How can i create JSON array of JSON objects in ruby from a loop

Question

I am trying to loop through some video objects and i am trying to build a JSON array that looks like this:

[{"event_name":"video_completed","object_id":123456789}]

I created a method to do this:

def self.getEngagementRules(videos)

    rules = []

    videos.each do |video|

        rule = {
            event_name: "video_completed",
            object_id: video.image_hash.to_i
        }

        rules << rule.to_json
    end

    rules
end

I am creating hashes and then turning them into JSON and appending it to my array rules but when i run:

puts rules

i get {"event_name":"video_completed","object_id":123456789}

instead of [{"event_name":"video_completed","object_id":123456789}]

What is the correct way of doing this so i can loop through multiple videos and get my desired result.

It should be able to handle multiple videos and output:

[{"event_name":"video_completed","object_id":123456789}, {"event_name":"video_completed","object_id":123456789}]

Your code works fine, aren't you printing rule instead of rules by mistake? Also, each element in your array will be a string representing a JSON ["{\"event_name\":\"video_completed\",\"object_id\":1234}"] — EmmanuelB
– EmmanuelB, Commented Nov 16, 2018 at 14:52

max · Accepted Answer · 2022-05-06 07:38:07Z

5

You want to first compose a ruby array and then convert it to JSON:

rules = videos.map do |video|
  {
    event_name: "video_completed",
    object_id: video.image_hash.to_i
   }
end
rules.to_json

.each should only be used when you are only concerned with the side effects of the loop and not the return value.

Otherwise you should be using .map, .inject, .each_with_object etc which signify to other programmers that you care about the return value.

edited May 6, 2022 at 7:38

answered Nov 16, 2018 at 14:54

max

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3 Comments

ricks Over a year ago

What do you mean by 'side effects of the loop'?

max Over a year ago

For example in ERB templates you use .each since you are outputting to a string buffer and the return value is not used.

ricks Over a year ago

Thanks! I might need to go through my project and see where else i can use map instead of each haha

user5085788 · Accepted Answer · 2018-11-16 14:54:01Z

1

Your code works right, you have an array but puts prints each element of the array in a separate line

puts [1, 2, 3]

1
2
3

answered Nov 16, 2018 at 14:54

user5085788

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