1Dancer2::Cookbook(3) User Contributed Perl Documentation Dancer2::Cookbook(3)
2
6 Dancer2::Cookbook - Example-driven quick-start to the Dancer2 web
7 framework
8
10 version 0.300004
11
13 A quick-start guide with examples to get you up and running with the
14 Dancer2 web framework. This document will be twice as useful if you
15 finish reading the manual (Dancer2::Manual) first, but that is not
16 required... :-)
17
19 A simple Dancer2 web app
20 Dancer2 has been designed to be easy to work with - it's trivial to
21 write a simple web app, but still has the power to work with larger
22 projects. To start with, let's make an incredibly simple "Hello World"
23 example:
24 #!/usr/bin/env perl
26 use Dancer2;
28 get '/hello/:name' => sub {
30 return "Why, hello there " . route_parameters->get('name');
31 };
32 dance;
34 Yes - the above is a fully-functioning web app; running that script
36 will launch a webserver listening on the default port (3000). Now you
37 can make a request:
38 $ curl http://localhost:3000/hello/Bob
40 Why, hello there Bob
41 and it will say hello. The ":name" part is a named parameter within the
43 route specification, whose value is made available through
44 "route_parameters".
45 Note that you don't need to use the "strict" and "warnings" pragmas;
47 they are already loaded by Dancer2.
48 Default Route
50 In case you want to avoid a 404 error, or handle multiple routes in the
51 same way and you don't feel like configuring all of them, you can set
52 up a default route handler.
53 The default route handler will handle any request that doesn't get
55 served by any other route.
56 All you need to do is set up the following route as the last route:
58 any qr{.*} => sub {
60 status 'not_found';
61 template 'special_404', { path => request->path };
62 };
63 Then you can set up the template like so:
65 You tried to reach [% path %], but it is unavailable at the moment.
67 Please try again or contact us at <contact@example.com>.
69 Using the "auto_page" feature for automatic route creation
71 For simple "static" pages you can simply enable the "auto_page" config
72 setting; this means you don't need to declare a route handler for those
73 pages; if a request is for "/foo/bar", Dancer2 will check for a
74 matching view (e.g. "/foo/bar.tt") and render it with the default
75 layout, if found. For full details, see the documentation for the
76 auto_page setting.
77 Simplifying AJAX queries with the Ajax plugin
79 As an AJAX query is just an HTTP query, it's similar to a GET or POST
80 route. You may ask yourself why you may want to use the "ajax" keyword
81 (from the Dancer2::Plugin::Ajax plugin) instead of a simple "get".
82 Let's say you have a path like "/user/:user" in your application. You
84 may want to be able to serve this page with a layout and HTML content.
85 But you may also want to be able to call this same url from a
86 javascript query using AJAX.
87 So, instead of having the following code:
89 get '/user/:user' => sub {
91 if ( request->is_ajax ) {
92 # create xml, set headers to text/xml, blablabla
93 header( 'Content-Type' => 'text/xml' );
94 header( 'Cache-Control' => 'no-store, no-cache, must-revalidate' );
95 to_xml({...})
96 } else {
97 template users => {...}
98 }
99 };
100 you can have
102 ajax '/user/:user' => sub {
104 to_xml( {...}, RootName => undef );
105 }
106 and
108 get '/user/:user' => sub {
110 template users => {...}
111 }
112 Because it's an AJAX query, you know you need to return XML content, so
114 the content type of the response is set for you.
115 Example: Feeding graph data through AJAX
117 Let us assume we are building an application that uses a plotting
119 library to generate a graph and expects to get its data, which is in
120 the form of word count from an AJAX call.
121 For the graph, we need the url /data to return a JSON representation of
123 the word count data. Dancer in fact has a "encode_json()" function that
124 takes care of the JSON encapsulation.
