CODEWITHSUNDEEP
ruby-on-railsruby
jiveTurkey
jiveTurkey

Reputation: 729

Merging two ruby objects

Question: Is there a concise way in Ruby (and/or Rails) to merge two objects together?

Specifically, I'm trying to figure out something akin to jQuery's $.extend() method, whereas the first object you pass in will have its properties overridden by the second object.

I'm working with a tableless model in Rails 3.2+. When a form submission occurs, the parameters from the submission are used to dynamically populate a User object. That user object is persisted between page requests using Ruby's PStore class, marshalling objects to flat files which can be easily retrieved in the future.

Relevant code:

module Itc
  class User
    include ActiveModel::Validations
    include ActiveModel::Conversion
    include ActionView::Helpers
    extend ActiveModel::Naming

    def set_properties( properties = {} )
      properties.each { |k, v|
        class_eval("attr_reader :#{k.to_sym}")
        self.instance_variable_set("@#{k}", v)
      } unless properties.nil?
    end
  end
end

Creation of a user object occurs like this:

user = Itc.User.new( params[:user] )
user.save()

The save() method above is not ActiveRecord's save method, but a method I wrote to do persistence via PStore.

If I have a user object loaded, and I have a form submission, I'd like to do something like this:

merged = existingUserObject.merge(User.new(params[:user])

and have the outcome of merged be a user object, with only properties that were changed in the form submission be updated.

If anyone has any ideas about a better way to do this in general, I'm all ears.

Upvotes: 12

Views: 35537

Answers (3)

Sumit Maheshwari
Sumit Maheshwari

Reputation: 59

This is how I achieved similar thing with 1 of my model

  # merge other_config.attrs into self.attrs, only for nil attrs
  def merge!(other_object)
    return if other_object.nil? || other_object.class != self.class
    self.assign_attributes(self.attributes.slice ('id').merge(other_object.attributes.slice!('id')){|key, oldval, newval|
      oldval.nil? ? newval: oldval
    })
  end

Upvotes: 0

JGrubb
JGrubb

Reputation: 889

Is Hash#merge not what you're looking for? http://www.ruby-doc.org/core-1.9.3/Hash.html#method-i-merge. Seems like you could just go 

merged = existingUserObject.merge(params[:user])

I don't think you need to create an entirely new User object since presumably that's what existingUserObject is and you just want to overwrite some properties.

Upvotes: 19

the Tin Man
the Tin Man

Reputation: 160551

Do it by piggybacking on hash's behaviors. Create a class that takes a hash for the parameter of the new() method, and then a to_h method that takes an object and generates a hash from the current state of the instance: 

class Foo
  def initialize(params={})
    @a = params[:a]
    @b = params[:b]
  end

  def to_h
    {
      a: @a,
      b: @b
    }
  end
end

instance_a = Foo.new(a: 1, b:2)
instance_b = Foo.new(a: 1, b:3)

instance_c = Foo.new(instance_a.to_h.merge(instance_b.to_h))

Dumping it into IRB:

irb(main):001:0> class Foo
irb(main):002:1>   def initialize(params={})
irb(main):003:2>     @a = params[:a]
irb(main):004:2>     @b = params[:b]
irb(main):005:2>   end
irb(main):006:1> 
irb(main):007:1*   def to_h
irb(main):008:2>     {
irb(main):009:3*       a: @a,
irb(main):010:3*       b: @b
irb(main):011:3>     }
irb(main):012:2>   end
irb(main):013:1> end
nil
irb(main):014:0> 
irb(main):015:0* instance_a = Foo.new(a: 1, b:2)
#<Foo:0x1009cfd00
    @a = 1,
    @b = 2
>
irb(main):016:0> instance_b = Foo.new(a: 1, b:3)
#<Foo:0x1009ead08
    @a = 1,
    @b = 3
>
irb(main):017:0> 
irb(main):018:0* instance_c = Foo.new(instance_a.to_h.merge(instance_b.to_h))
#<Foo:0x100a06c60
    @a = 1,
    @b = 3
>

Upvotes: 4

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