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Think about Loose Coupling

Re^3: Implementing Model-View-Controller

by jZed (Prior)
on Jan 05, 2006 at 18:19 UTC ( #521306=note: print w/replies, xml ) Need Help??

in reply to Re^2: Implementing Model-View-Controller
in thread Implementing Model-View-Controller

package main; # Controller; for my $foodtype(sort keys %{$Model::data}) { my $food = Model::get_food($foodtype); View::show_food($foodtype,$food); }

You're right that my example that used qw(fruits vegies) gave the Controller knowledge of the Model. But so does yours. Yours breaks the MVC separation because the Controller now needs to know that the Model stores its data in a hash. If we add sub get_keys { sort keys %$data } to the Model, the Controller can then do this: for my $foodtype( Model::get_keys ) ... and thus be freed from knowing anything about how the Model stores things. If the Model changes to using a database, you could still have a Model::get_keys() method that would do a DISTINCT query and the Controller wouldn't need to change at all.

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Re^4: Implementing Model-View-Controller
by dimar (Curate) on Jan 05, 2006 at 19:33 UTC

    No sweat. I just followed up to address the issue to the OP (specifically, the OP's concern that inter-component changes in MVC must somehow be a hassle).

    I must admit, however, I was a little surprised that you did not define Model to look something more like:

    my $data = [ {type=>'fruit',food='apple'}, {type=>'veggies',food='carrot'}, {type=>'meat',food='bacon'}, ];
    my $data = [ [qw(fruit apple)], [qw(veggies carrot)], ];

    This is the approach I tend to use most often (with obvious anticipation that "M" will be eventually migrated to a database). I almost always use AoH in fact.

    Yours breaks the MVC separation because the Controller now needs to know that the Model stores its data in a hash ...

    Perhaps, although I don't think it necessarily 'breaks' the pattern to introduce simplifying assumptions about M (especially in tutorial-type code examples like here). Unless your MVC framework always uses reflection, or a sufficiently expressive and universally disambiguating syntax, your V and your C are going to have to know at least *something* about your M.

    Anyway, I just figured you were trying to save some typing ... (which is why I didn't even bother to give a code example at all in my first response ;-).


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