125 get '/data' => sub {
127 open my $fh, '<', $count_file;
128 my %contestant;
130 while (<$fh>) {
131 chomp;
132 my ( $date, $who, $count ) = split '\s*,\s*';
133 my $epoch = DateTime::Format::Flexible->parse_datetime($date)->epoch;
135 my $time = 1000 * $epoch;
136 $contestant{$who}{$time} = $count;
137 }
138 my @json; # data structure that is going to be JSONified
140 while ( my ( $peep, $data ) = each %contestant ) {
142 push @json, {
143 label => $peep,
144 hoverable => \1, # so that it becomes JavaScript's 'true'
145 data => [ map { [ $_, $data->{$_} ] }
146 sort { $a <=> $b }
147 keys %$data ],
148 };
149 }
150 my $beginning = DateTime::Format::Flexible->parse_datetime( "2010-11-01")->epoch;
152 my $end = DateTime::Format::Flexible->parse_datetime( "2010-12-01")->epoch;
153 push @json, {
155 label => 'de par',
156 data => [
157 [$beginning * 1000, 0],
158 [ DateTime->now->epoch * 1_000,
159 50_000
160 * (DateTime->now->epoch - $beginning)
161 / ($end - $beginning)
162 ]
163 ],
164 };
166 encode_json( \@json );
168 };
169 For more serious AJAX interaction, there's also Dancer2::Plugin::Ajax
171 that adds an ajax route handler to the mix.
172 Because it's an AJAX query, you know you need to return XML content, so
174 the content type of the response is set for you.
175 Using the prefix feature to split your application
177 For better maintainability, you may want to separate some of your
178 application components into different packages. Let's say we have a
179 simple web app with an admin section and want to maintain this in a
180 different package:
181 package myapp;
183 use Dancer2;
184 use myapp::admin;
185 prefix undef;
187 get '/' => sub {...};
189 1;
191 package myapp::admin;
193 use Dancer2 appname => 'myapp';
194 prefix '/admin';
196 get '/' => sub {...};
198 1;
200 The following routes will be generated for us:
202 - get /
204 - get /admin/
205 - head /
206 - head /admin/
207 By default, a separate application is created for every package that
209 uses Dancer2. The "appname" tag is used to collect routes and hooks
210 into a single Dancer2 application. In the above example, "appname =>
211 'myapp'" adds the routes from "myapp::admin" to the routes of the app
212 "myapp".
213 When using multiple applications please ensure that your path
215 definitions do not overlap. For example, if using a default route as
216 described above, once a request is matched to the default route then no
217 further routes (or applications) would be reached.
218 Delivering custom error pages
220 At the Core
221 In Dancer2, creating new errors is done by creating a new
223 Dancer2::Core::Error
224 my $oopsie = Dancer2::Core::Error->new(
226 status => 418,
227 message => "This is the Holidays. Tea not acceptable. We want eggnog.",
228 app => $app,
229 )
230 If not given, the status code defaults to a 500, there is no need for a
232 message if we feel taciturn, and while the $app (which is a
233 Dancer2::Core::App object holding all the pieces of information related
234 to the current request) is needed if we want to take advantage of the
235 templates, we can also do without.
236 However, to be seen by the end user, we have to populate the
238 Dancer2::Core::Response object with the error's data. This is done via:
239 $oopsie->throw($response);
241 Or, if we want to use the response object already present in the $app
243 (which is usually the case):
244 $oopsie->throw;
246 This populates the status code of the response, sets its content, and
248 throws a halt() in the dispatch process.
249 What it will look like
251 The error object has quite a few ways to generate its content.
253 First, it can be explicitly given
255 my $oopsie = Dancer2::Core::Error->new(
257 content => '<html><body><h1>OMG</h1></body></html>',
258 );
259 If the $context was given, the error will check if there is a template
261 by the name of the status code (so, say you're using Template Toolkit,
262 418.tt) and will use it to generate the content, passing it the error's
263 $message, $status code and $title (which, if not specified, will be the
264 standard http error definition for the status code).
265 If there is no template, the error will then look for a static page (to
267 continue with our example, 418.html) in the public/ directory.
268 And finally, if all of that failed, the error object will fall back on
270 an internal template.
