Rails hashes with unknown keys and strong parameters

Question

I have a rails application that stores a serialized hash in a field called properties.

The hashes keys are unknown though, so I don\'t know of a way to

Answer 1

You can use a hash instead of a symbol and define what sub-properties are allowed. This can be seen in the source here:

case filter
when Symbol, String
  permitted_scalar_filter(params, filter)
when Hash
  hash_filter(params, filter)
end

https://github.com/rails/rails/blob/bdc73a438a97f2e0aceeb745f4a95f95514c4aa6/actionpack/lib/action_controller/metal/strong_parameters.rb#L522

e.g.

def user_params
  params.require(:person).permit(:name, :description, :age, properties: [:key, :value])
end

If you have no idea what is going to be in properties you could use .slice. Note this will accept anything nested in any of the other fields too.

e.g.

def user_params
  params.require(:person).slice(:name, :description, :age, :properties) 
end

These approaches will work on the following params:

{
  "person": {
    "name": "John",
    "description": "has custom_attributes",
    "age": 42,
    "properties": [
      {
        "key": "the key",
        "value": "the value"
      }
    ]
  }
}

I've confirmed these will work on Rails 4.2.6