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Re: Framework for making Moose-compatible object from json

by haj (Vicar)
on Aug 20, 2022 at 19:30 UTC ( [id://11146270]=note: print w/replies, xml ) Need Help??


in reply to Framework for making Moose-compatible object from json

A difference between a JSON data structure and a Perl object is that Perl objects are blessed to a class. In your other comment you write that the Class hierarchy is predefined. So it appears the actual task is to find the correct class for each of the references you find in your JSON data structure. But then, there's the phrase adds object specific methods, some internal logic which creates some friction. If the class hierarchy is predefined, then every object should be happy with the methods this class provides, and the user code should already contain the internal logic.

Maybe what you need is just a set of rules which map parts of the structure to their corresponding class. Users of MooseX::DOM create a DOM to define these rules for XML data. With MooseX::Role::JSONObject you can convert JSON data to objects if the JSON data itself contain the rules, which they do if the JSON data have been created by the very same module. That doesn't seem to be the case for your JSON data.

There is a chance that Moose itself is all the "framework" you need: If your classes are written as Moose-classes matching the JSON hashes, then you can just feed the JSON hash to the class constructor. The attribute declaration in the class can then use coercion to turn JSON hash references to objects if an attribute is supposed to be an object. Or, slightly more messy, you can use the BUILDARGS methods.

Here's some code, based on your JSON example:

use 5.028; use warnings; package MyCoolRestObject; use Moose; use Moose::Util::TypeConstraints; has body_raw => ( is => 'ro' ); has url => ( is => 'ro' ); has datetime => ( is => 'ro' ); has entry_id => ( is => 'ro' ); has subject_html => ( is => 'ro' ); coerce 'MyCoolRestObject::Poster' => from 'HashRef' => via { MyCoolRestObject::Poster->new(%$_) }; has poster => ( is => 'ro', isa => 'MyCoolRestObject::Poster', coerce => 1, ); coerce 'MyCoolRestObject::Icon' => from 'HashRef' => via { MyCoolRestObject::Icon->new(%$_) }; has icon => ( is => 'ro', isa => 'MyCoolRestObject::Icon', coerce => 1, ); has subject_raw => ( is => 'ro' ); has body_html => ( is => 'ro' ); # -------------------------------------------------------------------- +-- package MyCoolRestObject::Icon; use Moose; has url => ( is => 'ro' ); has comment => ( is => 'ro' ); has picid => ( is => 'ro' ); has keywords => ( is => 'ro' ); has username => ( is => 'ro' ); # -------------------------------------------------------------------- +-- package MyCoolRestObject::Poster; use Moose; has display_name => ( is => 'ro' ); has user_name => ( is => 'ro' ); # -------------------------------------------------------------------- +-- package main; use JSON::PP; use Data::Dump qw/dump/; $/ = undef; my $json = decode_json <DATA>; my $obj = MyCoolRestObject->new(%$json); print $obj->icon->username; __DATA__ { "body_raw" : "This is <b>Entry 1</b>", "url" : "http://nataraj.nataraj.hack.dreamwidth.net/459.html", "datetime" : "2022-08-20 16:36:00", "entry_id" : 459, "subject_html" : "Entry 1", "poster" : { "display_name" : "nataraj", "username" : "nataraj" }, "icon" : { "url" : "http://www.nataraj.hack.dreamwidth.net/userpic/1/3", "comment" : "4", "picid" : 1, "keywords" : [ "3" ], "username" : "nataraj" }, "subject_raw" : "Entry 1", "body_html" : "This is <b>Entry 1</b>" }

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Re^2: Framework for making Moose-compatible object from json
by nataraj (Sexton) on Aug 21, 2022 at 04:39 UTC
    Maybe what you need is just a set of rules which map parts of the structure to their corresponding class.

    That's exactly what I need. I only did not managed to put it into words properly

    There is a chance that Moose itself is all the "framework" you need

    This looks like a good idea, but it would miss backward serialization (object->json). So you can do something like that:

    my $obj= MyCoolRestObject::UserInfo->new($api->get("/path/to/proper/ +call")); $obj->phone1("+722233344555"); $api->put("path/to/put/call",$obj->as_json);

    So as far as I can get, there is no such mapper for JSON, that would work out of box the same way MooseX::DOM works for XML. And may be I should write it first, and then use it

      And may be I should write it first, and then use it

      There's nothing wrong with that approach, of course. On the other hand, object->JSON conversion isn't all that difficult, so I added it to my example (I also fixed a typo where I had user_name instead of username).

      In my example, the Moose class definition plays the role of the DOM, so you don't need to store class metadata in JSON. JSON does not know about classes, so you need to tell the JSON encoder what to do if it hits an object. To do this, I use the convert_blessed property of the JSON::PP encoder and define a TO_JSON method which just reduces an object to its underlying hash reference.

      A final note before we get to the code: I've been using JSON::PP because it's in Perl core. The code works just as fine with JSON which will use one of the faster XS implementations if they're available.

      use 5.028; use warnings; package MyCoolRestObject; use Moose; use Moose::Util::TypeConstraints; with 'MyCoolRestObject::Serializer'; has body_raw => ( is => 'ro' ); has url => ( is => 'ro' ); has datetime => ( is => 'ro' ); has entry_id => ( is => 'ro' ); has subject_html => ( is => 'ro' ); coerce 'MyCoolRestObject::Poster' => from 'HashRef' => via { MyCoolRestObject::Poster->new(%$_) }; has poster => ( is => 'ro', isa => 'MyCoolRestObject::Poster', coerce => 1, ); coerce 'MyCoolRestObject::Icon' => from 'HashRef' => via { MyCoolRestObject::Icon->new(%$_) }; has icon => ( is => 'ro', isa => 'MyCoolRestObject::Icon', coerce => 1, ); has subject_raw => ( is => 'ro' ); has body_html => ( is => 'ro' ); # -------------------------------------------------------------------- package MyCoolRestObject::Icon; use Moose; with 'MyCoolRestObject::Serializer'; has url => ( is => 'ro' ); has comment => ( is => 'ro' ); has picid => ( is => 'ro' ); has keywords => ( is => 'ro' ); has username => ( is => 'ro' ); # -------------------------------------------------------------------- package MyCoolRestObject::Poster; use Moose; with 'MyCoolRestObject::Serializer'; has display_name => ( is => 'ro' ); has username => ( is => 'ro' ); # -------------------------------------------------------------------- package MyCoolRestObject::Serializer; use Moose::Role; sub TO_JSON { +{ shift->%* } } # -------------------------------------------------------------------- package main; use Cpanel::JSON::XS; $/ = undef; my $json = decode_json <DATA>; # Cpanel::JSON::XS -> Object: my $obj = MyCoolRestObject->new(%$json); say $obj->icon->username; # Object->Cpanel::JSON::XS: my $encoder = Cpanel::JSON::XS->new->utf8->pretty->convert_blessed; my $json_out = $encoder->encode($obj); say $json_out; __DATA__ { "body_raw" : "This is <b>Entry 1</b>", "url" : "http://nataraj.nataraj.hack.dreamwidth.net/459.html", "datetime" : "2022-08-20 16:36:00", "entry_id" : 459, "subject_html" : "Entry 1", "poster" : { "display_name" : "nataraj", "username" : "nataraj" }, "icon" : { "url" : "http://www.nataraj.hack.dreamwidth.net/userpic/1/3", "comment" : "4", "picid" : 1, "keywords" : [ "3" ], "username" : "nataraj" }, "subject_raw" : "Entry 1", "body_html" : "This is <b>Entry 1</b>" }

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