271 Errors in Routes
273 The simplest way to use errors in routes is:
275 get '/xmas/gift/:gift' => sub {
277 die "sorry, we're all out of ponies\n"
278 if route_parameters->get('gift') eq 'pony';
279 };
280 The die will be intercepted by Dancer, converted into an error (status
282 code 500, message set to the dying words) and passed to the response.
283 In the cases where more control is required, "send_error()" is the way
285 to go:
286 get '/glass/eggnog' => sub {
288 send_error "Sorry, no eggnog here", 418;
289 };
290 And if total control is needed:
292 get '/xmas/wishlist' => sub {
294 Dancer2::Core::Error->new(
295 response => response(),
296 status => 406,
297 message => "nothing but coal for you, I'm afraid",
298 template => 'naughty/index',
299 )->throw unless user_was_nice();
300 ...;
302 };
303 Template Toolkit's WRAPPER directive in Dancer2
305 Dancer2 already provides a WRAPPER-like ability, which we call a
306 "layout". The reason we don't use Template Toolkit's WRAPPER (which
307 also makes us incompatible with it) is because not all template systems
308 support it. In fact, most don't.
309 However, you might want to use it, and be able to define META variables
311 and regular Template::Toolkit variables.
312 These few steps will get you there:
314 · Disable the layout in Dancer2
316 You can do this by simply commenting (or removing) the "layout"
318 configuration in the config file.
319 · Use the Template Toolkit template engine
321 Change the configuration of the template to Template Toolkit:
323 # in config.yml
325 template: "template_toolkit"
326 · Tell the Template Toolkit engine which wrapper to use
328 # in config.yml
330 # ...
331 engines:
332 template:
333 template_toolkit:
334 WRAPPER: layouts/main.tt
335 Done! Everything will work fine out of the box, including variables and
337 META variables.
338 However, disabling the internal layout it will also disable the hooks
340 "before_layout_render" and "after_layout_render".
341 Customizing Template Toolkit in Dancer2
343 Please see Dancer2::Template::TemplateToolkit for more details.
344 Accessing configuration information from a separate script
346 You may want to access your webapp's configuration from outside your
347 webapp. You could, of course, use the YAML module of your choice and
348 load your webapps's "config.yml", but chances are that this is not
349 convenient.
350 Use Dancer2 instead. You can simply use the values from "config.yml"
352 and some additional default values:
353 # bin/show_app_config.pl
355 use Dancer2;
356 printf "template: %s\n", config->{'template'}; # simple
357 printf "log: %s\n", config->{'log'}; # undef
358 Note that "config->{log}" should result in an uninitialized warning on
360 a default scaffold since the environment isn't loaded and log is
361 defined in the environment and not in "config.yml". Hence "undef".
362 Dancer2 will load your "config.yml" configuration file along with the
364 correct environment file located in your "environments" directory.
365 The environment is determined by two environment variables in the
367 following order:
368 · DANCER_ENVIRONMENT
370 · PLACK_ENV
372 If neither of those is set, it will default to loading the development
374 environment (typically "$webapp/environment/development.yml").
375 If you wish to load a different environment, you need to override these
377 variables.
378 You can call your script with the environment changed:
380 $ PLACK_ENV=production perl bin/show_app_config.pl
382 Or you can override them directly in the script (less recommended):
384 BEGIN { $ENV{'DANCER_ENVIRONMENT'} = 'production' }
386 use Dancer2;
387 ...
389 Using DBIx::Class
391 DBIx::Class, also known as DBIC, is one of the many Perl ORM (Object
392 Relational Mapper). It is easy to use DBIC in Dancer2 using the
393 Dancer2::Plugin::DBIC.
394 An example
396 This example demonstrates a simple Dancer2 application that allows one
398 to search for authors or books. The application is connected to a
399 database, that contains authors, and their books. The website will have
400 one single page with a form, that allows one to query books or authors,
401 and display the results.
