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1 | =head1 NAME |
2 | |
3 | Catalyst::Manual::ExtendingCatalyst - Extending The Framework |
4 | |
5 | =head1 DESCRIPTION |
6 | |
7 | This document will provide you with access points, techniques and best |
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8 | practices to extend the L<Catalyst> framework, or to find more elegant |
9 | ways to abstract and use your own code. |
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10 | |
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11 | The design of Catalyst is such that the framework itself should not |
12 | get in your way. There are many entry points to alter or extend |
13 | Catalyst's behaviour, and this can be confusing. This document is |
14 | written to help you understand the possibilities, current practices |
15 | and their consequences. |
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16 | |
17 | Please read the L<BEST PRACTICES> section before deciding on a design, |
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18 | especially if you plan to release your code to CPAN. The Catalyst |
19 | developer and user communities, which B<you are part of>, will benefit |
20 | most if we all work together and coordinate. |
21 | |
22 | If you are unsure on an implementation or have an idea you would like |
23 | to have RFC'ed, it surely is a good idea to send your questions and |
24 | suggestions to the Catalyst mailing list (See L<Catalyst/SUPPORT>) |
25 | and/or come to the C<#catalyst> channel on the C<irc.perl.org> |
26 | network. You might also want to refer to those places for research to |
27 | see if a module doing what you're trying to implement already |
28 | exists. This might give you a solution to your problem or a basis for |
29 | starting. |
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30 | |
31 | =head1 BEST PRACTICES |
32 | |
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33 | During Catalyst's early days, it was common to write plugins to |
34 | provide functionality application wide. Since then, Catalyst has |
35 | become a lot more flexible and powerful. It soon became a best |
36 | practice to use some other form of abstraction or interface, to keep |
37 | the scope of its influence as close as possible to where it belongs. |
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38 | |
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39 | For those in a hurry, here's a quick checklist of some fundamental |
40 | points. If you are going to read the whole thing anyway, you can jump |
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41 | forward to L</Namespaces>. |
42 | |
43 | =head2 Quick Checklist |
44 | |
45 | =over |
46 | |
47 | =item Use the C<CatalystX::*> namespace if you can! |
48 | |
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49 | If your extension isn't a Model, View, Controller, Plugin, Engine, |
50 | or Log, it's best to leave it out of the C<Catalyst::> namespace. |
51 | Use <CatalystX::> instead. |
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52 | |
53 | =item Don't make it a plugin unless you have to! |
54 | |
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55 | A plugin should be careful since it's overriding Catalyst internals. |
56 | If your plugin doesn't really need to muck with the internals, make it a |
57 | base Controller or Model. |
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58 | |
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59 | Also, if you think you really need a plugin, please instead consider |
60 | using a L<Moose::Role>. |
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61 | |
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62 | =item There's a community. Use it! |
63 | |
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64 | There are many experienced developers in the Catalyst community, |
65 | there's always the IRC channel and the mailing list to discuss things. |
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66 | |
67 | =item Add tests and documentation! |
68 | |
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69 | This gives a stable basis for contribution, and even more importantly, |
70 | builds trust. The easiest way is a test application. See |
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71 | L<Catalyst::Manual::Tutorial::Testing> for more information. |
72 | |
73 | =back |
74 | |
75 | =head2 Namespaces |
76 | |
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77 | While some core extensions (engines, plugins, etc.) have to be placed |
78 | in the C<Catalyst::*> namespace, the Catalyst core would like to ask |
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79 | developers to use the C<CatalystX::*> namespace if possible. |
80 | |
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81 | Please B<do not> invent components which are outside the well |
82 | known C<Model>, C<View>, C<Controller> or C<Plugin> namespaces! |
83 | |
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84 | When you try to put a base class for a C<Model>, C<View> or |
85 | C<Controller> directly under your C<MyApp> directory as, for example, |
86 | C<MyApp::Controller::Foo>, you will have the problem that Catalyst |
87 | will try to load that base class as a component of your |
88 | application. The solution is simple: Use another namespace. Common |
89 | ones are C<MyApp::Base::Controller::*> or C<MyApp::ControllerBase::*> |
90 | as examples. |
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91 | |
92 | =head2 Can it be a simple module? |
93 | |
