NAME

DBIx::HTML::LinkedMenus - Convert SQL to 2 linked HTML popup menus.

Synopsis

        use DBIx::HTML::LinkedMenus;
        my($linker) = DBIx::HTML::LinkedMenus -> new
        (
                dbh        => $dbh,
                base_sql   => 'select campus_id, campus_name, campus_id ' .
                                                'from campus order by campus_name',
                linked_sql => 'select unit_id, unit_code from unit where ' .
                                                'unit_campus_id = ? order by unit_code',
        );
        # Print as part of a form:
        print $q -> start_form...
        print $linker -> javascript_for_db();
        print $linker -> html_for_base_menu();
        print $linker -> html_for_linked_menu();
        print $linker -> javascript_for_init_menu(); # Either this...
        print $q -> end_form();
        # Alternately, print as part of a page:
        my(@on_load) = $linker -> javascript_for_on_load(); # Or these 2...
        print $q -> start_html({title => 'Linked Menus', @on_load}),
        print $q -> start_form...
        print $linker -> javascript_for_db();
        print $linker -> html_for_base_menu();
        print $linker -> html_for_linked_menu();
        print $q -> end_form();

Description

This module's constructor takes a db handle and 2 SQL statements, and executes the SQL.

The first SQL statement is used to create a pop-up menu - the base menu.

The constructor returns undef if the SQL for the base menu returns 0 items.

The second SQL statement is used to create another pop-up menu - the linked menu.

By linked I mean each item in the base menu has a corresponding set of items in the linked menu.

Eg: If the available selections on the base menu are A and B, and A is the current selection, then the linked menu will display (say) A1, A2 and A3. Then, when the user changes the current selection on the base menu from A to B, the javascript provided will automatically change the available selections on the linked menu to (say) B1 and B2.

Details of the SQL are explained below.

You use the methods, as above, to retrieve the JavaScript and HTML, and include them in your CGI form.

The JavaScript is in 2 parts:

The data and some general functions
This is returned by the method javascript_for_db().

A function call to initialize the linked-menu system
This is returned by the method javascript_for_init_menu(), or by the method javascript_for_on_load().

This initialization code can be output after the other components of the form, or it can be output as the form's onLoad event handler.

Both ways of doing this are demonstrated in the Synopsis.

Either way, it must be called.

The HTML is also in 2 parts:

The HTML for the base menu
This is returned by the method html_for_base_menu().

As the user of the form changes her selection on the base menu, the available items on the linked menu change in lockstep.

The selections on the base menu are determined by the base_sql parameter.

The HTML for the linked menu
This is returned by the method html_for_linked_menu().

The selections on the linked menu, for each base menu selection, are determined by the linked_sql parameter.

These 2 menus are available separately so you can place them anywhere on your form.

After a call to new, you can call the 'size' method if you need to check how many rows were returned by the base SQL you used.

Neither the module CGI.pm, nor any of that kidney, are used by this module. We simply output pure HTML.

However, for simplicity, this document pretends you are using CGI.pm rather than an alternative. The sentences would become too convoluted otherwise.

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/installing-a-module.html for help on unpacking and installing each type of distro.

Usage

You create an object of the class by calling the constructor, 'new'.

Now call four (4) methods to get the HTML and the JavaScript.

Lastly, display the HTML and JavaScript as part of a form.

Options

Here, in alphabetical order, are the options accepted by the constructor, together with their default values.

base_menu_name => 'dbix_base_menu'
This option is not mandatory, since it has a default value.

The value of this parameter is what you would pass into a CGI object when you call its param() method to retrieve the user's selection on the base menu.

But don't call CGI's param(). Call our get() method, and it will return the base and linked menu selections from the internal hash holding the data.

Examine the demo in the examples/ directory to clarify this process.

base_sql => ''
This option is mandatory.

This is the SQL used to select items for the base menu.

The SQL must select three (3) columns, in this order:

First column
The first column will be used as the value returned by a CGI object, for example, when you call its param(<base_menu_name>) method.

Second column
The second column will be used as the visible selection offered to the user on the base menu.

Third column
The third column will be used as the value plugged into the linked_sql in place of the ? to select a set of items for the linked menu which will correspond to this base menu item.

Of course, the first 2 columns selected could be the same:

        base_sql => 'select campus_name, campus_name, campus_id ' .
                                'from campus order by campus_name'

But normally you would do this:

        base_sql => 'select campus_id, campus_name, campus_id from ' .
                                'campus order by campus_name'

Again: This means that the second column is used to construct visible menu items, and when an item is selected by the user, the first column is what is returned to your CGI script, and the third column is used to select items for the linked menu.

dbh => ''
Pass in an open database handle.

