opening json string to easily read and write to in ruby - json

Question

I have a json file. I am using it to store information, and as such it is constantly going to be both read and written.
I am completely new to ruby and oop in general, so I am sure I am going about this in a crazy way.
class Load
def initialize(save_name)
puts "loading " + save_name
#data = JSON.parse(IO.read( $user_library + save_name ))
#subject = #data["subject"]
#id = #data["id"]
#save_name = #data["save_name"]
#listA = #data["listA"] # is an array containing dictionaries
#listB = #data["listB"] # is an array containing dictionaries
end
attr_reader :data, :subject, :id, :save_name, :listA, :listB
end
example = Load.new("test.json")
puts example.id
=> 937489327389749
So I can now easily read the json file, but how could I write back to the file - refering to example? say I wanted to change the id example.id.change(7129371289)... or add dictionaries to lists A and B... Is this possible?

Answer 1

The simplest way to go to/from JSON is to just use the JSON library to transform your data as appropriate:
json = my_object.to_json — method on the specific object to create a JSON string.
json = JSON.generate(my_object) — create JSON string from object.
JSON.dump(my_object, someIO) — create a JSON string and write to a file.
my_object = JSON.parse(json) — create a Ruby object from a JSON string.
my_object = JSON.load(someIO) — create a Ruby object from a file.
Taken from this answer to another of your questions.
However, you could wrap this in a class if you wanted:
class JSONHash
require 'json'
def self.from(file)
self.new.load(file)
end
def initialize(h={})
#h=h
end
# Save this to disk, optionally specifying a new location
def save(file=nil)
#file = file if file
File.open(#file,'w'){ |f| JSON.dump(#h, f) }
self
end
# Discard all changes to the hash and replace with the information on disk
def reload(file=nil)
#file = file if file
#h = JSON.parse(IO.read(#file))
self
end
# Let our internal hash handle most methods, returning what it likes
def method_missing(*a,&b)
#h.send(*a,&b)
end
# But these methods normally return a Hash, so we re-wrap them in our class
%w[ invert merge select ].each do |m|
class_eval <<-ENDMETHOD
def #{m}(*a,&b)
self.class.new #h.send(#{m.inspect},*a,&b)
end
ENDMETHOD
end
def to_json
#h.to_json
end
end
The above behaves just like a hash, but you can use foo = JSONHash.from("foo.json") to load from disk, modify that hash as you would normally, and then just foo.save when you want to save out to disk.
Or, if you don't have a file on disk to begin with:
foo = JSONHash.new a:42, b:17, c:"whatever initial values you want"
foo.save 'foo.json'
# keep modifying foo
foo[:bar] = 52
f.save # saves to the last saved location