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94 | Sometimes you want to use functionality in your application that |
95 | doesn't require the framework at all. Remember that Catalyst is just |
96 | Perl and you always can just C<use> a module. If you have application |
97 | specific code that doesn't need the framework, there is no problem in |
98 | putting it in your C<MyApp::*> namespace. Just don't put it in |
99 | C<Model>, C<Controller> or C<View>, because that would make Catalyst |
100 | try to load them as components. |
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101 | |
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102 | Writing a generic component that only works with Catalyst is wasteful |
103 | of your time. Try writing a plain perl module, and then a small bit |
104 | of glue that integrates it with Catalyst. See |
105 | L<Catalyst::Model::DBIC::Schema|Catalyst::Model::DBIC::Schema> for a |
106 | module that takes the approach. The advantage here is that your |
107 | "Catalyst" DBIC schema works perfectly outside of Catalyst, making |
108 | testing (and command-line scripts) a breeze. The actual Catalyst |
109 | Model is just a few lines of glue that makes working with the schema |
110 | convenient. |
111 | |
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112 | If you want the thinnest interface possible, take a look at |
113 | L<Catalyst::Model::Adaptor|Catalyst::Model::Adaptor>. |
114 | |
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115 | =head2 Using Moose roles to apply method modifiers |
116 | |
117 | Rather than having a complex set of base classes which you have to mixin |
118 | via multiple inheritence, if your functionality is well structured, then |
119 | it's possible to use the composability of L<Moose> roles, and method modifiers |
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120 | to hook onto to provide functionality. |
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121 | |
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122 | These can be applied to your models/views/controllers, and your application |
123 | class. Please see the sections below for special notes and caveats, and |
124 | the L<Moose::Manual::Roles> for more information about roles in general. |
125 | |
126 | =head3 In your application class |
127 | |
128 | It should be noted that when applying roles to your application class, that |
129 | you should B<not> wrap methods provided by L<Catalyst> until B<after> you have |
130 | run C<< __PACKAGE__->setup >>, as your class does not inherit from any of your |
131 | plugins until the setup method is run. |
132 | |
133 | With Catalyst 5.80004, it is possible to include Roles in the plugin list, and |
134 | these roles will be applied to your application class immediately after |
135 | 'traditional' plugins have been composed into your application class' |
136 | inheritance hierarchy. |
137 | |
138 | =head3 In controllers |
139 | |
140 | Method modifiers on controller actions will work as expected (either in your |
141 | controllers, or when composed from roles) in Catalyst 5.80003 and above. |
142 | |
143 | It is possible to have action methods with attributes inside Moose roles, using |
144 | the trait introduced in L<MooseX::MethodAttributes> version 0.12, example: |
145 | |
146 | package MyApp::ControllerRole; |
147 | use Moose::Role -traits => 'MethodAttributes'; |
148 | |
149 | sub foo : Local { |
150 | my ($self, $c) = @_; |
151 | ... |
152 | } |
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153 | |
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154 | =head2 Inheritance and overriding methods |
155 | |
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156 | When overriding a method, keep in mind that some day additionall |
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157 | arguments may be provided to the method, if the last parameter is not |
158 | a flat list. It is thus better to override a method by shifting the |
159 | invocant off of C<@_> and assign the rest of the used arguments, so |
160 | you can pass your complete arguments to the original method via C<@_>: |
161 | |
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162 | use MRO::Compat; ... |
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163 | |
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164 | sub foo { |
165 | my $self = shift; |
166 | my ($bar, $baz) = @_; # ... return |
167 | $self->next::method(@_); |
168 | } |
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169 | |
170 | If you would do the common |
171 | |
172 | my ($self, $foo, $bar) = @_; |
173 | |
174 | you'd have to use a much uglier construct to ensure that all arguments |
175 | will be passed along and the method is future proof: |
176 | |
177 | $self->next::method(@_[ 1 .. $#_ ]); |
178 | |
179 | =head2 Tests and documentation |
180 | |
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181 | When you release your module to the CPAN, proper documentation and at |
182 | least a basic test suite (which means more than pod or even just |
183 | C<use_ok>, sorry) gives people a good base to contribute to the |
184 | module. It also shows that you care for your users. If you would like |
185 | your module to become a recommended addition, these things will prove |
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186 | invaluable. |
187 | |
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188 | If you're just getting started, try using |
189 | L<CatalystX::Starter|CatalystX::Starter> to generate some example |
190 | tests for your module. |
191 | |
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192 | =head2 Maintenance |
193 | |
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194 | In planning to release a module to the community (Catalyst or CPAN and |
195 | Perl), you should consider if you have the resources to keep it up to |
196 | date, including fixing bugs and accepting contributions. |
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197 | |
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198 | If you're not sure about this, you can always ask in the proper |
199 | Catalyst or Perl channels if someone else might be interested in the |
200 | project, and would jump in as co-maintainer. |
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201 | |
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202 | A public repository can further ease interaction with the |
203 | community. Even read only access enables people to provide you with |
204 | patches to your current development version. subversion, SVN and SVK, |
205 | are broadly preferred in the Catalyst community. |
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206 | |
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207 | If you're developing a Catalyst extension, please consider asking the |
208 | core team for space in Catalyst's own subversion repository. You can |
209 | get in touch about this via IRC or the Catalyst developers mailing |
210 | list. |
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211 | |
212 | =head2 The context object |
213 | |
214 | Sometimes you want to get a hold of the context object in a component |
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215 | that was created on startup time, where no context existed yet. Often |
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216 | this is about the model reading something out of the stash or other |
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217 | context information (current language, for example). |
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218 | |
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219 | If you use the context object in your component you have tied it to an |
220 | existing request. This means that you might get into problems when |
221 | you try to use the component (e.g. the model - the most common case) |
222 | outside of Catalyst, for example in cronjobs. |
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223 | |
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224 | A stable solution to this problem is to design the Catalyst model |
225 | separately from the underlying model logic. Let's take |
226 | L<Catalyst::Model::DBIC::Schema> as an example. You can create a |
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227 | schema outside of Catalyst that knows nothing about the web. This kind |
228 | of design ensures encapsulation and makes development and maintenance |
229 | a whole lot easier. The you use the aforementioned model to tie your |
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230 | schema to your application. This gives you a C<MyApp::DBIC> (the name |
231 | is of course just an example) model as well as |
232 | C<MyApp::DBIC::TableName> models to access your result sources |
233 | directly. |
234 | |
235 | By creating such a thin layer between the actual model and the |
236 | Catalyst application, the schema itself is not at all tied to any |
237 | application and the layer in-between can access the model's API using |
238 | information from the context object. |
239 | |
240 | A Catalyst component accesses the context object at request time with |
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241 | L<Catalyst::Component/"ACCEPT_CONTEXT($c, @args)">. |
242 | |
243 | =head1 CONFIGURATION |
244 | |
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245 | The application has to interact with the extension with some |
246 | configuration. There is of course again more than one way to do it. |
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247 | |
248 | =head2 Attributes |
249 | |
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250 | You can specify any valid Perl attribute on Catalyst actions you like. |
251 | (See L<attributes/"Syntax of Attribute Lists"> for a description of |
252 | what is valid.) These will be available on the C<Catalyst::Action> |
253 | instance via its C<attributes> accessor. To give an example, this |
254 | action: |
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255 | |
256 | sub foo : Local Bar('Baz') { |
257 | my ($self, $c) = @_; |
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258 | my $attributes = |
259 | $self->action_for('foo')->attributes; |
260 | $c->res->body($attributes->{Bar}[0] ); |
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261 | } |
262 | |
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263 | will set the response body to C<Baz>. The values always come in an |
264 | array reference. As you can see, you can use attributes to configure |
265 | your actions. You can specify or alter these attributes via |
266 | L</"Component Configuration">, or even react on them as soon as |
267 | Catalyst encounters them by providing your own L<component base |
268 | class|/"Component Base Classes">. |
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269 | |
270 | =head2 Creating custom accessors |
271 | |
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272 | L<Catalyst::Component> uses L<Class::Accessor::Fast> for accessor |
273 | creation. Please refer to the modules documentation for usage |
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274 | information. |
275 | |
276 | =head2 Component configuration |
277 | |
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278 | At creation time, the class configuration of your component (the one |
279 | available via C<$self-E<gt>config>) will be merged with possible |
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280 | configuration settings from the applications configuration (either |
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281 | directly or via config file). This is then stored in the controller |
282 | object's hash reference. So, if you read possible configurations like: |
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283 | |
284 | my $model_name = $controller->{model_name}; |
285 | |
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286 | you will get the right value. The C<config> accessor always only |
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287 | contains the original class configuration and must not be used for |
288 | component configuration. |
289 | |
290 | You are advised to create accessors on your component class for your |
291 | configuration values. This is good practice and makes it easier to |
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292 | capture configuration key typos. You can do this with the |
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293 | C<mk_ro_accessors> method provided to L<Catalyst::Component> via |
294 | L<Class::Accessor::Fast>: |
295 | |
296 | use base 'Catalyst::Controller'; |
297 | __PACKAGE__->mk_ro_accessors('model_name'); |
298 | ... |
299 | my $model_name = $controller->model_name; |
300 | |
301 | =head1 IMPLEMENTATION |
302 | |
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303 | This part contains the technical details of various implementation |
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304 | methods. Please read the L</"BEST PRACTICES"> before you start your |
305 | implementation, if you haven't already. |
306 | |
307 | =head2 Action classes |
308 | |
309 | Usually, your action objects are of the class L<Catalyst::Action>. |
310 | You can override this with the C<ActionClass> attribute to influence |
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311 | execution and/or dispatching of the action. A widely used example of |
312 | this is L<Catalyst::Action::RenderView>, which is used in every newly |
313 | created Catalyst application in your root controller: |
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314 | |
315 | sub end : ActionClass('RenderView') { } |
316 | |
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317 | Usually, you want to override the C<execute> and/or the C<match> |
318 | method. The execute method of the action will naturally call the |
319 | methods code. You can surround this by overriding the method in a |
320 | subclass: |
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321 | |
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322 | package Catalyst::Action::MyFoo; |
323 | use strict; |
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324 | |
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325 | use MRO::Compat; |
326 | use base 'Catalyst::Action'; |
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327 | |
328 | sub execute { |
329 | my $self = shift; |
330 | my ($controller, $c, @args) = @_; |
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331 | # put your 'before' code here |
332 | my $r = $self->next::method(@_); |
333 | # put your 'after' code here |
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334 | return $r; |
335 | } |
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336 | 1; |
337 | |
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338 | We are using L<MRO::Compat> to ensure that you have the next::method |
339 | call, from L<Class::C3> (in older perls), or natively (if you are using |
340 | perl 5.10) to re-dispatch to the original C<execute> method in the |
341 | L<Catalyst::Action> class. |
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342 | |
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343 | The Catalyst dispatcher handles an incoming request and, depending |
344 | upon the dispatch type, will call the appropriate target or chain. |
345 | From time to time it asks the actions themselves, or through the |
346 | controller, if they would match the current request. That's what the |
347 | C<match> method does. So by overriding this, you can change on what |
348 | the action will match and add new matching criteria. |
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349 | |
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350 | For example, the action class below will make the action only match on |
351 | Mondays: |
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352 | |
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353 | package Catalyst::Action::OnlyMondays; |
354 | use strict; |
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355 | |
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356 | use MRO::Compat; |
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357 | use base 'Catalyst::Action'; |
358 | |
359 | sub match { |
360 | my $self = shift; |
361 | return 0 if ( localtime(time) )[6] == 1; |
362 | return $self->next::method(@_); |
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363 | } |
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364 | 1; |
365 | |
366 | And this is how we'd use it: |
367 | |
368 | sub foo: Local ActionClass('OnlyMondays') { |
369 | my ($self, $c) = @_; |
370 | $c->res->body('I feel motivated!'); |
371 | } |
372 | |
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373 | If you are using action classes often or have some specific base |
374 | classes that you want to specify more conveniently, you can implement |
375 | a component base class providing an attribute handler. |
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376 | |
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377 | For further information on action classes, please refer to |
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378 | L<Catalyst::Action> and L<Catalyst::Manual::Actions>. |
379 | |
380 | =head2 Component base classes |
381 | |
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382 | Many L<Catalyst::Plugin> that were written in Catalyst's early days |
383 | should really have been just controller base classes. With such a |
384 | class, you could provide functionality scoped to a single controller, |
385 | not polluting the global namespace in the context object. |
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386 | |
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387 | You can provide regular Perl methods in a base class as well as |
388 | actions which will be inherited to the subclass. Please refer to |
389 | L</Controllers> for an example of this. |
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390 | |
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391 | You can introduce your own attributes by specifying a handler method |
392 | in the controller base. For example, to use a C<FullClass> attribute |
393 | to specify a fully qualified action class name, you could use the |
394 | following implementation. Note, however, that this functionality is |
395 | already provided via the C<+> prefix for action classes. A simple |
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396 | |
397 | sub foo : Local ActionClass('+MyApp::Action::Bar') { ... } |
398 | |
399 | will use C<MyApp::Action::Bar> as action class. |
400 | |
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401 | package MyApp::Base::Controller::FullClass; use strict; use base |
402 | 'Catalyst::Controller'; |
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403 | |
404 | sub _parse_FullClass_attr { |
405 | my ($self, $app_class, $action_name, $value, $attrs) = @_; |
406 | return( ActionClass => $value ); |
407 | } |
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408 | 1; |
409 | |
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410 | Note that the full line of arguments is only provided for completeness |
411 | sake. We could use this attribute in a subclass like any other |
412 | Catalyst attribute: |
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413 | |
414 | package MyApp::Controller::Foo; |
415 | use strict; |
416 | use base 'MyApp::Base::Controller::FullClass'; |
417 | |
418 | sub foo : Local FullClass('MyApp::Action::Bar') { ... } |
419 | |
420 | 1; |
421 | |
422 | =head2 Controllers |
423 | |
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424 | Many things can happen in controllers, and it often improves |
425 | maintainability to abstract some of the code out into reusable base |
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426 | classes. |
427 | |
428 | You can provide usual Perl methods that will be available via your |
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429 | controller object, or you can even define Catalyst actions which will |
430 | be inherited by the subclasses. Consider this controller base class: |
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431 | |
432 | package MyApp::Base::Controller::ModelBase; |
433 | use strict; |
434 | use base 'Catalyst::Controller'; |
435 | |
436 | sub list : Chained('base') PathPart('') Args(0) { |
437 | my ($self, $c) = @_; |
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438 | my $model = $c->model( $self->{model_name} ); |
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439 | my $condition = $self->{model_search_condition} || {}; |
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440 | my $attrs = $self->{model_search_attrs} || {}; |
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441 | $c->stash(rs => $model->search($condition, $attrs); |
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442 | } |
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443 | |
444 | sub load : Chained('base') PathPart('') CaptureArgs(1) { |
445 | my ($self, $c, $id) = @_; |
446 | my $model = $c->model( $self->{model_name} ); |
447 | $c->stash(row => $model->find($id)); |
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448 | } |
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449 | 1; |
450 | |
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451 | This example implements two simple actions. The C<list> action chains |
452 | to a (currently non-existent) C<base> action and puts a result-set |
453 | into the stash taking a configured C<model_name> as well as a search |
454 | condition and attributes. This action is a |
455 | L<chained|Catalyst::DispatchType::Chained> endpoint. The other action, |
456 | called C< load > is a chain midpoint that takes one argument. It takes |
457 | the value as an ID and loads the row from the configured model. Please |
458 | not that the above code is simplified for clarity. It misses error |
459 | handling, input validation, and probably other things. |
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460 | |
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461 | The class above is not very useful on its own, but we can combine it |
462 | with some custom actions by sub-classing it: |
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463 | |
464 | package MyApp::Controller::Foo; |
465 | use strict; |
466 | use base 'MyApp::Base::Controller::ModelBase'; |
467 | |
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468 | __PACKAGE__->config( model_name => 'DB::Foo', |
469 | model_search_condition=> { is_active => 1 }, |
470 | model_search_attrs => { order_by => 'name' }, |
471 | ); |
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472 | |
473 | sub base : Chained PathPart('foo') CaptureArgs(0) { } |
474 | |
475 | sub view : Chained('load') Args(0) { |
476 | my ($self, $c) = @_; |
477 | my $row = $c->stash->{row}; |
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478 | $c->res->body(join ': ', $row->name, |
479 | $row->description); } |
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480 | 1; |
481 | |
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482 | This class uses the formerly created controller as a base |
483 | class. First, we see the configurations that were used in the parent |
484 | class. Next comes the C<base> action, where everything chains off of. |
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485 | |
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486 | Note that inherited actions act like they were declared in your |
487 | controller itself. You can therefor call them just by their name in |
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488 | C<forward>s, C<detaches> and C<Chained(..)> specifications. This is an |
489 | important part of what makes this technique so useful. |
490 | |
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491 | The new C<view> action ties itself to the C<load> action specified in |
492 | the base class and outputs the loaded row's C<name> and C<description> |
493 | columns. The controller C<MyApp::Controller::Foo> now has these |
494 | publicly available paths: |
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495 | |
496 | =over |
497 | |
498 | =item /foo |
499 | |
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500 | Will call the controller's C<base>, then the base classes C<list> |
501 | action. |
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502 | |
503 | =item /foo/$id/view |
504 | |
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505 | First, the controller's C<base> will be called, then it will C<load> |
506 | the row with the corresponding C<$id>. After that, C<view> will |
507 | display some fields out of the object. |
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508 | |
509 | =back |
510 | |
511 | =head2 Models and Views |
512 | |
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513 | If the functionality you'd like to add is really a data-set that you |
514 | want to manipulate, for example internal document types, images, |
515 | files, it might be better suited as a model. |
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516 | |
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517 | The same applies for views. If your code handles representation or |
518 | deals with the applications interface and should be universally |
519 | available, it could be a perfect candidate for a view. |
38017482 |
520 | |
b7c570ac |
521 | Please implement a C<process> method in your views. This method will |
522 | be called by Catalyst if it is asked to forward to a component without |
523 | a specified action. Note that C<process> is B<not a Catalyst action> |
524 | but a simple Perl method. |
38017482 |
525 | |
526 | You are also encouraged to implement a C<render> method corresponding |
527 | with the one in L<Catalyst::View::TT>. This has proven invaluable, |
528 | because people can use your view for much more fine-grained content |
529 | generation. |
530 | |
531 | Here is some example code for a fictional view: |
532 | |
533 | package CatalystX::View::MyView; |
534 | use strict; |
535 | use base 'Catalyst::View'; |
536 | |
537 | sub process { |
538 | my ($self, $c) = @_; |
38017482 |
539 | my $template = $c->stash->{template}; |
b7c570ac |
540 | my $content = $self->render($c, $template, $c->stash); |
38017482 |
541 | $c->res->body( $content ); |
542 | } |
543 | |
544 | sub render { |
545 | my ($self, $c, $template, $args) = @_; |
b7c570ac |
546 | # prepare content here |
38017482 |
547 | return $content; |
548 | } |
38017482 |
549 | 1; |
550 | |
551 | =head2 Plugins |
552 | |
b7c570ac |
553 | The first thing to say about plugins is that if you're not sure if |
554 | your module should be a plugin, it probably shouldn't. It once was |
555 | common to add features to Catalyst by writing plugins that provide |
556 | accessors to said functionality. As Catalyst grew more popular, it |
557 | became obvious that this qualifies as bad practice. |
558 | |
559 | By designing your module as a Catalyst plugin, every method you |
560 | implement, import or inherit will be available via your applications |
561 | context object. A plugin pollutes the global namespace, and you |
562 | should be only doing that when you really need to. |
563 | |
564 | Often, developers design extensions as plugins because they need to |
565 | get hold of the context object. Either to get at the stash or |
566 | request/response objects are the widely spread reasons. It is, |
567 | however, perfectly possible to implement a regular Catalyst component |
568 | (read: model, view or controller) that receives the current context |
569 | object via L<Catalyst::Component/"ACCEPT_CONTEXT($c, @args)">. |
570 | |
571 | When is a plugin suited to your task? Your code needs to be a |
572 | plugin to act upon or alter specific parts of Catalyst's request |
78170776 |
573 | lifecycle. If your functionality needs to change some C<prepare_*> or |
b7c570ac |
574 | C<finalize_*> stages, you won't get around a plugin. |
575 | |
78170776 |
576 | Note, if you just want to hook into such a stage, and run code before, |
577 | or after it, then it is recommended that you use L<Moose>s method modifiers |
578 | to do this. |
579 | |
b7c570ac |
580 | Another valid target for a plugin architecture are things that |
581 | B<really> have to be globally available, like sessions or |
582 | authentication. |
583 | |
584 | B<Please do not> release Catalyst extensions as plugins only to |
585 | provide some functionality application wide. Design it as a controller |
586 | base class or another suiting technique with a smaller scope, so that |
587 | your code only influences those parts of the application where it is |
588 | needed, and namespace clashes and conflicts are ruled out. |
38017482 |
589 | |
590 | The implementation is pretty easy. Your plugin will be inserted in the |
591 | application's inheritance list, above Catalyst itself. You can by this |
b7c570ac |
592 | alter Catalyst's request lifecycle behaviour. Every method you |
593 | declare, every import in your package will be available as method on |
594 | the application and the context object. As an example, let's say you |
78170776 |
595 | want Catalyst to warn you every time uri_for was called without an action |
596 | object as the first parameter, for example to test that all your chained |
597 | uris are generated from actions (a recommended best practice). |
598 | You could do this with this simple |
38017482 |
599 | implementation (excuse the lame class name, it's just an example): |
600 | |
601 | package Catalyst::Plugin::UriforUndefWarning; |
602 | use strict; |
78170776 |
603 | use Scalar::Util qw/blessed/; |
20a4dd98 |
604 | use MRO::Compat; |
38017482 |
605 | |
606 | sub uri_for { |
b7c570ac |
607 | my $c = shift; |
38017482 |
608 | my $uri = $c->next::method(@_); |
78170776 |
609 | $c->log->warn( 'uri_for with non action: ', join(', ', @_), ) |
610 | if (!blessed($_[0]) || !$_[0]->isa('Catalyst::Action')); |
38017482 |
611 | return $uri; |
612 | } |
613 | |
614 | 1; |
615 | |
b7c570ac |
616 | This would override Catalyst's C<uri_for> method and emit a C<warn> |
78170776 |
617 | log entry containing the arguments to uri_for. |
618 | |
619 | Please note this is not a practical example, as string URLs are fine for |
620 | static content etc. |
621 | |
622 | A simple example like this is actually better as a L<Moose> role, for example: |
623 | |
624 | package CatalystX::UriforUndefWarning; |
625 | use Moose::Role; |
626 | use namespace::clean -except => 'meta'; |
627 | |
628 | after 'uri_for' => sub { |
629 | my ($c, $arg) = @_; |
630 | $c->log->warn( 'uri_for with non action: ', join(', ', @_), ) |
631 | if (!blessed($_[0]) || !$_[0]->isa('Catalyst::Action')); |
632 | return $uri; |
fa025310 |
633 | }; |
38017482 |
634 | |
635 | =head2 Factory components with COMPONENT() |
636 | |
b7c570ac |
637 | Every component inheriting from L<Catalyst::Component> contains a |
638 | C<COMPONENT> method. It is used on application startup by |
639 | C<setup_components> to instantiate the component object for the |
640 | Catalyst application. By default, this will merge the components own |
641 | C<config>uration with the application wide overrides and call the |
642 | class' C<new> method to return the component object. |
38017482 |
643 | |
b7c570ac |
644 | You can override this method and do and return whatever you want. |
fa025310 |
645 | However, you should use L<Class::C3> (via L<MRO::Compat>) to forward |
646 | to the original C<COMPONENT> method to merge the configuration of |
20a4dd98 |
647 | your component. |
38017482 |
648 | |
649 | Here is a stub C<COMPONENT> method: |
650 | |
651 | package CatalystX::Component::Foo; |
652 | use strict; |
653 | use base 'Catalyst::Component'; |
654 | |
20a4dd98 |
655 | use MRO::Compat; |
38017482 |
656 | |
657 | sub COMPONENT { |
658 | my $class = shift; |
a70cede4 |
659 | # Note: $app is like $c, but since the application isn't fully |
660 | # initialized, we don't want to call it $c yet. $config |
661 | # is a hashref of config options possibly set on this component. |
662 | my ($app, $config) = @_; |
663 | |
664 | # Do things here before instantiation |
665 | $new = $class->next::method(@_); |
666 | # Do things to object after instantiation |
667 | return $new; |
38017482 |
668 | } |
669 | |
670 | The arguments are the class name of the component, the class name of |
b7c570ac |
671 | the application instantiating the component, and a hash reference with |
672 | the controller's configuration. |
38017482 |
673 | |
b7c570ac |
674 | You are free to re-bless the object, instantiate a whole other |
675 | component or really do anything compatible with Catalyst's |
676 | expectations on a component. |
38017482 |
677 | |
fa025310 |
678 | For more information, please see |
679 | L<Catalyst::Component/"COMPONENT($c,$arguments)">. |
38017482 |
680 | |
681 | =head1 SEE ALSO |
682 | |
b7c570ac |
683 | L<Catalyst>, L<Catalyst::Manual::Actions>, L<Catalyst::Component> |
38017482 |
684 | |
685 | =head1 AUTHOR |
686 | |
1972ebdd |
687 | Robert Sedlacek C<< <rs@474.at> >> |
688 | |
689 | Jonathan Rockway C<< <jrockway@cpan.org> >> |
38017482 |
690 | |
691 | =head1 LICENSE AND COPYRIGHT |
692 | |
b7c570ac |
693 | This document is free, you can redistribute it and/or modify it under |
38017482 |
694 | the same terms as Perl itself. |
695 | |
696 | =cut |
697 | |