To_json() does not have behave like to_xml builder and block support


#1

Our Rails application needs to support both xml and json formats. In
some cases, we need to return custom XML that spans several objects
and associations. I’ve been able to write custom to_xml methods that
use the builder and block functionality. When trying the same thing
with the to_json method, I failed to get the same result.

Basically to_xml has this signature: to_xml(options = {}, &block).
I’ve perused around and it appears to_json has this signature:
to_json(options = {}). Is there a version of to_json that will yield
to a block
and provide the json builder? Can someone please tell me if I’ve done
something wrong with the code below? Is there is a plugin or newer
version of Rails that will add the same support for to_json that
to_xml supports?

Here is the relevant code

class Conference < ActiveRecord::Base
has_many :courses, :dependent => :destroy
end

class Course < ActiveRecord::Base
belongs_to :conference
has_many :sessions, :dependent => :destroy
has_one :manual

        # just a place holder method so we can serialize it

def pre_requisite
“An open mind”
end
end

class Session < ActiveRecord::Base
belongs_to :courses
has_one :presentation, :dependent=>:destroy

        # just a place holder method so we can serialize it

def maximum_capacity_reached?
false;
end
end

class Presentation < ActiveRecord::Base
belongs_to :session
belongs_to :instructor
end

class Manual < ActiveRecord::Base
belongs_to :course
end

class Instructor < ActiveRecord::Base
end

Now let’s suppose I have a controller that will return the full detail
of a conference and needs all of the related data and will also
serialize some custom methods.
class ConferencesController < ApplicationController

GET /conferences/:id

def show
conference_id = params[:id]

respond_to do |format|
  format.html # unsupported
  format.json {
    render(:json=>Conference.full_json(conference_id))
  }
  format.xml {
    render(:xml=>Conference.full_xml(conference_id))
  }
end

end
end

So I’ve extended the conference class so that it can build this nested
xml along with the result of selective methods on various classes.
this code uses the fact that to_xml has this signature: to_xml(options
= {}, &block)

class Conference < ActiveRecord::Base
has_many :courses, :dependent => :destroy

def slogan
“#{name}: Be here or be in the dark!”
end

def self.full_xml(conference_id)
# ensure we’ve loaded the full structure in the most efficient
manner
conference = Conference.find(conference_id, :include=>{:courses =>
[:manual, {:sessions=>:presentation}]})

# extract detailed hierarchical xml
conference.to_xml do |xml|
  xml.slogan conference.slogan # output the banner

  #iterate courses and any custom methods
  xml.courses{
    conference.courses.each do |course|
      course.to_xml(:builder=>xml, :skip_instruct => true) do |

xml_course|
xml_course.sessions{
#iterate sessions and any custom methods
course.sessions.each do |session|
session.to_xml(:builder=>xml_course, :skip_instruct =>
true)
do |xml_course_session|
xml_course_session.is_at_capacity
session.maximum_capacity_reached?
end
end
}
end
end
}
end
end

def self.full_json(conference_id)
# ensure we’ve loaded the full structure in the most efficient
manner
conference = Conference.find(conference_id, :include=>{:courses =>
[:manual, {:sessions=>:presentation}]})

debugger()

# extract detailed hierarchical xml
conference.to_json do |json|
  json.slogan conference.slogan # output the banner

  #iterate courses and any custom methods
  json.courses{
    conference.courses.each do |course|
      course.to_json(:builder=>json, :skip_instruct => true) do |

json_course|
json_course.sessions{
#iterate sessions and any custom methods
course.sessions.each do |session|
session.to_json(:builder=>json_course, :skip_instruct =>
true)
do |json_course_session|
json_course_session.is_at_capacity
session.maximum_capacity_reached?
end
end
}
end
end
}
end
end
end

When I invoke the method, via http://localhost:3000/conferences/1.xml,
I get the desired generated XML output:

2008-11-04T13:59:41-08:00
1
Ruby Live
2008-11-04T13:59:41-08:00
Ruby Live: Be here or be in the dark!


1
Action Controller: In Depth
2008-11-04T13:59:41-08:00
1
2008-11-04T13:59:41-08:00


1
2008-11-04T13:59:41-08:00
2008-12-04T15:59:41-08:00
1
4
101
2008-12-04T13:59:41-08:00
2008-11-04T13:59:41-08:00
<is_at_capacity>false</is_at_capacity>


1
2008-11-04T13:59:41-08:00
2008-12-05T15:59:41-08:00
2
4
101
2008-12-05T13:59:41-08:00
2008-11-04T13:59:41-08:00
<is_at_capacity>false</is_at_capacity>



+

1
Active Record: In Depth
2008-11-04T13:59:41-08:00
2
2008-11-04T13:59:41-08:00


2
2008-11-04T13:59:41-08:00
2008-12-04T17:59:41-08:00
3
5
201
2008-12-04T15:59:41-08:00
2008-11-04T13:59:41-08:00
<is_at_capacity>false</is_at_capacity>

2 2008-11-04T13:59:41-08:00 2008-12-05T17:59:41-08:00 4 5 201 2008-12-05T15:59:41-08:00 2008-11-04T13:59:41-08:00 false

When I invoke the method, via http://localhost:3000/conferences/1.json,
I get the following undesired generated json output. Basically the
builder and block that acts on to_xml is ignored or defunct.
{“name”: “Ruby Live”, “updated_at”: “2008/11/04 13:59:41 -0800”, “id”:
1, “created_at”: “2008/11/04 13:59:41 -0800”}

I need to support both xml and json formats while returning the same
data. Can someone please tell me what if there is a plugin or newer
version of Rails that will add this same support for to_json that
to_xml supports?Our application needs to support both xml and json
formats while returning the same data. In some cases, we need to
return custom XML that spans several objects and associations. I’ve
been able to write custom to_xml methods that use the builder and
block functionality. When trying the same thing with the to_json
method, I failed to get the same result. Can someone please tell me
if I’ve done something wrong with the code below? Is there is a
plugin or newer version of Rails that will add the
same support for to_json that to_xml supports?