402 Creating the application
404 $ dancer2 -a bookstore
406 To use the Template Toolkit as the template engine, we specify it in
408 the configuration file:
409 # add in bookstore/config.yml
411 template: template_toolkit
412 Creating the view
414 We need a view to display the search form, and below, the results, if
416 any. The results will be fed by the route to the view as an arrayref of
417 results. Each result is a hashref, with a author key containing the
418 name of the author, and a books key containing an arrayref of strings :
419 the books names.
420 # example of a list of results
422 [ { author => 'author 1',
423 books => [ 'book 1', 'book 2' ],
424 },
425 { author => 'author 2',
426 books => [ 'book 3', 'book 4' ],
427 }
428 ]
429 # bookstore/views/search.tt
432 <p>
433 <form action="/search">
434 Search query: <input type="text" name="query" />
435 </form>
436 </p>
437 <br>
438 An example of the view, displaying the search form, and the results, if
440 any:
441 <% IF query.length %>
443 <p>Search query was : <% query %>.</p>
444 <% IF results.size %>
445 Results:
446 <ul>
447 <% FOREACH result IN results %>
448 <li>Author: <% result.author.replace("((?i)$query)", '<b>$1</b>') %>
449 <ul>
450 <% FOREACH book IN result.books %>
451 <li><% book.replace("((?i)$query)", '<b>$1</b>') %>
452 <% END %>
453 </ul>
454 <% END %>
455 <% ELSE %>
456 No result
457 <% END %>
458 <% END %>
459 Creating a Route
461 A simple route, to be added in the bookstore.pm module:
463 # add in bookstore/lib/bookstore.pm
465 get '/search' => sub {
466 my $query = query_parameters->get('query');
467 my @results = ();
468 if ( length $query ) {
470 @results = _perform_search($query);
471 }
472 template search => {
474 query => $query,
475 results => \@results,
476 };
477 };
478 Creating a database
480 We create a SQLite file database:
482 $ sqlite3 bookstore.db
484 CREATE TABLE author(
485 id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
486 firstname text default '' not null,
487 lastname text not null);
488 CREATE TABLE book(
490 id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
491 author INTEGER REFERENCES author (id),
492 title text default '' not null );
493 Now, to populate the database with some data, we use DBIx::Class:
495 # populate_database.pl
497 package My::Bookstore::Schema;
498 use base qw(DBIx::Class::Schema::Loader);
499 package main;
500 my $schema = My::Bookstore::Schema->connect('dbi:SQLite:dbname=bookstore.db');
501 $schema->populate('Author', [
502 [ 'firstname', 'lastname'],
503 [ 'Ian M.', 'Banks' ],
504 [ 'Richard', 'Matheson'],
505 [ 'Frank', 'Herbert' ],
506 ]);
507 my @books_list = (
508 [ 'Consider Phlebas', 'Banks' ],
509 [ 'The Player of Games', 'Banks' ],
510 [ 'Use of Weapons', 'Banks' ],
511 [ 'Dune', 'Herbert' ],
512 [ 'Dune Messiah', 'Herbert' ],
513 [ 'Children of Dune', 'Herbert' ],
514 [ 'The Night Stalker', 'Matheson' ],
515 [ 'The Night Strangler', 'Matheson' ],
516 );
517 # transform author names into ids
518 $_->[1] = $schema->resultset('Author')->find({ lastname => $_->[1] })->id
519 foreach (@books_list);
520 $schema->populate('Book', [
521 [ 'title', 'author' ],
522 @books_list,
523 ]);
524 Then run it in the directory where bookstore.db sits:
526 perl populate_database.db
528 Using Dancer2::Plugin::DBIC
530 There are 2 ways of configuring DBIC to understand how the data is
532 organized in your database:
533 · Use auto-detection
535 The configuration file needs to be updated to indicate the use of
537 the Dancer2::Plugin::DBIC plugin, define a new DBIC schema called
538 bookstore and to indicate that this schema is connected to the
539 SQLite database we created.
540 # add in bookstore/config.yml
542 plugins:
543 DBIC:
544 bookstore:
545 dsn: "dbi:SQLite:dbname=bookstore.db"
546 Now, "_perform_search" can be implemented using
548 Dancer2::Plugin::DBIC. The plugin gives you access to an additional
549 keyword called schema, which you give the name of schema you want
550 to retrieve. It returns a "DBIx::Class::Schema::Loader" which can
551 be used to get a resultset and perform searches, as per standard
552 usage of DBIX::Class.
