There goes 1.4.

[maypole.git] / doc / BuySpy.pod

=head1 The Maypole iBuySpy Portal

I think it's good fun to compare Maypole

We begin with a length process of planning and investigating the
sources. Of prime interest is the database schema and the initial data,
which we convert to a Mysql database. Converting MS SQL to Mysql is not fun.
I shall spare you the gore. Especially the bit where the default insert IDs
didn't match up between the tables.

The C<ibsportal> database has a number of tables which describe how the
portal should look, and some tables which describe the data that should
appear on it. The portal is defined in terms of a set of modules; each
module takes some data from somewhere, and specifies a template to be
used to format the data. This is quite different from how Maypole
normally operates, so we have a choice as to whether we're going to
completely copy this design, or use a more "natural" implementation in 
terms of having the portal display defined as a template itself, with
all the modules specified right there in Template Toolkit code rather
than picked up from the database. This would be much faster, since you
get one shot of rendering instead of having to process each module's
template independently. The thing is, I feel like showing off
precisely how flexible Maypole is, so we'll do it the hard way.

The first thing we need to do is get the database into some sort of
useful shape, and work out the relationships between the tables. This of
course requires half a day of playing with GraphViz, Omnigraffle and
mysql, but ended up with something like this:

=for html
<img src="ibs-schema.png">

This leads naturally to the following driver code:

    package Portal;
    use base 'Apache::MVC';
    Portal->setup("dbi:mysql:ibsportal");
    use Class::DBI::Loader::Relationship;
    Portal->config->{loader}->relationship($_) for (
        "A module has a definition",  "A module has settings",
        "A tab has modules",          "A portal has tabs",
        "A role has a portal",        "A definition has a portal",
        "A module has announcements", "A module has contacts",
        "A module has discussions",   "A module has events",
        "A module has htmltexts",     "A module has links",
        "A module has documents",
        "A user has roles via userrole"
    );
    1;

As you can see, a portal is made up of a number of different tabs;
the tabs contain modules, but they're separated into different panes,
so a module knows whether it belongs on the left pane, the right pane
or the center. A module also knows where it appears in the pane.

We'll begin by mocking up the portal view in plain text, like so:

    use Portal;
    my $portal = Portal::Portal->retrieve(2);
    for my $tab ($portal->tabs) {
        print $tab,"\n";
        for my $pane (qw(LeftPane ContentPane RightPane)) {
            print "\t$pane:\n";
            for (sort { $a->module_order <=> $b->module_order }
                $tab->modules(pane => $pane)) {
                print "\t\t$_:\t", $_->definition,"\n";
            }
        }
        print "\n";
    }

This dumps out the tabs of our portal, along with the modules in each
tab and their types; this lets us check that we've got the database
set up properly. If we have, it should produce something like this:

    Home
            LeftPane:
                    Quick link:     Quicklink
            ContentPane:
                    Welcome to the IBuySpy Portal:  Html Document
                    News and Features:      announcement
                    Upcoming event: event
            RightPane:
                    This Week's Special:    Html Document
                    Top Movers:     XML/XSL

    ...

Now we want to get the front page up; for the moment, we'll just have it
display the module names and their definitions like our text mock-up,
and we'll flesh out the actual modules later.

But before we do that, we'll write a front-end URL handler method, to
allow us to ape the ASP file names. Why do we want to make a Maypole
site look like it's running C<.aspx> files? Because we can! - and
because I want to show we don't necessarily B<have> to follow the
Maypole tradition of having our URLs look like
C</I<table>/I<action>/I<id>/I<arguments>>. 

    our %pages = (
        "DesktopDefault.aspx" => { action => "view", table => "tab" },
        "MobileDefault.aspx"  => { action => "view_mobile", table => "tab" },
    );

    sub parse_path {
        my $self = shift;
        $self->{path} ||= "DesktopDefault.aspx";
        return $self->SUPER::parse_path if not exists $pages{$self->{path}};
        my $page = $pages{$self->{path}} ;
        $self->{action} = $page->{action};
        $self->{table} = $page->{table};
        my %query = $self->{ar}->args;
        $self->{args} = [ $query{tabid} || $query{ItemID} || 1];
    }

    1;

Here we're overriding the C<parse_path> method which takes the C<path>
slot from the request and populates the C<table>, C<action> and
C<arguments> slots. If the user has asked for a page we don't know
about, we ask the usual Maypole path handling method to give it a try;
this will become important later on. We turn the default page,
C<DesktopDefault.aspx>, into the equivalent of C</tab/view/1> unless
another C<tabid> or C<ItemID> is given in the query parameters; this allows us
to use the ASP.NET-style C<DesktopDefault.aspx?tabid=3> to select a tab.