This option is mandatory.

form_name => 'dbix_form'
This option is not mandatory, since it has a default value.

The value of this parameter becomes the name for the form used in the JavaScript, and must be the name used by you in your call to CGI's start_form() or start_multipart_form() method.

linked_menu_name => 'dbix_linked_menu'
This option is not mandatory, since it has a default value.

The value of this parameter is what you would pass into a CGI object when you call its param() method to retrieve the user's selection on the linked menu.

But don't call CGI's param(). Call our get() method, and it will return the base and linked menu selections from the internal hash holding the data.

Examine the demo in the examples/ directory to clarify this process.

linked_sql => ''
This option is mandatory.

This is the SQL used to select items for the linked menu for each selection of the base menu.

The SQL must select two (2) columns, in this order:

First column
The first column will be used as the value returned by a CGI object, for example, when you call its param(<linked_menu_name>) method.

Second column
The second column will be used as the visible selection offered to the user on the linked menu.

Of course, the first 2 columns selected could be the same:

        linked_sql => 'select unit_code, unit_code from unit where ' .
                                'unit_campus_id = ? order by unit_code',

But normally you would do this:

        linked_sql => 'select unit_id, unit_code from unit where ' .
                                'unit_campus_id = ? order by unit_code',

Again: This means that the second column is used to construct visible menu items, and when an item is selected by the user, the first column is what is returned to your CGI script.

Now, notice the where clause. Each value of column three (3) returned by the base_sql is used to select a set of items for the linked menu. The ? in the linked_sql's where clause is where the value from the third column of the base_sql is plugged into the linked_sql.

If a particular value of the base_sql's column three (3) does not return any items for the linked menu, then that basic item does not appear on the base menu.

Methods

get($base_id, $link_id)
Returns the 2 visible menu items, (base, linked), corresponding to the 2 menu selections.

Returns () if either $base_id or $link_id is not a key into the internal hash holding the data.

You would normally do something like this:

        my($base_id) = $q -> param('dbix_base_menu')   || '';
        my($link_id) = $q -> param('dbix_linked_menu') || '';
        my($linker)  = ...
        my(@value)   = $linker -> get($base_id, $link_id);

html_for_base_menu()
Returns the HTML for a popup menu named after the base_menu_name parameter.

Output it somewhere suitable on your page.

Calling this method and outputting the HTML is mandatory.

html_for_linked_menu()
Returns the HTML for a popup menu named after the linked_menu_name parameter.

Output it somewhere suitable on your page.

Calling this method and outputting the HTML is mandatory.

javascript_for_db()
Returns JavaScript, including the <script>...</script> tags, which holds your data in a JavaScript db, and includes some JavaScript functions.

Output it somewhere suitable on your page.

Calling this method and outputting the JavaScript is mandatory.

javascript_for_init_menu()
Returns JavaScript, including the <script>...</script> tags, which holds the function call to a function which initializes the linked-menu system. The function itself is included in the code returned by javascript_for_db().

Output it somewhere on your page after you have output the 2 pieces of HTML and after you have output the string returned from javascript_for_db().

Calling this method is optional. If you do not call it, then calling the method javascript_for_on_load() is mandatory.

javascript_for_on_load()
Returns a string to be used as a <body> tag's onLoad event handler. It calls the function which initializes the linked-menu system. The function itself is included in the code returned by javascript_for_db().

Output it as part of the <body> tag. See examples/test-linked-menus.cgi for an example.

Calling this method is optional. If you do not call it, then calling the method javascript_for_init_menu() is mandatory.

new(%arg)
The constructor.

See the previous section for details of the parameters.

size()
Returns the number of rows returned by your base SQL.

It will tell you whether or not your base menu is empty.

Sample Code

See examples/test-linked-menus.cgi for a complete program.

You will need to run examples/bootstrap-menus.pl to load the 'test' database, 'campus' and 'unit' tables, with sample data.

You'll have to patch these 2 programs vis-a-vis the db vendor, username and password.

The sample data in bootstrap-menus.pl is simple, but is used by several modules, so don't be too keen on changing it :-).

See Also

        CGI::Explorer
        DBIx::HTML::ClientDB
        DBIx::HTML::PopupRadio

Author

DBIx::HTML::LinkedMenus was written by Ron Savage <ron@savage.net.au> in 2002.

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

Copyright

Austrlian copyright (c) 2002, 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