how to fetch values in hash array ruby

Question

i have written small ruby code to get publish stats, code is following

begin
  response = conn.get("api/queues")
  statistics = JSON.parse(response.body)

  statistics.each do |qDetails|
    payload = "#{qDetails["name"]}"
    if payload != "aliveness-test"
      puts "#{qDetails["message_stats"]["publish"]}"          
    end             
  end      
rescue Faraday::Error::ConnectionFailed => e
  puts "Connection failed"
end

but i get this error in return

undefined method `[]' for nil:NilClass (NoMethodError)

message_stats json would be like this

{"deliver_get_details"=>{"rate"=>0.0}, "deliver_get"=>1357, "ack_details"=>{"rate"=>0.0}, "ack"=>1357, "redeliver_details"=>{"rate"=>0.0}, "redeliver"=>0, "deliver_no_ack_details"=>{"rate"=>0.0}, "deliver_no_ack"=>0, "deliver_details"=>{"rate"=>0.0}, "deliver"=>1357, "get_no_ack_details"=>{"rate"=>0.0}, "get_no_ack"=>0, "get_details"=>{"rate"=>0.0}, "get"=>0, "publish_details"=>{"rate"=>0.0}, "publish"=>1400}

what's the issue?

when i change the code to this puts "#{qDetails["message_stats"]}" it works but whole json would print — frodo
– frodo, Commented Mar 12, 2018 at 10:52
On what line do you get the error? Are you sure "message_stats" is always filled in, because that would explain immediately. — nathanvda
– nathanvda, Commented Mar 12, 2018 at 10:58
@nathanvda i want to get publish data so when i add ["publish"] i get that error. — frodo
– frodo, Commented Mar 12, 2018 at 11:02

Jaffa · Accepted Answer · 2018-03-12 11:24:13Z

2

For ruby > 2.3, you can use dig:

qDetails.dig("message_stats", "publish")

This will safely access qDetails["message_stats"]["publish"]

The error you're getting is probably because qDetails["message_stats"] is nil, so calling [] on it doesn't work

answered Mar 12, 2018 at 11:24

Jaffa

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3 Comments

Jaffa Over a year ago

@frodo why unaccept the answer then, and even more to accept a poor rephrasing of this one?

Pac0 Over a year ago

@Geoffroy it seems not fair indeed. I suggest you to flag the other copied answer, and explain precisely what happened.

Pac0 Over a year ago

(btw, the same user posted another copy-paste answer on a question of mine)

Ashik Salman · Accepted Answer · 2018-03-13 06:55:15Z

0

You can use ruby-fetch method to get the data from hash where you are unsure about existence of a key. You can also set default value to return unlike dig returns nil if value not found

qDetails["message_stats"].fetch("publish", "default_value")

Another way would be like by using safe navigation operator (&):

qDetails["message_stats"]&.[]('publish') # Return nil if not found

answered Mar 13, 2018 at 6:55

Ashik Salman

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