In Ruby on Rails is there a better way than using eval() to accses this jsonb dynamically?

Question

I've got some jsonb in a database and I want to write to an attribute dynamically, I know the path to the attribute but it could be any depth and any attribute name.

I know the path to the attribute, however the only way I've found of writing this dynamiaclly is with eval().

eval("self.some_json_column['an_array'][10]['a_different_array'][5]['color'] = 'blue'")
self.save

So I know the depth and the array index, but it could be any depth or index. I can build the string and pass it into eval()

However I know that eval() is a last case scenario and was wonderign if it's possible to build the path and write (in this case that color json attribute) dynamically without using eval()

Thanks.

Answer 1

You can reduce your way through the Hash that is returned by self.some_json_column

*path, target = ['an_array',10,'a_different_array',5,'color']
node = path.reduce(self.some_json_colum, &:[])
node[target] = 'blue' if node  

This has no error handling if any part of the path is incorrect

You could also look into dig depending on ruby version like so

node = self.some_json_column.dig(*path)
node[target] = 'blue' if node

This will return nil if any part of the path does not match

Example:

h = {
  'an_array' => [0,1,2,3,4,5,6,7,8,9,
    {'a_different_array' => [1,2,3,4,5, {'color' => 'orange'}]}
  ]
}

*path,target  = ['an_array',10,'a_different_array',5,'color']

h.dig(*path)[target] = 'blue'

h
#=> {"an_array"=>[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 
#     {"a_different_array"=>[0, 1, 2, 3, 4, 
#       {"color"=>"blue"}
#     ]}
#   ]}