Building JSON Object from array with specific keys and values in Ruby 2.0

Question

I'm getting a bit stuck building a json object from a parent and child relationship. I have a Parent model with many Children.

I'm trying to create a JSON object as so:

{ parent_1.name: { parent_1.child.age, parent_1.child.height}, parent_1.name: { child_2.age, child_2.height}, parent_2.name: ...... }

This SO question has helped a lot but I can't figure it out completely.

I have tried this:

Parent.all.inject({}) { |hsh, p| hsh[p.name] = { p.name => p.children.inject({}) { |h,v| h[v] = {age: v.age, height: v.height}} }}

Which is really close (but horrible looking). However I only get one parent's children - I need all the parents with the children. I only need the height and age of the children. The output was like this (I have excluded the conversion to json):

{"BarryWhite"=>{:age=>"12", :height=>"45cm"}}

It should look something like this:

{"BarryWhite"=>{:age=>"12", :height=>"45cm"}, {:age => "34", :height => "108cm"}, "AndyMurray"=>{:age=>"14", :height=>"125cm"}}

How can I get this to output the correctly formatted json.

Nikita Chernov · Accepted Answer · 2013-07-12 14:58:47Z

1

First of all the JSON format you require is a bit incorrect.

I assume children should be an array of hashes, like:

{
  'BarryWhite' => [
    { :age => '12', :height => '45cm'  },
    { :age => '34', :height => '108cm' }
  ]
  'AndyMurray' => [
    { :age => '14', :height => '125cm' }
  ]
}

For this you don't need an inner #inject, as you don't need a hash, but an array.

Also you are using #inject a bit incorrectly with hashes. #inject builds up a hash by passing through the loop the last executed statement. Your last executed statement is an assignment which returns only the current value of a variable "p". You should return the whole "hsh" all the time.

Here is the working solution:

Parent.all.inject({}) do |hsh, p|
  hsh[p.name] = p.children.map { |c| {age: c.age, height: c.height} }
  hsh
end

answered Jul 12, 2013 at 14:58

Nikita Chernov

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1 Comment

simonmorley Over a year ago

Good point about the formatting. I'd forgotten to put that in.. Thanks, all sorted. S

Kevin · Accepted Answer · 2014-03-17 23:56:29Z

0

Here's how I do it:

1) Each model has a to_json method

2) When rendering, render json: @items.collect(&:to_json)

I'm not sure why it doesn't automatically call to_json on child objects when array.to_json is called.

answered Mar 17, 2014 at 23:56

Kevin

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