Now we have to create our C<tab/view> template; the majority of
this is copied from the F<DesktopDefault.aspx> source, but our panes
look like this:

    <td id="LeftPane" Width="170">
        [% pane("LeftPane") %]
    </td>
    <td width="1">
    </td>
    <td id="ContentPane" Width="*">
        [% pane("ContentPane") %]
    </td>
    <td id="RightPane" Width="230">
        [% pane("RightPane") %]
    </td>
    <td width="10">
        &nbsp;
   </td>

The C<pane> macro has to be the Template Toolkit analogue of the Perl code
we used for our mock-up:

    [% MACRO pane(panename) BLOCK;
        FOR module = tab.modules("pane", panename);
            "<P>"; module; " - "; module.definition; "</P>";
        END;
    END;

Now, the way that the iBuySpy portal works is that each module has a
definition, and each definition contains a path to a template:
C<$module-E<gt>definition-E<gt>DesktopSrc> returns a path name for an C<ascx>
component file. All we need to do is convert those files from ASP to the
Template Toolkit, and have Maypole process each component for each module,
right?

=head2 Components and templates

Dead right, but it was here that I got too clever. I guess it was the word
"component" that set me off. I thought that since the page was made up of a
large number of different modules, all requiring their own set of objects, I
should use a seperate Maypole sub-request for each one, as shown in the
"Component-based pages" recipe in L<Request.pod>.

So this is what I did. I created a method in C<Portal::Module> that would
set the template to the appropriate C<ascx> file:

    sub view_desktop :Exported {
        my ($self, $r) = @_;
        $r->{template} = $r->objects->[0]->definition->DesktopSrc;
    }

and changed the C<pane> macro to fire off a sub-request for each module:

    [% MACRO pane(panename) BLOCK;
        FOR module = tab.modules("pane", panename);
            SET path = "/module/view_desktop/" _ module.id;
            request.component(path);
        END;
    END; %]

This did the right thing, and a call to C</module/view_desktop/12> would
look up the C<Html Document> module definition, find the C<DesktopSrc> to
be F<DesktopModules/HtmlModule.ascx>, and process module 12 with that
template. Once I had converted F<HtmlModule.ascx> to be a Template Toolkit
file (and we'll look at the conversion of the templates in a second) it
would display nicely on my portal.

Except it was all very slow; we were firing off a large number of Maypole
requests in series, so that each template could get at the objects it
needed. Requests were taking 5 seconds.

That's when it dawned on me that these templates don't actually need different
objects at all. The only object of interest that C</module/view_desktop> is
passing in is a C<module> object, and each template figures everything out by
accessor calls on that. But we already have a C<module> object, in our C<FOR>
loop - we're using it to make the component call, after all! Why not just
C<PROCESS> each template inside the loop directly?

    [% MACRO pane(panename) BLOCK;
        FOR module = tab.modules("pane", panename);
            SET src = module.definition.DesktopSrc;
            TRY;
                PROCESS $src;
            CATCH DEFAULT;
                "Bah, template $src broke on me!";
            END;
        END;
    END; %]

This worked somewhat better, and took request times from 5 seconds down
to acceptable sub-second levels again. I could take the C<view_desktop>
method out again; fewer lines of code to maintain is always good. Now
all that remained to do for the view side of the portal was to convert
our ASP templates over to something sensible.

=head2 ASP to Template Toolkit

They're all much of a muchness, these templating languages. Some of
them, though, are just a wee bit more verbose than others. For instance,
the banner template which appears in the header consists of 104 lines
of ASP code; most of those are to create the navigation bar of tabs
that we can view. Now I admit that we're slightly cheating at the moment
since we don't have the concept of a logged-in user and so we don't
distinguish between the tabs that anyone can see and those than only an
admin can see, but we'll come back to it later. Still, 104 lines, eh?

