Issues creating a model instance - TypeMismatch error in Ruby on Rails -

i'm getting error , don't understand why. have form passes control input create model instance with.

here form:

=form_for :message, :url => {:action => 'create', :controller => 'messages'} |f|     =f.text_area :body, :placeholder => 'enter message.', :size => '40x5'     =f.hidden_field :subject, value: "re:#{@message.subject}"     =f.hidden_field :parent, value: @message.id     =f.hidden_field :receiver, value: @message.sender     =f.submit 'reply' 

here controller:

def create     user = user.find_by_username(params[:message][:receiver])#remove receiver , give varibale -rg 4/29     if user ||= user.find_by_id(params[:message][:receiver]).username#valid entry -rg 4/29         params[:message].delete('receiver')         params[:message][:status] = 'unread'#set status -rg 4/29         params[:message][:sender] = @current_user#set sender -rg 4/29         # raise params.inspect 13 =>   @message = message.create!(params[:message])#create message! -rg 4/29         if parent = params[:message][:parent]#checks if reply message -rg 4/29             message.find_by_id(parent).update_attributes(:child => @message)#updates parent message have message child -rg 4/29         end         @message.received<<user#adds receiver database         flash[:notice] = "message sent."         redirect_to messages_path     else         flash[:warning] = "there no user username."         redirect_to messages_path     end end 

and message model:

class message < activerecord::base    attr_accessible :body, :subject, :status, :sender, :receiver,:parent, :child    belongs_to :sent, :class_name => 'user'    has_and_belongs_to_many :received, :class_name => 'user'    belongs_to :parent, :class_name => 'message'    has_one :child, :class_name => 'message' end 

the error getting, including trace:

 activerecord::associationtypemismatch in messagescontroller#create   message(#41016000) expected, got string(#17696120)   rails.root: /home/renee/classes/se/brainstormy  application trace | framework trace | full trace   app/controllers/messages_controller.rb:13:in `create' 

here params being passed:

{"utf8"=>"✓",  "authenticity_token"=>"ylytxntjludk15dm554vpjom7hlqcc2d+hgmkuljcee=",  "message"=>{"body"=>"j",  "subject"=>"re:j",  "parent"=>"1",  "status"=>"unread",  "sender"=>2},  "commit"=>"reply"} 

it's interesting because have second form uses same controller works perfectly. seems field have, :parent culprit. want don't want pass message. want pas integer id. it's getting passed string. can me fix this?

this because passing in string (f.hidden_field :parent, value: @message.id) parent association method requires message object. want set foreign_key field parent association message id.

if foreign_key parent_id, hidden field should this:

f.hidden_field :parent_id, value: @message.id 

you'll have check if making :parent accessible same making :parent_id accessible otherwise won't set.