• NAME
• Synopsis
• Description
• Distributions
• Constructor and initialization
• Method: new(...)
• Method: select(%parameter)
• Method: select_hashref(%parameter)
• Method: select_tree(%parameter)
• DBIx::Table2Hash and CGI::Explorer
• Required Modules
• Changes
• FAQ
• Author
• Copyright

NAME

DBIx::Table2Hash - Read a database table into a hash

Synopsis

        #!/usr/bin/perl

        use DBIx::Table2Hash;

        my($key2value) = DBIx::Table2Hash -> new
        (
                dbh           => $dbh,
                table_name    => $table_name,
                key_column    => 'name',
                value_column  => 'id'
        ) -> select();

        # or

        my($key2hashref) = DBIx::Table2Hash -> new
        (
                dbh           => $dbh,
                table_name    => $table_name,
                key_column    => 'name',
        ) -> select_hashref();

        # or

        my($key2tree) = DBIx::Table2Hash -> new
        (
                dbh           => $dbh,
                table_name    => $table_name,
                key_column    => 'name',
                child_column  => 'id',
                parent_column => 'parent_id'
        ) -> select_tree();

Description

DBIx::Table2Hash is a pure Perl module.

This module reads a database table and stores keys and values in a hash.

The aim is to create a hash which is a simple look-up table. To this end, the module allows the key_column to point to an SQL expression.

select() and select_hashref() do not nest the hash in any way.

select_tree() returns a nested hash. select_tree() will call select_hashref() if necessary, ie if you have not called select_hashref() first.

Distributions

This module is available both as a Unix-style distro (*.tgz) and an ActiveState-style distro (*.ppd). The latter is shipped in a *.zip file.

See http://savage.net.au/Perl-modules.html for details.

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

Constructor and initialization

new(...) returns a DBIx::Table2Hash object.

This is the class's contructor.

Parameters:

Note: These parameters are not checked until you call select_*(), which means the parameters can be passed in to new(), select_*(), or both.

dbh

A database handle.

This parameter is mandatory.

table_name

The name of the table to select from.

This parameter is mandatory.

key_column

When calling select(), select_hashref() and select_tree(), this is the name of the database column, or the SQL expression, to use for hash keys.

Say you have 2 columns, called col_a and col_b. Then you can concatenate them with:

key_column => 'concat(col_a, col_b)'

or, even fancier,

key_column => ``concat(col_a, '-', col_b)''

This parameter is mandatory.

child_column

When calling select_tree(), this is the name of the database column which, combined with the parent_column column, defines the relationship between nodes and their children.

This parameter is mandatory if you call select_tree(), and ignored if you call select() or select_hashref().

parent_column

When calling select_tree(), this is the name of the database column which, combined with the child_column column, defines the relationship between nodes and their children.

This parameter is mandatory if you call select_tree(), and ignored if you call select() or select_hashref().

value_column

The name of the database column to use for hash values.

This parameter is mandatory if you call select(), and ignored if you call select_hashref() or select_tree().

where

The optional where clause, including the word 'where', to add to the select.

Method: new(...)

Returns a object of type DBIx::Table2Hash.

See above, in the section called 'Constructor and initialization'.

Method: select(%parameter)

Returns a hash ref.

Each key in the hash points to a single value.

Named parameters, as documented above, can be passed in to this method.

Calling select() actually executes the SQL select statement, and builds the hash.

The demo program test-table2hash.pl, in the examples/ directory, calls select().

Method: select_hashref(%parameter)

Returns a hash ref.

Each key in the hash points to a hashref.

Named parameters, as documented above, can be passed in to this method.

Calling select_hashref() actually executes the SQL select statement, and builds the hash.

The demo program test-table2hash.pl, in the examples/ directory, calls select_hashref().

Method: select_tree(%parameter)

Returns a hash ref.

Each key in the hash points to a hashref.

Named parameters, as documented above, can be passed in to this method.

Calling select_tree() automatically calls select_hashref(), if you have not already called select_hashref().

The demo program test-table2tree.pl, in the examples/ directory, calls select_tree().

DBIx::Table2Hash and CGI::Explorer

The method select_tree() can obviously return a hash with multiple keys at the root level, depending on the contents of the database table.

Such a hash cannot be passed in to CGI::Explorer V 2.00+. Here's a way around this restriction: Create, on the fly, a hash key which is The Mother of All Roots. Eg:

        my($t2h)  = DBIx::Table2Hash -> new(...);
        my($tree) = $t2h -> select_tree(...);
        my($exp)  = CGI::Explorer -> new(...) -> from_hash(hashref => {OneAndOnly => $tree});

Required Modules

Only those shipped with Perl.

Changes

See Changes.txt.

FAQ

Q: What is the point of this module?

A 1: To be able to restore a hash from a database rather than from a file.

A 2: To be able to construct, from a database table, a hash suitable for passing in to CGI::Explorer V 2.00.

Q: Can your other module DBIx::Hash2Table be used to save the hash back to the database?

A: Sure.

Q: Do you ship demos for the 3 methods select(), select_hashref() and select_tree()?

A: Yes. See the examples/ directory.

If you installed this module locally via ppm, look in the x86/ directory for the file to unpack.

If you installed this module remotely via ppm, you need to download and unpack the distro itself.

Q: Are there any other modules with similar capabilities?

A: Yes:

DBIx::Lookup::Field

Quite similar.

DBIx::TableHash

This module takes a very long set of parameters, but unfortunately does not take a database handle.

It does mean the module, being extremely complex, can read in more than one column as the value of a hash key, and it has caching abilities too.

It works by tieing a hash to an MySQL table, and hence supports writing to the table. It uses MySQL-specific code, for example, when it locks tables.

Unfortunately, it does not use data binding, so it cannot handle data which contains single quotes!

Further, it uses /^\w+$/ to 'validate' column names, so it cannot accept an SQL expression instead of a column name.

Lastly, it also uses /^\w+$/ to 'validate' table names, so it cannot accept table names and views containing spaces and other 'funny' characters, eg '&' (both of which I have to deal with under MS Access).

DBIx::Tree

This module was the inspiration for select_tree().

As it reads the database table it calls a call-back sub, which you use to process the rows of the table.

Author

DBIx::Table2Hash was written by Ron Savage <ron@savage.net.au> in 2003.

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

Copyright

Australian copyright (c) 2003, Ron Savage. All rights reserved.

        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:
        http://www.opensource.org/licenses/index.html