The actual tab list is presented here: (reformated slightly for sanity)

    <tr>
        <td>
            <asp:datalist id="tabs" cssclass="OtherTabsBg" 
 repeatdirection="horizontal" ItemStyle-Height="25" 
 SelectedItemStyle-CssClass="TabBg" ItemStyle-BorderWidth="1" 
 EnableViewState="false" runat="server">
                <ItemTemplate>
                    &nbsp;<a href='<%= Request.ApplicationPath %>/
 DesktopDefault.aspx?tabindex=<%# Container.ItemIndex %>&tabid=
 <%# ((TabStripDetails) Container.DataItem).TabId %>' class="OtherTabs">
 <%# ((TabStripDetails) Container.DataItem).TabName %></a>&nbsp;
                </ItemTemplate>
                <SelectedItemTemplate>
                    &nbsp;<span class="SelectedTab">
 <%# ((TabStripDetails) Container.DataItem).TabName %></span>&nbsp;
                </SelectedItemTemplate>
            </asp:datalist>
        </td>
    </tr>

But it has to be built up in some 22 lines of C# code which creates and
populates an array and then binds it to a template parameter. See those
C<E<lt>%#> and C<E<lt>%=> tags? They're the equivalent of our Template
Toolkit C<[% %]> tags. C<Request.ApplicationPath>? That's our C<base>
template argument. 

In our version we ask the portal what tabs it has, and display the
list directly, displaying the currently selected tab differently:

    <table id="Banner_tabs" class="OtherTabsBg" cellspacing="0" border="0">
        <tr>
    [% FOR a_tab = portal.tabs %]
        [% IF a_tab.id == tab.id %]
            <td class="TabBg" height="25">
                &nbsp;<span class="SelectedTab">[%tab.name%]</span>&nbsp;
        [% ELSE %]
            <td height="25">
                &nbsp;<a href='[%base%]DesktopDefault.aspx?tabid=[%a_tab.id%]' 
                class="OtherTabs">[%a_tab.name%]</a>&nbsp;
        [% END %]
            </td>
    [% END %]
        </tr>
    </table>

This is the way the world should be. But wait, where have we pulled this
C<portal> variable from? We need to tell the C<Portal> class to put the
default portal into the template arguments:

    sub additional_data {
        shift->{template_args}{portal} = Portal::Portal->retrieve(2);
    }

Translating all the other ASP.NET components is a similar exercise in drudgery;
on the whole, there was precisely nothing interesting about them at all - we
merely converted a particularly verbose templating language (and if I never see
C<asp:BoundColumn> again, it'll be no loss) into a rather more sophisticated
one.

The simplest component, F<HtmlModule.ascx>, asks a module for its associated
C<htmltexts>, and then displays the C<DesktopHtml> for each of them in a table.
This was 40 lines of ASP.NET, including more odious C# to make the SQL calls
and retrieve the C<htmltexts>. But we can do all that retrieval by magic, so
our F<HtmlModule.ascx> looks like this:

    [% PROCESS module_title %]
    <portal:title EditText="Edit" EditUrl="~/DesktopModules/EditHtml.aspx" />
    <table id="t1" cellspacing="0" cellpadding="0">
        <tr valign="top">
            <td id="HtmlHolder">
            [% FOR html = module.htmltexts; html.DesktopHtml; END %]
            </td>
        </tr>
    </table>

Now I admit that we've cheated here and kept that C<portal:title> tag
until we know what to do with it - it's obvious that we should turn
it into a link to edit the HTML of this module if we're allowed to.

The next simplest one actually did provide a slight challenge;
F<ImageModule.ascx> took the height, width and image source properties
of an image from the module's C<settings> table, and displayed an C<IMG>
tag with the appropriate values. This is only slightly difficult because
we have to arrange the array of C<module.settings> into a hash of
C<key_name> => C<setting> pairs. Frankly, I can't be bothered to do this
in the template, so we'll add it into the C<template_args> again. This
time C<addition_data> looks like:

    sub additional_data {
        my $r = shift;
        shift->{template_args}{portal} = Portal::Portal->retrieve(2);
        if ($r->{objects}->[0]->isa("Portal::Module")) {
            $r->{template_args}{module_settings} =
                { map { $_->key_name, $_->setting } 
                  $r->{objects}->[0]->settings };
        }
    }

And the F<ImageModule.ascx> drops from the 30-odd lines of ASP into:

    [% PROCESS module_title; %]
    <img id="Image1" border="0" src="[% module_settings.src %]" 
      width="[% module_settings.width %]" 
      height="[% module_settings.height %]" />
    <br>

Our portal is taking shape; after a few more templates have been translated,
we now have a complete replica of the front page of the portal and all its
tabs. It's fast, it's been developed rapidly, and it's less than 50 lines
of Perl code so far. But it's not finished yet.

=head2 Adding users