NAME

Catalyst::View::Template::BasePerRequest - Catalyst base view for per request, strongly typed templates

SYNOPSIS

package Example::View::Hello;

use Moose;

extends 'Catalyst::View::BasePerRequest';

has name => (is=>'ro', required=>1);
has age => (is=>'ro', required=>1);

sub render {
  my ($self, $c) = @_;
  return "<div>Hello @{[ $self->name] }",
    "I see you are @{[ $self->age]} years old!</div>";
}

__PACKAGE__->config(
  content_type=>'text/html',
  status_codes=>[200]
);

__PACKAGE__->meta->make_immutable();

One way to use it in a controller:

package Example::Controller::Root;

use Moose;
use MooseX::MethodAttributes;

extends 'Catalyst::Controller';

sub root :Chained(/) PathPart('') CaptureArgs(0) { } 

  sub hello :Chained(root) Args(0) {
    my ($self, $c) = @_;
    return $c->view(Hello =>
      name => 'John',
      age => 53
    )->http_ok;
  }

__PACKAGE__->config(namespace=>'');
__PACKAGE__->meta->make_immutable;

DESCRIPTION

NOTE: This is early access code. Although it's based on several other internal projects which I have iterated over this concept for a number of years I still reserve the right to make breaking changes as needed.

NOTE: You probably won't actually use this directly, it's intended to be a base framework for building / prototyping strongly typed / per request views in Catalyst. This documentation serves as an overview of the concept. In particular please note that this code does not address any issues around HTML / Javascript injection attacks or provides any auto escaping. You'll need to bake those features into whatever you build on top of this. Because of this the following documentation is light and is mostly intended to help anyone who is planning to build something on top of this framework rather than use it directly.

NOTE: This distribution's /example directory gives you a toy prototype using HTML::Tags as the basis to a view as well as some raw examples using this code directly (again, not recommended for anything other than learning).

In a classic Catalyst application with server side templates, the canonical approach is to use a 'view' as a sort of handler for an underlying template system (such as Template::Toolkit or Xslate) and to send data to this template by populating the stash. These views are very lean, and in general don't provide much in the way of view logic processing; they generally are just a thin proxy for the underlying templating system.

This approach has the upside of being very simple to understand and in general works ok with a simple websites. There are however downsides as your site becomes more complex. First of all the stash as a means to pass data from the Controller to the template can be fragile. For example just making a simple typo in the stash key can break your templates in ways that might not be easy to figure out. Also your template can't enforce its requirements very easily (and it's not easy for someone working in the controller to know exactly what things need to go into the stash in order for the template to function as desired.) The view itself has no way of providing view / display oriented logic; generally that logic ends up creeping back up into the controller in ways that break the notion of MVC's separation of concerns.

Lastly the controller doesn't have a defined API with the view. All it can ask the view is 'go ahead and process yourself using the current context' and all it gets back from the view is a string response. If the controller wishes to introspect this response or modify it in some way prior to it being sent back to the client, you have few options apart from using regular expression matching to try and extract the required information or to modify the response string.

Basically the classic approach works acceptable well for a simple website but starts to break down as your site becomes more complicated.

An alternative approach, which is explored in this distribution, is to have a defined view for each desired response and for it to define an explicit API that the controller uses to provide the required and optional data to the view. This defined view can further define its own methods used to generate suitable information for display. Such an approach is more initial work as well as learning for the website developers, but in the long term it can provide an easier path to sustainable development and maintainence with hopefully fewer bugs and overall site issues.

EXAMPLE: Basic

The most minimal thing your view must provide in a render method. This method gets the view object and the context (it can also receive additional arguments if this view is being called from other views as a wrapper or parent view; more on that later).

The render method should return a string or array of strings suitable for the body of the response> NOTE if you return an array of strings we flatten the array into a single string since the body method of Catalyst::Response can't take an array.

Here's a minimal example:

package Example::View::Hello;

use Moose;

extends 'Catalyst::View::BasePerRequest';

sub render {
  my ($self, $c) = @_;
  return "<p>Hello</p>";
}

__PACKAGE__->config(content_type=>'text/html');

And here's an example view with attributes:

package Example::View::HelloPerson;

use Moose;

extends 'Catalyst::View::BasePerRequest';

has name => (is=>'ro', required=>1);

sub render {
  my ($self, $c) = @_;
  return qq[
    <div>
      Hello  @{[ $self->name ]}
    </div>];
}

__PACKAGE__->meta->make_immutable();

One way to invoke this view from the controller using the traditional forward method:

package Example::Controller::Root;

use Moose;
use MooseX::MethodAttributes;

extends 'Catalyst::Controller';

sub root :Chained(/) PathPart('') CaptureArgs(0) { }

  sub hello :Chained(root) Args(0) {
    my ($self, $c) = @_;
    my $view = $c->view(HelloPerson => (name => 'John'));
    return $c->forward($view);
  }

__PACKAGE__->config(namespace=>'');
__PACKAGE__->meta->make_immutable;

Alternatively using "RESPONSE HELPERS":

package Example::Controller::Root;

use Moose;
use MooseX::MethodAttributes;

extends 'Catalyst::Controller';

sub root :Chained(/) PathPart('') CaptureArgs(0) { }

  sub hello :Chained(root) Args(0) {
    my ($self, $c) = @_;
    return $c->view(HelloPerson => (name => 'John'))->http_ok;
  }

__PACKAGE__->config(namespace=>'');
__PACKAGE__->meta->make_immutable;

ATTRIBUTES

The following Moose attributes are considered part of this classes public API

app

The string namespace of your Catalyst application.

ctx

The current Catalyst context

root

The root view object (that is the top view that was called first, usually from the controller).

parent

has_parent

If the view was called from another view, that first view is set as the parent.

injected_views

has_injected_views

An arrayref of the method names associated with any injected views.

