Strong parameters with json array

Give this a try:

2.3.1 :034 > JSON.parse(params.permit(:comments)[:comments])
Unpermitted parameters: format, id
 => [{"comment"=>"ndjsnjakldnfljkasdbfhjae", "date"=>"2017-07-20 17:14:38"}]  

params.permit(:comments) returns the params hash with only the "comments" k,v pair (dropping the unpermitted parameters, format and id):

2.3.1 :035 > params.permit(:comments)
Unpermitted parameters: format, id
 => {"comments"=>"[{\"comment\":\"ndjsnjakldnfljkasdbfhjae\",\"date\":\"2017-07-20 17:14:38\"}]"} 

params.permit(:comments)[:comments] selects the value for the :comments key from the hash:

2.3.1 :036 > params.permit(:comments)[:comments]
Unpermitted parameters: format, id
 => "[{\"comment\":\"ndjsnjakldnfljkasdbfhjae\",\"date\":\"2017-07-20 17:14:38\"}]" 

JSON.parse(params.permit(:comments)[:comments]) converts the string to a proper ruby array.

From there, you can do as you like with the ruby array object.

If you want both :comments and :id, then just:

params.permit(:comments, :id)
Unpermitted parameter: format
 => {"comments"=>"[{\"comment\":\"ndjsnjakldnfljkasdbfhjae\",\"date\":\"2017-07-20 17:14:38\"}]", "id"=>"13534543543"} 

To get the individual parts:

2.3.1 :038 > params.permit(:comments, :id)[:comments]
Unpermitted parameter: format
 => "[{\"comment\":\"ndjsnjakldnfljkasdbfhjae\",\"date\":\"2017-07-20 17:14:38\"}]" 

and:

2.3.1 :039 > params.permit(:comments, :id)[:id]
Unpermitted parameter: format
 => "13534543543" 

You probably want to wrap it in something like:

def clean_params
  @clean_params ||= params.permit(:comments, :id)
end

So you can do clean_params[:comments] and clean_params[:id].