553 # add in bookstore/lib/bookstore.pm
555 sub _perform_search {
556 my ($query) = @_;
557 my $bookstore_schema = schema 'bookstore';
558 my @results;
559 # search in authors
560 my @authors = $bookstore_schema->resultset('Author')->search({
561 -or => [
562 firstname => { like => "%$query%" },
563 lastname => { like => "%$query%" },
564 ]
565 });
566 push @results, map {
567 { author => join(' ', $_->firstname, $_->lastname),
568 books => [],
569 }
570 } @authors;
571 my %book_results;
572 # search in books
573 my @books = $bookstore_schema->resultset('Book')->search({
574 title => { like => "%$query%" },
575 });
576 foreach my $book (@books) {
577 my $author_name = join(' ', $book->author->firstname, $book->author->lastname);
578 push @{$book_results{$author_name}}, $book->title;
579 }
580 push @results, map {
581 { author => $_,
582 books => $book_results{$_},
583 }
584 } keys %book_results;
585 return @results;
586 }
587 · Use home made schema classes
589 The DBIx::Class::MooseColumns lets you write the DBIC schema
591 classes using Moose. The schema classes should be put in a place
592 that Dancer2 will find. A good place is in bookstore/lib/.
593 Once your schema classes are in place, all you need to do is modify
595 config.yml to specify that you want to use them, instead of the
596 default auto-detection method:
597 # change in bookstore/config.yml
599 plugins:
600 DBIC:
601 bookstore:
602 schema_class: My::Bookstore::Schema
603 dsn: "dbi:SQLite:dbname=bookstore.db"
604 Starting the application: Our bookstore lookup application can now
606 be started using the built-in server:
607 # start the web application
609 plackup bin/app.psgi
610 Authentication
612 Writing a form for authentication is simple: we check the user
613 credentials on a request and decide whether to continue or redirect
614 them to a form. The form allows them to submit their username and
615 password and we save that and create a session for them so when they
616 now try the original request, we recognize them and allow them in.
617 Basic Application
619 The application is fairly simple. We have a route that needs
621 authentication, we have a route for showing the login page, and we have
622 a route for posting login information and creating a session.
623 package MyApp;
625 use Dancer2;
626 get '/' => sub {
628 session('user')
629 or redirect('/login');
630 template index => {};
632 };
633 get '/login' => sub {
635 template login => {};
636 };
637 post '/login' => sub {
639 my $username = query_parameters->get('username');
640 my $password = query_parameters->get('password');
641 my $redir_url = query_parameters->get('redirect_url') || '/login';
642 $username eq 'john' && $password eq 'correcthorsebatterystaple'
644 or redirect $redir_url;
645 session user => $username;
647 redirect $redir_url;
648 };
649 Tiny Authentication Helper
651 Dancer2::Plugin::Auth::Tiny allows you to abstract away not only the
653 part that checks whether the session exists, but to also generate a
654 redirect with the right path and return URL.
655 We simply have to define what routes needs a login using Auth::Tiny's
657 "needs" keyword.
658 get '/' => needs login => sub {
660 template index => {};
661 };
662 It creates a proper return URL using "uri_for" and the address from
664 which the user arrived.
665 We can thus decorate all of our private routes to require
667 authentication in this manner. If a user does not have a session, it
668 will automatically forward it to /login, in which we would render a
669 form for the user to send a login request.
670 Auth::Tiny even provides a new parameter, "return_url", which can be
672 used to send the user back to their original requested path.
673 Password Hashing
675 Dancer2::Plugin::Passphrase provides a simple passwords-as-objects
677 interface with sane defaults for hashed passwords which you can use in
678 your web application. It uses bcrypt as the default but supports
679 anything the Digest interface does.