METHODS

The following methods are considered part of this classes public API

process

Renders a view and sets up the response object. Generally this is called from a controller via the forward method and not directly:

$c->forward($view);

respond

Accepts an HTTP status code and an arrayref of key / values used to set HTTP headers for a response. Example:

$view->respond(201, [ location=>$url ]);

Returns the view object to make it easier to do method chaining

detach

Just a shortcut to ->detach via the context

CONTENT BLOCK HELPERS

Content block helpers are an optional feature to make it easy to create and populate content areas between different views. Although you can also do this with object attributes you may wish to separate template / text from data. Example:

package Example::View::Layout;

use Moose;

extends 'Catalyst::View::BasePerRequest';

has title => (is=>'ro', required=>1, default=>'Missing Title');

sub render {
  my ($self, $c, $inner) = @_;
  return "
    <html>
      <head>
        <title>@{[ $self->title ]}</title>
        @{[ $self->content('css') ]}
      </head>
      <body>$inner</body>
    </html>";
}

__PACKAGE__->config(content_type=>'text/html');
__PACKAGE__->meta->make_immutable();

package Example::View::Hello;

use Moose;

extends 'Catalyst::View::BasePerRequest';

has name => (is=>'ro', required=>1);

sub render {
  my ($self, $c) = @_;
  return $c->view(Layout => title=>'Hello', sub {
    my $layout = shift;
    $self->content_for('css', "<style>...</style>");
    return "<div>Hello @{[ $self->name ]}!</div>";
  });
}

__PACKAGE__->config(content_type=>'text/html', status_codes=>[200]);
__PACKAGE__->meta->make_immutable();

content_for

$self->content_for($name, $string);
$self->content_for($name, $\&callback);

Sets a named content block or throws an exception if the content block already exists.

$self->content_for('hello', sub {
  my ($name) = @_;
  return "Hello $name!";
});

content

Examples:

$self->content($name, ?@args, ?\&default);

Gets a content block string by '$name'. If the block has not been defined returns either a zero length string or whatever you set the default code block to be. Examples:

$self->content('hello', 'John', sub { return "$name!" });

content_append

Appends to a named content block or throws an exception if the content block doesn't exist.

content_replace

Replaces a named content block or throws an exception if the content block doesn't exist.

content_around

Wraps an existing content with new content. Throws an exception if the named content block doesn't exist.

$self->content_around('footer', sub {
  my $footer = $_[0]->();
  return "wrapped $footer end wrap";
});

VIEW INJECTION

Usually when building a website of more than toy complexity you will find that you will decompose your site into sub views and view wrappers. Although you can call the view method on the context, I think its more in the spirit of the idea of a strong or structured view to have a view declare upfront what views its calling as sub views. That lets you have more central control over view initalization and decouples how you are calling your views from the actual underlying views. It can also tidy up some of the code and lastly makes it easy to immediately know what views are needed for the current one. This can help with later refactoring (I've worked on projects where sub views got detached from actual use but nobody ever cleaned them up.)

To inject a view into the current one, you need to declare it in configuration:

__PACKAGE__->config(
  content_type=>'text/html', 
  status_codes=>[200,404,400],
  views=>+{
    layout1 => [ Layout => sub { my ($self, $c) = @_; return title=>'Hey!' } ],
    layout2 => [ Layout => (title=>'Yeah!') ],
    layout3 => 'Layout',
  },
);

Basically this is a hashref under the views key, where each key in the hashref is the name of the method you are injecting into the current view which is responsible for creating the sub view and the value is one of three options:

A scalar value

__PACKAGE__->config(
  content_type=>'text/html', 
  status_codes=>[200,404,400],
  views=>+{
    layout => 'Layout',
  },
);

This is the simplest option, it just injects a method that will call the named view and pass any arguments from the method but does not add any global arguments.

An arrayref

__PACKAGE__->config(
  content_type=>'text/html', 
  status_codes=>[200,404,400],
  views=>+{
    layout => [ Layout => (title=>'Yeah!') ],
  },
);

This option allows you to set some argument defaults to the view called. The first item in the arrayref must be the real name of the view, followed by arguments which are merged with any provided to the method.

