Converting nested hash keys from CamelCase to snake_case in Ruby - ruby

Question

I'm trying to build an API wrapper gem, and having issues with converting hash keys to a more Rubyish format from the JSON the API returns.
The JSON contains multiple layers of nesting, both Hashes and Arrays. What I want to do is to recursively convert all keys to snake_case for easier use.
Here's what I've got so far:
def convert_hash_keys(value)
return value if (not value.is_a?(Array) and not value.is_a?(Hash))
result = value.inject({}) do |new, (key, value)|
new[to_snake_case(key.to_s).to_sym] = convert_hash_keys(value)
new
end
result
end
The above calls this method to convert strings to snake_case:
def to_snake_case(string)
string.gsub(/::/, '/').
gsub(/([A-Z]+)([A-Z][a-z])/,'\1_\2').
gsub(/([a-z\d])([A-Z])/,'\1_\2').
tr("-", "_").
downcase
end
Ideally, the result would be similar to the following:
hash = {:HashKey => {:NestedHashKey => [{:Key => "value"}]}}
convert_hash_keys(hash)
# => {:hash_key => {:nested_hash_key => [{:key => "value"}]}}
I'm getting the recursion wrong, and every version of this sort of solution I've tried either doesn't convert symbols beyond the first level, or goes overboard and tries to convert the entire hash, including values.
Trying to solve all this in a helper class, rather than modifying the actual Hash and String functions, if possible.
Thank you in advance.

Answer 1

If you use Rails:
Example with hash: camelCase to snake_case:
hash = { camelCase: 'value1', changeMe: 'value2' }
hash.transform_keys { |key| key.to_s.underscore }
# => { "camel_case" => "value1", "change_me" => "value2" }
source:
http://apidock.com/rails/v4.0.2/Hash/transform_keys
For nested attributes use deep_transform_keys instead of transform_keys, example:
hash = { camelCase: 'value1', changeMe: { hereToo: { andMe: 'thanks' } } }
hash.deep_transform_keys { |key| key.to_s.underscore }
# => {"camel_case"=>"value1", "change_me"=>{"here_too"=>{"and_me"=>"thanks"}}}
source: http://apidock.com/rails/v4.2.7/Hash/deep_transform_keys

Answer 2

You need to treat Array and Hash separately. And, if you're in Rails, you can use underscore instead of your homebrew to_snake_case. First a little helper to reduce the noise:
def underscore_key(k)
k.to_s.underscore.to_sym
# Or, if you're not in Rails:
# to_snake_case(k.to_s).to_sym
end
If your Hashes will have keys that aren't Symbols or Strings then you can modify underscore_key appropriately.
If you have an Array, then you just want to recursively apply convert_hash_keys to each element of the Array; if you have a Hash, you want to fix the keys with underscore_key and apply convert_hash_keys to each of the values; if you have something else then you want to pass it through untouched:
def convert_hash_keys(value)
case value
when Array
value.map { |v| convert_hash_keys(v) }
# or `value.map(&method(:convert_hash_keys))`
when Hash
Hash[value.map { |k, v| [underscore_key(k), convert_hash_keys(v)] }]
else
value
end
end

Answer 3

I use this short form:
hash.transform_keys(&:underscore)
And, as #Shanaka Kuruwita pointed out, to deeply transform all the nested hashes:
hash.deep_transform_keys(&:underscore)

Answer 4

The accepted answer by 'mu is too short' has been converted into a gem, futurechimp's Plissken:
https://github.com/futurechimp/plissken/blob/master/lib/plissken/ext/hash/to_snake_keys.rb
This looks like it should work outside of Rails as the underscore functionality is included.

Answer 5

Use deep_transform_keys for recursive conversion.
transform_keys only convert it in high level
hash = { camelCase: 'value1', changeMe: {nestedMe: 'value2'} }
hash.transform_keys { |key| key.to_s.underscore }
# => { "camel_case" => "value1", "change_me" => {nestedMe: 'value2'} }
deep_transform_keys will go deeper and transform all nested hashes as well.
hash = { camelCase: 'value1', changeMe: {nestedMe: 'value2'} }
hash.deep_transform_keys { |key| key.to_s.underscore }
# => { "camel_case" => "value1", "change_me" => {nested_me: 'value2'} }

Answer 6

If you're using the active_support library, you can use deep_transform_keys! like so:
hash.deep_transform_keys! do |key|
k = key.to_s.snakecase rescue key
k.to_sym rescue key
end

Answer 7

This works both to camelCase and snake_case deep nested keys of an object, which is very useful for a JSON API:
def camelize_keys(object)
deep_transform_keys_in_object!(object) { |key| key.to_s.camelize(:lower) }
end
def snakecase_keys(object)
deep_transform_keys_in_object!(object) { |key| key.to_s.underscore.to_sym }
end
def deep_transform_keys_in_object!(object, &block)
case object
when Hash
object.keys.each do |key|
value = object.delete(key)
object[yield(key)] = deep_transform_keys_in_object!(value, &block)
end
object
when Array
object.map! { |e| deep_transform_keys_in_object!(e, &block) }
else
object
end
end