Here is the relevant code

class Conference < ActiveRecord::Base
has_many :courses, :dependent => :destroy
end

class Course < ActiveRecord::Base
belongs_to :conference
has_many :sessions, :dependent => :destroy
has_one :manual

        # just a place holder method so we can serialize it

def pre_requisite
“An open mind”
end
end

class Session < ActiveRecord::Base
belongs_to :courses
has_one :presentation, :dependent=>:destroy

        # just a place holder method so we can serialize it

def maximum_capacity_reached?
false;
end
end

class Presentation < ActiveRecord::Base
belongs_to :session
belongs_to :instructor
end

class Manual < ActiveRecord::Base
belongs_to :course
end

class Instructor < ActiveRecord::Base
end

Now let’s suppose I have a controller that will return the full detail
of a conference and needs all of the related data and will also
serialize some custom methods.
class ConferencesController < ApplicationController

GET /conferences/:id

def show
conference_id = params[:id]

respond_to do |format|
  format.html # unsupported
  format.json {
    render(:json=>Conference.full_json(conference_id))
  }
  format.xml {
    render(:xml=>Conference.full_xml(conference_id))
  }
end

end
end

So I’ve extended the conference class so that it can build this nested
xml along with the result of selective methods on various classes.
class Conference < ActiveRecord::Base
has_many :courses, :dependent => :destroy

def slogan
“#{name}: Be here or be in the dark!”
end

def self.full_xml(conference_id)
# ensure we’ve loaded the full structure in the most efficient
manner
conference = Conference.find(conference_id, :include=>{:courses =>
[:manual, {:sessions=>:presentation}]})

# extract detailed hierarchical xml
conference.to_xml do |xml|
  xml.slogan conference.slogan # output the banner

  #iterate courses and any custom methods
  xml.courses{
    conference.courses.each do |course|
      course.to_xml(:builder=>xml, :skip_instruct => true) do |

xml_course|
xml_course.sessions{
#iterate sessions and any custom methods
course.sessions.each do |session|
session.to_xml(:builder=>xml_course, :skip_instruct =>
true)
do |xml_course_session|
xml_course_session.is_at_capacity
session.maximum_capacity_reached?
end
end
}
end
end
}
end
end

def self.full_json(conference_id)
# ensure we’ve loaded the full structure in the most efficient
manner
conference = Conference.find(conference_id, :include=>{:courses =>
[:manual, {:sessions=>:presentation}]})

debugger()

# extract detailed hierarchical xml
conference.to_json do |json|
  json.slogan conference.slogan # output the banner

  #iterate courses and any custom methods
  json.courses{
    conference.courses.each do |course|
      course.to_json(:builder=>json, :skip_instruct => true) do |

json_course|
json_course.sessions{
#iterate sessions and any custom methods
course.sessions.each do |session|
session.to_json(:builder=>json_course, :skip_instruct =>
true)
do |json_course_session|
json_course_session.is_at_capacity
session.maximum_capacity_reached?
end
end
}
end
end
}
end
end
end

When I invoke the method, via http://localhost:3000/conferences/1.xml,
I get the desired generated XML output:

2008-11-04T13:59:41-08:00
1
Ruby Live
2008-11-04T13:59:41-08:00
Ruby Live: Be here or be in the dark!


1
Action Controller: In Depth
2008-11-04T13:59:41-08:00
1
2008-11-04T13:59:41-08:00


1
2008-11-04T13:59:41-08:00
2008-12-04T15:59:41-08:00
1
4
101
2008-12-04T13:59:41-08:00
2008-11-04T13:59:41-08:00
<is_at_capacity>false</is_at_capacity>


1
2008-11-04T13:59:41-08:00
2008-12-05T15:59:41-08:00
2
4
101
2008-12-05T13:59:41-08:00
2008-11-04T13:59:41-08:00
<is_at_capacity>false</is_at_capacity>



+

1
Active Record: In Depth
2008-11-04T13:59:41-08:00
2
2008-11-04T13:59:41-08:00


2
2008-11-04T13:59:41-08:00
2008-12-04T17:59:41-08:00
3
5
201
2008-12-04T15:59:41-08:00
2008-11-04T13:59:41-08:00
<is_at_capacity>false</is_at_capacity>

2 2008-11-04T13:59:41-08:00 2008-12-05T17:59:41-08:00 4 5 201 2008-12-05T15:59:41-08:00 2008-11-04T13:59:41-08:00 false

When I invoke the method, via http://localhost:3000/conferences/1.json,
I get the following undesired generated json output. Basically the
builder and block that acts on to_xml is ignored or defunct.
{“name”: “Ruby Live”, “updated_at”: “2008/11/04 13:59:41 -0800”, “id”:
1, “created_at”: “2008/11/04 13:59:41 -0800”}

I need to support both xml and json formats while returning the same
data. Can someone please tell me what if there is a plugin or newer
version of Rails that will add this same support for to_json that
to_xml supports?


#2

On 5 Nov 2008, at 02:49, RubyNewbie wrote:

to a block
and provide the json builder? Can someone please tell me if I’ve done
something wrong with the code below? Is there is a plugin or newer
version of Rails that will add the same support for to_json that
to_xml supports?

I don’t believe there is a json builder - it’s just not how the json
stuff in rails works. basically there’s an obvious implementation of
to_json for hashes and arrays, everything else just hangs off that (so
to_json on an activerecord object basically takes the hash of
attributes (module except/only etc… options) and calls to_json on it)

Fred