680 Assuming we have the original user-creation form submitting a username
682 and password:
683 package MyApp;
685 use Dancer2;
686 use Dancer2::Plugin::Passphrase;
687 post '/register' => sub {
688 my $username = query_parameters->get('username');
689 my $password = passphrase(
690 query_parameters->get('password')
691 )->generate;
692 # $password is now a hashed password object
694 save_user_in_db( $username, $password->rfc2307 );
695 template registered => { success => 1 };
697 };
698 We can now add the POST method for verifying that username and
700 password:
701 post '/login' => sub {
703 my $username = query_parameters->get('username');
704 my $password = query_parameters->get('password');
705 my $saved_pass = fetch_password_from_db($username);
706 if ( passphrase($password)->matches($saved_pass) ) {
708 session user => $username;
709 redirect query_parameters->get('return_url') || '/';
710 }
711 # let's render instead of redirect...
713 template login => { error => 'Invalid username or password' };
714 };
715 Writing a REST application
717 With Dancer2, it's easy to write REST applications. Dancer2 provides
718 helpers to serialize and deserialize for the following data formats:
719 JSON
721 YAML
722 XML
723 Data::Dumper
724 To activate this feature, you only have to set the "serializer" setting
726 to the format you require, for instance in your config file:
727 serializer: JSON
729 Or directly in your code:
731 set serializer => 'JSON';
733 From now, all hashrefs or arrayrefs returned by a route will be
735 serialized to the format you chose, and all data received from POST or
736 PUT requests will be automatically deserialized.
737 get '/hello/:name' => sub {
739 # this structure will be returned to the client as
740 # {"name":"$name"}
741 return { name => query_parameters->get('name') };
742 };
743 It's possible to let the client choose which serializer to use. For
745 this, use the "mutable" serializer, and an appropriate serializer will
746 be chosen from the "Content-Type" header.
747 It's also possible to return a custom error using the send_error
749 keyword. When you don't use a serializer, the "send_error" function
750 will take a string as first parameter (the message), and an optional
751 HTTP code. When using a serializer, the message can be a string, an
752 arrayref or a hashref:
753 get '/hello/:name' => sub {
755 if (...) {
756 send_error("you can't do that");
757 # or
758 send_error({reason => 'access denied', message => "no"});
759 }
760 };
761 The content of the error will be serialized using the appropriate
763 serializer.
764 Using the serializer
766 Serializers essentially do two things:
767 · Deserialize incoming requests
769 When a user makes a request with serialized input, the serializer
771 automatically deserializes it into actual input parameters.
772 · Serialize outgoing responses
774 When you return a data structure from a route, it will
776 automatically serialize it for you before returning it to the user.
777 Configuring
779 In order to configure a serializer, you just need to pick which format
781 you want for encoding/decoding (e.g. JSON) and set it up using the
782 "serializer" configuration keyword.
783 It is recommended to explicitly add it in the actual code instead of
785 the configuration file so it doesn't apply automatically to every app
786 that reads the configuration file (unless that's what you want):
787 package MyApp;
789 use Dancer2;
790 set serializer => 'JSON'; # Dancer2::Serializer::JSON
791 ...
793 Using
795 Now that we have a serializer set up, we can just return data
797 structures:
798 get '/' => sub {
800 return { resources => \%resources };
801 };
802 When we return this data structure, it will automatically be serialized
804 into JSON. No other code is necessary.
805 We also now receive requests in JSON:
807 post '/:entity/:id' => sub {
809 my $entity = route_parameters->get('entity');
810 my $id = route_parameters->get('id');
811 # input which was sent serialized
813 my $user = body_parameters->get('user');
814 ...
816 };
817 We can now make a serialized request:
819 $ curl -X POST http://ourdomain/person/16 -d '{"user":"sawyer_x"}'
821 App-specific feature
823 Serializers are engines. They affect a Dancer Application, which means
825 that once you've set a serializer, all routes within that package will
826 be serialized and deserialized. This is how the feature works.
827 As suggested above, if you would like to have both, you need to create
829 another application which will not be serialized.
