Get values from JSON url whit Ruby on Rails

Question

I need GET value from hash of hashes of Ruby on Rails

@result = {
  "destination_addresses" => [
    "Matucana 775, Santiago Centro, Región  Metropolitana de Santiago de Chile, Chile"
  ],
  "origin_addresses" => [
    "San Pablo 6134, Lo Prado, Región Metropolitana de Santiago de Chile, Chile"
  ],
  "rows" => [
    {
      "elements" => [
        {
          "distance" => { 
            "text" => "10,0 km",
            "value" => 9957
          },
          "duration" => {
            "text" => "15 min",
            "value" => 903
          },
          "status"=>"OK"
         }
       ]
     }
   ],
 "status"=>"OK"
}

@duration = @result["rows"]["elements"]["distance"]["value"]
@distance = @result["rows"]["elements"]["duration"]["value"]

This results in:

ERROR:
can't convert String into Integer

twonegatives · Accepted Answer · 2014-06-12 18:06:50Z

1

The problem is that rows and elements are arrays, not hashes as you expect in your query. This one should work fine:

@duration = @result["rows"][0]["elements"][0]["duration"]["value"]
@distance = @result["rows"][0]["elements"][0]["distance"]["value"]

In a nutshell, this kind of problems can be simply debugged with puts for each single [] operation. Just go on outputting values to the screen till you get any error, which would tell you which part of your hash should be explored more carefully.

puts "#{@result['rows']}"
puts "#{@result['rows'][0]}"
puts "#{@result['rows'][0]['elements']}"
# etc, till you get an error instead of the value

Assuming you are working with Google maps API, you will probably end up with some queries returning data in a different format. Sometimes you can get @result object without rows or may be a row entry without elements. Here is the way to handle this:

get_value = lambda do |api_response, inner_key|
  result = api_response['rows']
  [0, 'elements', 0, inner_key, 'value'].each do |key|
    return nil unless result
    result = result[key]
  end
  result
end

@duration = get_value.call(@result, 'duration')
@distance = get_value.call(@result, 'distance')

In case any of your @duration or @distance variables is nil at the end of this block, you can be sure that Google maps API did not parse your query correctly.

edited Jun 12, 2014 at 18:06

answered Jun 11, 2014 at 23:22

twonegatives

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3 Comments

user3686763 Over a year ago

undefined method `[]' for nil:NilClass

twonegatives Over a year ago

That is weird. Take a look at this pastie, it contains the hash and the @duration and @distance queries returning the result. Are you sure the @result hash is completely the same as in your question and you copy-pasted the queries from the answer correctly? I have also updated my answer with an idea of how to find a failing step of the operation.

user3686763 Over a year ago

stackoverflow.com/questions/24177311/… Here is my code for a webpage.

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