this.

o Take a guess

Assume the foreign key points to a table with a column called id, and use that as the primary key.

o Die with a detailed error message

Which versions of the servers did you test?

See "FAQ" in DBIx::Admin::TableInfo.

Does GraphViz2::DBI work with SQLite databases?

Yes. See "FAQ" in DBIx::Admin::TableInfo.

What is returned by SQLite's "pragma foreign_key_list($table_name)"?

See "FAQ" in DBIx::Admin::TableInfo.

How does GraphViz2::DBI draw edges from foreign keys to primary keys?

It assumes that the primary table's name is a plural word, and that the foreign key's name is prefixed by the singular of the primary table's name, separated by '_'.

Thus a (primary) table 'people' with a primary key 'id' will be pointed to by a table 'phone_numbers' using a column 'person_id'.

Table 'phone_numbers' will probably have a primary key 'id' but that is not used (unless some other table has a foreign key pointing to the 'phone_numbers' table).

The conversion of plural to singular is done with Lingua::EN::PluralToSingular.

If this naming convention does not hold, then both the source and destination ports default to '1', which is the port of the 1st column (in alphabetical order) in each table. The table name itself is port '0'.

Are any sample scripts shipped with this module?

Yes. See "FAQ" in GraphViz2 and "Scripts Shipped with this Module" in GraphViz2.


Many thanks to the people who chose to make Graphviz Open Source.

And thanks to Leon Brocard, who wrote GraphViz, and kindly gave me co-maint of the module.

Version Numbers

Version numbers < 1.00 represent development versions. From 1.00 up, they are production versions.

Machine-Readable Change Log

The file CHANGES was converted into Changelog.ini by Module::Metadata::Changes.


Email the author, or log a bug on RT:



GraphViz2 was written by Ron Savage <ron@savage.net.au> in 2011.

Home page: http://savage.net.au/index.html.


Australian copyright (c) 2011, Ron Savage.

        All Programs of mine are 'OSI Certified Open Source Software';
        you can redistribute them and/or modify them under the terms of
        The Artistic License, a copy of which is available at: