5 Catalyst::RouteMatching - How Catalyst maps an incoming URL to actions in controllers.
9 This is a WIP document intended to help people understand the logic that L<Catalyst>
10 uses to determine how to match in incoming request to an action (or action chain)
13 =head2 Request to Controller/Action Matching
15 L<Catalyst> maps requests to action using a 'longest path wins' approach. That means
16 that if the request is '/foo/bar/baz' That means the action 'baz' matches:
18 package MyApp::Controller::Foo;
21 use MooseX::MethodAttributes
23 extends 'Catalyst::Controller';
25 sub bar :Path('bar') Args(1) { ...}
26 sub baz :Path('bar/baz') Args(0) { ... }
28 Path length matches take precidence over all other types of matches (included HTTP
29 Method, Scheme, etc.). The same holds true for Chained actions. Generally the
30 chain that matches the most PathParts wins.
32 =head2 Args(N) versus Args
34 'Args' matches any number of args. Because this functions as a sort of catchall, we
35 treat 'Args' as the lowest precedence of any Args(N) when N is 0 to infinity. An
36 action with 'Args' always get the last chance to match.
38 =head2 When two or more actions match a given Path
40 Sometimes two or more actions match the same path and all have the same pathpart
43 package MyApp::Controller::Root;
46 use MooseX::MethodAttributes
48 extends 'Catalyst::Controller';
50 sub root :Chained(/) CaptureArgs(0) { }
52 sub one :Chained(root) PathPart('') Args(0) { }
53 sub two :Chained(root) PathPart('') Args(0) { }
54 sub three :Chained(root) PathPart('') Args(0) { }
56 __PACKAGE__->meta->make_immutable;
58 In this case the last defined action wins (for the example that is action 'three').
60 This is most common to happen when you are using action matching beyond paths, such as
61 when using method matching:
63 package MyApp::Controller::Root;
66 use MooseX::MethodAttributes
68 extends 'Catalyst::Controller';
70 sub root :Chained(/) CaptureArgs(0) { }
72 sub any :Chained(root) PathPart('') Args(0) { }
73 sub get :GET Chained(root) PathPart('') Args(0) { }
75 __PACKAGE__->meta->make_immutable;
77 In the above example GET /root could match both actions. In this case you should define
78 your 'catchall' actions higher in the controller.
80 =head2 Type Constraints in Args and Capture Args
82 Beginning in Version 5.90090+ you may use L<Moose>, L<MooseX::Types> or L<Type::Tiny>
83 type constraints to futher declare allowed matching for Args or CaptureArgs. Here
86 package MyApp::Controller::User;
89 use MooseX::MethodAttributes;
91 extends 'Catalyst::Controller';
93 sub find :Path('') Args('Int') {
94 my ($self, $c, $int) = @_;
97 __PACKAGE__->meta->make_immutable;
99 In this case the incoming request "http://localhost:/user/100" would match the action
100 C<find> but "http://localhost:/user/not_a_number" would not. You may find declaring
101 constraints in this manner aids with debugging, automatic generation of documentation
102 and reducing the amount of manual checking you might need to do in your actions. For
103 example if the argument in the given action was going to be used to lookup a row
104 in a database, if the matching field expected an integer, a string might cause a database
105 exception, prompting you to add additional checking of the argument prior to using it.
106 In general it is hoped this feature can lead to reduced validation boilerplate and more
107 easily understood and declarative actions.
109 More than one argument may be added by comma separating your type constraint names, for
112 use Types::Standard qw/Int Str/;
114 sub find :Path('') Args(Int,Int,Str) {
115 my ($self, $c, $int1, $int2, $str) = @_;
118 Would require three arguments, an integer, integer and a string. Note in this example we
119 constrained the args using imported types via L<Types::Standard>. Although you may use
120 stringy Moose types, we recommend imported types since this is less ambiguous to your readers.
121 If you want to use Moose stringy types. you must quote them (either "Int" or 'Int' is fine).
123 Conversely, you should not quote types that are imported!
125 =head3 Using type constraints in a controller
127 By default L<Catalyst> allows all the standard, built-in, named type constraints that come
128 bundled with L<Moose>. However it is trivial to create your own Type constraint libraries
129 and export them to a controller that wishes to use them. We recommend using L<Type::Tiny> or
130 L<MooseX::Types> for this. Here is an example using some extended type constraints via
131 the L<Types::Standard> library that is packaged with L<Type::Tiny>:
133 package MyApp::Controller::User;
136 use MooseX::MethodAttributes;
137 use Types::Standard qw/StrMatch Int/;
139 extends 'Catalyst::Controller';
141 sub looks_like_a_date :Path('') Args(StrMatch[qr{\d\d-\d\d-\d\d}]) {
142 my ($self, $c, $int) = @_;
145 __PACKAGE__->meta->make_immutable;
147 This would match URLs like "http://localhost/user/11-11-2015" for example. If you've been
148 missing the old RegExp matching, this can emulate a good chunk of that ability, and more.
150 A tutorial on how to make custom type libraries is outside the scope of this document. I'd
151 recommend looking at the copious documentation in L<Type::Tiny> or in L<MooseX::Types> if
152 you prefer that system. The author recommends L<Type::Tiny> if you are unsure which to use.
154 =head3 Match order when more than one Action matches a path.
156 As previously described, L<Catalyst> will match 'the longest path', which generally means
157 that named path / path_parts will take precidence over Args or CaptureArgs. However, what
158 will happen if two actions match the same path with equal args? For example:
160 sub an_int :Path(user) Args(Int) {
163 sub an_any :Path(user) Args(1) {
166 In this case L<Catalyst> will check actions starting from the LAST one defined. Generally
167 this means you should put your most specific action rules LAST and your 'catch-alls' first.
168 In the above example, since Args(1) will match any argument, you will find that that 'an_int'
169 action NEVER gets hit. You would need to reverse the order:
171 sub an_any :Path(user) Args(1) {
174 sub an_int :Path(user) Args(Int) {
177 Now requests that match this path would first hit the 'an_int' action and will check to see if
178 the argument is an integer. If it is, then the action will execute, otherwise it will pass and
179 the dispatcher will check the next matching action (in this case we fall thru to the 'an_any'
182 =head3 Type Constraints and Chained Actions
184 Using type constraints in Chained actions works the same as it does for Path and Local or Global
185 actions. The only difference is that you may declare type constraints on CaptureArgs as
186 well as Args. For Example:
188 use Types::Standard qw/Int Tuple/;
190 sub chain_base :Chained(/) CaptureArgs(1) { }
192 sub any_priority_chain :GET Chained(chain_base) PathPart('') Args(1) { }
194 sub int_priority_chain :Chained(chain_base) PathPart('') Args(Int) { }
196 sub link_any :Chained(chain_base) PathPart('') CaptureArgs(1) { }
198 sub any_priority_link_any :Chained(link_any) PathPart('') Args(1) { }
200 sub int_priority_link_any :Chained(link_any) PathPart('') Args(Int) { }
202 sub link_int :Chained(chain_base) PathPart('') CaptureArgs(Int) { }
204 sub any_priority_link :Chained(link_int) PathPart('') Args(1) { }
206 sub int_priority_link :Chained(link_int) PathPart('') Args(Int) { }
208 sub link_int_int :Chained(chain_base) PathPart('') CaptureArgs(Int,Int) { }
210 sub any_priority_link2 :Chained(link_int_int) PathPart('') Args(1) { }
212 sub int_priority_link2 :Chained(link_int_int) PathPart('') Args(Int) { }
214 sub link_tuple :Chained(chain_base) PathPart('') CaptureArgs(Tuple[Int,Int,Int]) { }
216 sub any_priority_link3 :Chained(link_tuple) PathPart('') Args(1) { }
218 sub int_priority_link3 :Chained(link_tuple) PathPart('') Args(Int) { }
220 These chained actions migth create match tables like the following:
222 [debug] Loaded Chained actions:
223 .-------------------------------------+--------------------------------------.
224 | Path Spec | Private |
225 +-------------------------------------+--------------------------------------+
226 | /chain_base/*/* | /chain_base (1) |
227 | | => GET /any_priority_chain (1) |
228 | /chain_base/*/*/* | /chain_base (1) |
229 | | -> /link_int (Int) |
230 | | => /any_priority_link (1) |
231 | /chain_base/*/*/*/* | /chain_base (1) |
232 | | -> /link_int_int (Int,Int) |
233 | | => /any_priority_link2 (1) |
234 | /chain_base/*/*/*/*/* | /chain_base (1) |
235 | | -> /link_tuple (Tuple[Int,Int,Int]) |
236 | | => /any_priority_link3 (1) |
237 | /chain_base/*/*/* | /chain_base (1) |
238 | | -> /link_any (1) |
239 | | => /any_priority_link_any (1) |
240 | /chain_base/*/*/*/*/*/* | /chain_base (1) |
241 | | -> /link_tuple (Tuple[Int,Int,Int]) |
242 | | -> /link2_int (UserId) |
243 | | => GET /finally (Int) |
244 | /chain_base/*/*/*/*/*/... | /chain_base (1) |
245 | | -> /link_tuple (Tuple[Int,Int,Int]) |
246 | | -> /link2_int (UserId) |
247 | | => GET /finally2 (...) |
248 | /chain_base/*/* | /chain_base (1) |
249 | | => /int_priority_chain (Int) |
250 | /chain_base/*/*/* | /chain_base (1) |
251 | | -> /link_int (Int) |
252 | | => /int_priority_link (Int) |
253 | /chain_base/*/*/*/* | /chain_base (1) |
254 | | -> /link_int_int (Int,Int) |
255 | | => /int_priority_link2 (Int) |
256 | /chain_base/*/*/*/*/* | /chain_base (1) |
257 | | -> /link_tuple (Tuple[Int,Int,Int]) |
258 | | => /int_priority_link3 (Int) |
259 | /chain_base/*/*/* | /chain_base (1) |
260 | | -> /link_any (1) |
261 | | => /int_priority_link_any (Int) |
262 '-------------------------------------+--------------------------------------'
264 As you can see the same general path could be matched by various action chains. In this case
265 the rule described in the previous section should be followed, which is that L<Catalyst>
266 will start with the last defined action and work upward. For example the action C<int_priority_chain>
267 would be checked before C<any_priority_chain>. The same applies for actions that are midway links
268 in a longer chain. In this case C<link_int> would be checked before C<link_any>. So as always we
269 recommend that you place you priority or most constrainted actions last and you least or catch-all
272 Although this reverse order checking may seen counter intuitive it does have the added benefit that
273 when inheriting controllers any new actions added would take check precedence over those in your
274 parent controller or consumed role.
276 Please note that your declared type constraint names will now appear in the debug console.
280 John Napiorkowski L<jjnapiork@cpan.org|email:jjnapiork@cpan.org>