830 A common usage for this is an API providing serialized endpoints (and
832 receiving serialized requests) and providing rendered pages.
833 # MyApp.pm
835 package MyApp;
836 use Dancer2;
837 # another useful feature:
839 set auto_page => 1;
840 get '/' => sub { template 'index' => {...} };
842 # MyApp/API.pm
844 package MyApp::API;
845 use Dancer2;
846 set serializer => 'JSON'; # or any other serializer
847 get '/' => sub { +{ resources => \%resources, ... } };
849 # user-specific routes, for example
851 prefix '/users' => sub {
852 get '/view' => sub {...};
853 get '/view/:id' => sub {...};
854 put '/add' => sub {...}; # automatically deserialized params
855 };
856 ...
858 Then those will be mounted together for a single app:
860 # handler: app.pl:
862 use MyApp;
863 use MyApp::API;
864 use Plack::Builder;
865 builder {
867 mount '/' => MyApp->to_app;
868 mount '/api' => MyApp::API->to_app;
869 };
870 If you want use redirect from a mounted package to the application's
872 root URI, Dancer2::Plugin::RootURIFor makes this possible:
873 package OurWiki;
875 use Dancer;
876 use Dancer2::Plugin::RootURIFor;
877 get '/:some_path' => sub {
879 redirect root_uri_for('/');
880 }
881 An example: Writing API interfaces
883 This example demonstrates an app that makes a request to a weather API
885 and then displays it dynamically in a web page.
886 Other than Dancer2 for defining routes, we will use HTTP::Tiny to make
888 the weather API request, JSON to decode it from JSON format, and
889 finally File::Spec to provide a fully-qualified path to our template
890 engine.
891 use JSON;
893 use Dancer2;
894 use HTTP::Tiny;
895 use File::Spec;
896 Configuration
898 We use the Template::Toolkit template system for this app. Dancer
900 searches for our templates in our views directory, which defaults to
901 views directory in our current directory. Since we want to put our
902 template in our current directory, we will configure that. However,
903 Template::Toolkit does not want us to provide a relative path without
904 configuring it to allow it. This is a security issue. So, we're using
905 File::Spec to create a full path to where we are.
906 We also unset the default layout, so Dancer won't try to wrap our
908 template with another one. This is a feature in Dancer to allow you to
909 wrap your templates with a layout when your templating system doesn't
910 support it. Since we're not using a layout here, we don't need it.
911 set template => 'template_toolkit'; # set template engine
913 set layout => undef; # disable layout
914 set views => File::Spec->rel2abs('.'); # full path to views
915 Now, we define our URL:
917 my $url = 'http://api.openweathermap.org/data/2.5/weather?id=5110629&units=imperial';
919 Route
921 We will define a main route which, upon a request, will fetch the
923 information from the weather API, decode it, and then display it to the
924 user.
925 Route definition:
927 get '/' => sub {
929 ...
930 };
931 Editing the stub of route dispatching code, we start by making the
933 request and decoding it:
934 # fetch data
936 my $res = HTTP::Tiny->new->get($url);
937 # decode request
939 my $data = decode_json $res->{'content'};
940 The data is not just a flat hash. It's a deep structure. In this
942 example, we will filter it for only the simple keys in the retrieved
943 data:
944 my $metrics = { map +(
946 ref $data->{$_} ? () : ( $_ => $data->{$_} )
947 ), keys %{$data} };
948 All that is left now is to render it:
950 template index => { metrics => $metrics };
952
954 Turning off warnings
955 The "warnings" pragma is already used when one loads Dancer2. However,
956 if you really do not want the "warnings" pragma (for example, due to an
957 undesired warning about use of undef values), add a "no warnings"
958 pragma to the appropriate block in your module or psgi file.
959
961 Dancer Core Developers
962
964 This software is copyright (c) 2020 by Alexis Sukrieh.
965 This is free software; you can redistribute it and/or modify it under
967 the same terms as the Perl 5 programming language system itself.
968perl v5.32.0 2020-07-28 Dancer2::Cookbook(3)