Ruby objects and JSON serialization without Rails

Question

I m trying to understand the JSON serialization landscape in Ruby  I m new to Ruby   Is there any good JSON serialization options if you are not working with Rails   That seems to be where this answer goes  to Rails  How to convert a Ruby object to JSON  The json gem seems to make it look like you have to write your own to json method  I haven t been able to get to json to work with arrays and hashes  documentation says it works with these  Is there a reason the json gem doesn t just reflect over the object and use a default serialization strategy  Isn t this how to yaml works  guessing here

User · Answer

If rendering performance is critical  you might also want to look at yajl-ruby  which is a binding to the C yajl library   The serialization API for that one looks like   require  yajl  Yajl  Encoder encode   foo    gt   bar       gt      foo     bar

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For the JSON library to be available  you may have to install libjson-ruby from your package manager   To use the  json  library   require  json    To convert an object to JSON  these 3 ways are equivalent    JSON dump object  returns a JSON string JSON generate object  returns a JSON string object to json  returns a JSON string   To convert JSON text to an object  these 2 ways are equivalent    JSON load string  returns an object JSON parse string  returns an object   It will be a bit more difficult for objects from your own classes  For the following class  to json will produce something like      lt A 0xb76e5728 gt       class A     def initialize a  1 2 3   b  hello           a   a          b   b     end end   This probably isn t desirable  To effectively serialise your object as JSON  you should create your own to json method  To go with this  a from json class method would be useful  You could extend your class like so   class A     def to json           a    gt   a   b    gt   b  to json     end     def self from json string         data   JSON load string         self new data  a    data  b       end end   You could automate this by inheriting from a  JSONable  class   class JSONable     def to json         hash              self instance variables each do  var              hash var    self instance variable get var         end         hash to json     end     def from json  string         JSON load string  each do  var  val              self instance variable set var  val         end     end end   Then you can use object to json to serialise to JSON and object from json  string to copy the saved state that was saved as the JSON string to the object

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If you re using 1 9 2 or above  you can convert hashes and arrays to nested JSON objects just using to json     a   1 2 3   b  4  to json   In Rails  you can call to json on Active Record objects  You can pass  include and  only parameters to control the output    user to json only    name   email    You can also call to json on AR relations  like so   User order  id DESC   limit 10  to json   You don t need to import anything and it all works exactly as you d hope

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To get the build in classes  like Array and Hash  to support as json and to json  you need to require  json add core   see the readme for details

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Jbuilder is a gem built by rails community  But it works well in non-rails environments and have a cool set of features     suppose we have a sample object as below sampleObj name    gt  foo sampleObj last name    gt  bar    using jbuilder we can convert it to json  Jbuilder encode do  json    json name sampleObj name   json last name sampleObj last name end    gt       name     gt    foo       last name     gt    bar

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require  json    foo    gt   bar   to json     gt      foo     bar

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Actually  there is a gem called Jsonable  https   github com treeder jsonable  It s pretty sweet

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I used to virtus  Really powerful tool  allows to create a dynamic Ruby structure structure based on your specified classes  Easy DSL  possible to create objects from ruby hashes  there is strict mode  Check it out

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Since I searched a lot myself to serialize a Ruby Object to json    require  json   class User   attr accessor  name   age    def initialize name  age       name   name      age   age   end    def as json options                 name   name        age   age         end    def to json  options      as json  options  to json  options    end end  user   User new  Foo Bar   42  puts user to json    gt    name   Foo Bar   age  42

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Check out Oj  There are gotchas when it comes to converting any old object to JSON  but Oj can do it   require  oj   class A     def initialize a  1 2 3   b  hello           a   a          b   b     end end  a   A new puts Oj  dump a   indent   gt  2   This outputs         o   A      a        1      2      3        b   hello      Note that  o is used to designate the object s class  and is there to aid deserialization  To omit  o  use  compat mode   puts Oj  dump a   indent   gt  2   mode   gt   compat   Output        a        1      2      3         b   hello

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What version of Ruby are you using  ruby -v will tell you    If it s 1 9 2  JSON is included in the standard library    If you re on 1 8 something then do gem install json and it ll install  Then  in your code do   require  rubygems  require  json    Then append to json to an object and you re good to go   asdf     a    gt   b      gt    a   gt  b   asdf to json    gt     a   b

[ruby] Ruby objects and JSON serialization (without Rails)

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