ruby on rails - how to permit an array with strong parameters -

i have functioning rails 3 app uses has_many :through associations not, remake rails 4 app, letting me save ids associated model in rails 4 version.

these 3 relevant models same 2 versions.

categorization.rb

class categorization < activerecord::base    belongs_to :question   belongs_to :category end 

question.rb

has_many :categorizations has_many :categories, through: :categorizations 

category.rb

has_many :categorizations has_many :questions, through: :categorizations 

in both apps, category ids getting passed create action this

  "question"=>{"question_content"=>"how spell car?", "question_details"=>"blah ", "category_ids"=>["", "2"], 

in rails 3 app, when create new question, inserts questions table , categorizations table

 sql (82.1ms)  insert "questions" ("accepted_answer_id", "city", "created_at", "details", "province", "province_id", "question", "updated_at", "user_id") values (?, ?, ?, ?, ?, ?, ?, ?, ?)  [["accepted_answer_id", nil], ["city", "dd"], ["created_at", tue, 14 may 2013 17:10:25 utc +00:00], ["details", "greyound?"], ["province", nil], ["province_id", 2], ["question", "whos' biggest dog in world"], ["updated_at", tue, 14 may 2013 17:10:25 utc +00:00], ["user_id", 53]]   sql (0.4ms)  insert "categorizations" ("category_id", "created_at", "question_id", "updated_at") values (?, ?, ?, ?)  [["category_id", 2], ["created_at", tue, 14 may 2013 17:10:25 utc +00:00], ["question_id", 66], ["updated_at", tue, 14 may 2013 17:10:25 utc +00:00]] 

in rails 4 app, after processes parameters in questioncontroller#create, i'm getting error in server logs

unpermitted parameters: category_ids 

and question getting inserted questions table

 (0.2ms)  begin   sql (67.6ms)  insert "questions" ("city", "created_at", "province_id", "question_content", "question_details", "updated_at", "user_id") values ($1, $2, $3, $4, $5, $6, $7) returning "id"  [["city", "dd"], ["created_at", tue, 14 may 2013 17:17:53 utc +00:00], ["province_id", 3], ["question_content", "how's car?"], ["question_details", "is runnign"], ["updated_at", tue, 14 may 2013 17:17:53 utc +00:00], ["user_id", 12]]    (31.9ms)  commit 

although not storing category_ids on questions model, set category_ids permitted parameter in questions_controller

   def question_params        params.require(:question).permit(:question_details, :question_content, :user_id, :accepted_answer_id, :province_id, :city, :category_ids)     end 

can explain how i'm supposed save category_ids? note, there no create action in categories_controller.rb of either app.

these 3 tables same in both apps

 create_table "questions", force: true |t|     t.text     "question_details"     t.string   "question_content"     t.integer  "user_id"     t.integer  "accepted_answer_id"     t.datetime "created_at"     t.datetime "updated_at"     t.integer  "province_id"     t.string   "city"   end   create_table "categories", force: true |t|     t.string   "name"     t.datetime "created_at"     t.datetime "updated_at"   end    create_table "categorizations", force: true |t|     t.integer  "category_id"     t.integer  "question_id"     t.datetime "created_at"     t.datetime "updated_at"   end 

update

this create action rails 3 app

  def create       @question = question.new(params[:question])       respond_to |format|       if @question.save         format.html { redirect_to @question, notice: 'question created.' }         format.json { render json: @question, status: :created, location: @question }       else         format.html { render action: "new" }         format.json { render json: @question.errors, status: :unprocessable_entity }       end     end end 

this create action rails 4 app

   def create       @question = question.new(question_params)         respond_to |format|       if @question.save         format.html { redirect_to @question, notice: 'question created.' }         format.json { render json: @question, status: :created, location: @question }       else         format.html { render action: "new" }         format.json { render json: @question.errors, status: :unprocessable_entity }       end     end     end 

this question_params method

 private     def question_params        params.require(:question).permit(:question_details, :question_content, :user_id, :accepted_answer_id, :province_id, :city, :category_ids)     end 

this https://github.com/rails/strong_parameters seems relevant section of docs:

the permitted scalar types string, symbol, nilclass, numeric, trueclass, falseclass, date, time, datetime, stringio, io, actiondispatch::http::uploadedfile , rack::test::uploadedfile.

to declare value in params must array of permitted scalar values map key empty array:

params.permit(:id => []) 

in app, category_ids passed create action in array

"category_ids"=>["", "2"], 

therefore, when declaring strong parameters, explicitly set category_ids array

params.require(:question).permit(:question_details, :question_content, :user_id, :accepted_answer_id, :province_id, :city, :category_ids => []) 

works now!