Collecting hashes into OpenStruct creates “table” entry

Question

Why this (evaluated in Rails console)

[{:a => :b}].collect {|x| OpenStruct.new(x)}.to_json

adds a \"table\" record in there?

Answer 1

With ruby 2.1.2 you can use the following to get JSON without the table root element:

[{:a => :b}].collect {|x| OpenStruct.new(x).to_h}.to_json
 => "[{\"a\":\"b\"}]"

Answer 2

I get around the problem by subclassing OpenStruct like so:

class DataStruct < OpenStruct
  def as_json(*args)
    super.as_json['table']
  end
end

then you can easily convert to JSON like so:

o = DataStruct.new(a:1, b:DataStruct.new(c:3))
o.to_json
# => "{\"a\":1,\"b\":{\"c\":3}}"

Neat huh? So in answer to your question, you'd write this instead:

[{:a => :b}].collect {|x| DataStruct.new(x)}.to_json

giving you:

=> "[{\"a\":\"b\"}]"

Answer 3

openstruct_array.map(&:to_h).as_json

Answer 4

I found the other responses to be a tad confusing having landed here to just figure out how to turn my OpenStruct into a Hash or JSON. To clarify, you can just call marshal_dump on your OpenStruct.

$ OpenStruct.new(hello: :world).to_json
=> "{\"table\":{\"hello\":\"world\"}}"

$ OpenStruct.new(hello: :world).marshal_dump
=> {:hello=>:world}

$ OpenStruct.new(hello: :world).marshal_dump.to_json
=> "{\"hello\":\"world\"}"

I personally would be hesitant to monkey-patch OpenStruct unless you're doing it on a subclass, as it may have unintended consequences.

Answer 5

Because @table is a instance variable of OpenStruct and Object#as_json returns Hash of instance variables.

In my project, I implemented OpenStruct#as_json to override the behaviour.

require "ostruct"
class OpenStruct
  def as_json(options = nil)
    @table.as_json(options)
  end
end

Answer 6

Use marshal_dump, although this somewhat defeats the purpose of converting it to an OpenStruct beforehand:

[{:a => :b}].collect {|x| OpenStruct.new(x).marshal_dump }.to_json
=> "[{\"a\":\"b\"}]"

The shorter way would be:

[{:a => :b}].to_json
"[{\"a\":\"b\"}]"

Alternatively you could moneky patch OpenStruct#as_json as shown in hiroshi's answer:

require "ostruct"
class OpenStruct
  def as_json(options = nil)
    @table.as_json(options)
  end
end