A coderef

__PACKAGE__->config(
  content_type=>'text/html', 
  status_codes=>[200,404,400],
  views=>+{
    layout => [ Layout => sub { my ($self, $c) = @_; return title=>'Hey!' } ],
  },
);

The most complex option, you should probably reserve for very special needs. Basically this coderef will be called with the current view instance and Catalyst context; it should return arguments which with then be merged and treated as in the arrayref option.

Now you can call for the sub view via a simple method call on the view, rather than via the context:

package Example::View::Hello;

use Moose;

extends 'Catalyst::View::BasePerRequest';

has name => (is=>'ro', required=>1);
has age => (is=>'ro', required=>1);


sub render {
  my ($self, $c) = @_;

  return $self->layout(title=>'Hello!', sub {
    my $layout = shift;
    return "Hello @{[$self->name]}; you are @{[$self->age]} years old!";  
  });
}


__PACKAGE__->config(
  content_type=>'text/html', 
  status_codes=>[200,404,400],
  views=>+{
    layout => 'Layout',
  },
);

__PACKAGE__->meta->make_immutable;

RESPONSE HELPERS

When you create a view instance the actual response is not send to the client until the "respond" method is called (either directly, via "process" or thru the generated response helpers).

Response helpers are just methods that call "respond" with the correct status code and using a more easy to remember name (and possibly a more self documenting one).

For example:

$c->view('Login')->http_ok;

calls the "respond" method with the expected http status code. You can also pass arguments to the response helper which are send to "respond" and used to add HTTP headers to the response.

$c->view("NewUser")
  ->http_created(location=>$url);

Please note that calling a response helper only sets up the response object, it doesn't stop any future actions in you controller. If you really want to stop action processing you'll need to call "detach":

return $c->view("Error")
  ->http_bad_request
  ->detach;

If you don't want to generate the response yet (perhaps you'll leave that to a global 'end' action) you can use the 'set_http_$STATUS' helpers instead which wil just set the response status.

return $c->view("Error")
  ->set_http_bad_request
  ->detach;

Response helpers are just lowercased names you'll find for the codes listed in HTTP::Status. Some of the most common ones I find in my code:

http_ok
http_created
http_bad_request
http_unauthorized
http_not_found
http_internal_server_error

By default we create response helpers for all the status codes in HTTP::Status. However if you set the status_codes configuration key (see "status_codes") you can limit the generated helpers to specific codes. This can be useful since most views are only meaningful with a limited set of response codes.

APPLICATION CONTEXT

Generally views using this will need to be called in request context (that is with a Catalyst context, or '$c'). However if you call the view in application context you will get the underlying factory object. Useful if you need access to any complex constructs built at startup.

If none of this makes sense to you, you don't need to worry about it. It's advanced edge case stuff. Added because I found a use case around view inheritance.

RUNTIME HOOKS

This class defines the following method hooks you may optionally defined in your view subclass in order to control or otherwise influence how the view works.

$class->modify_init_args($app, $args)

Runs when COMPONENT is called during setup_components. This gets a reference to the merged arguments from all configuration. You should return this reference after modification.

This is for modifying or adding arguments that are application scoped rather than context scoped.

prepare_build_args

This method will be called (if defined) by the factory class during build time. It can be used to inject args and modify args. It gets the context and @args as arguments and should return all the arguments you want to pass to new. Example:

sub prepare_build_args {
  my ($class, $c, @args) = @_;
  # Mess with @args
  return @args;
}

build

Receives the initialization hash and should return a new instance of the the view. By default this just calls new on the class with the hash of args but if you need to call some other method or have some complex initialization work that can't be handled with "prepare_build_args" you can override.

CONFIGURATION

This Catalyst Component supports the following configuation.

content_type

The HTTP content type of the response. For example 'text/html'. Required.

status_codes

An ArrayRef of HTTP status codes used to provide response helpers. This is optional but it allows you to specify the permitted HTTP response codes that a template can generate. for example a NotFound view probably makes no sense to return anything other than a 404 Not Found code.

lifecycle

By default your view lifecycle is 'per request' which means we only build it one during the entire request cycle. This is handled by the lifecycle module Catalyst::View::BasePerRequest::Lifecycle::Request. However sometimes you would like your view to be build newly each you you request it. For example you might have a view called from inside a loop, passing it different arguments each time. In that case you want the 'Factory' lifecycle, which is handled by Catalyst::View::BasePerRequest::Lifecycle::Factory. In order to do that set this configuration value to 'Factory'. For example

__PACKAGE__->config(
  content_type => 'text/html', 
  status_codes => [200,201,400],
  lifecycle => 'Factory',
);

You can create your own lifecycle classes, but that's very advanced so for now if you want to do that you should review the source of the existing ones. D-dor example you might create a view with a 'session' lifecycle, which returns the same view as long as the user is logged in.

ALSO SEE

Catalyst

AUTHORS & COPYRIGHT

John Napiorkowski email:jjnapiork@cpan.org

LICENSE

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

To install Catalyst::View::BasePerRequest, copy and paste the appropriate command in to your terminal.

cpanm

cpanm Catalyst::View::BasePerRequest

CPAN shell

perl -MCPAN -e shell
install Catalyst::View::BasePerRequest

For more information on module installation, please visit the detailed CPAN module installation guide.

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