undefined method `sender_id=' for nil:NilClass - ruby-on-rails

Question

currently I am creating a snapchat like application by using Rails. I get the error:
undefined method `sender_id=' for nil:NilClass
while I am trying to submit the new message form, I don't really know where I make the mistake. Moreover, I am not sure about the logic of the create action in my messages_controller, basically I just want the sender sends a message to the people in their friendlist by choosing one or more recipients at the same time(of course, the recipients must be in their friendlist, and I have already accomplished this feature). However, because I still haven't figured out how can I pass the the params recipient_id to the form(I am using simple form gem and devise gem by the way), so I hardcoded the recipient_id in my create action. So,all of suggestions/advices are welcome.
Here are my files:
messages_controller.rb:
class MessagesController < ApplicationController
def new
#message = Message.new
end
def create
#message.sender_id = current_user
#message.recipient_id = current_user.friendships.friend_id
#message = Message.new(message_params)
if #message.save?
flash[:success] = 'Message sent successfully'
redirect_to welcome_profile_path
else
render 'new'
end
end
private
def message_params
params.require(:message).permit(:body, :sender_id, :recipient_id, :user_id)
end
end
messages/new.html.erb:
<h1>Create New Message</h1>
<%= simple_form_for #message do |f| %>
<%= f.input :body %>
<%#= f.association :user, :as => :hidden, :input_html => { :value => current_user.id }, :include_blank => false %>
<%= f.button :submit, "Send Message", class: "btn btn-secondary" %>
<% end %>
message.rb:
class Message < ActiveRecord::Base
belongs_to :user, foreign_key: :recipient_id
belongs_to :sender, :foreign_key => :sender_id, class_name: 'User'
belongs_to :recipient, :foreign_key => :recipient_id, class_name: 'User'
validates_presence_of :body
end
user.rb:
class User < ActiveRecord::Base
# Include default devise modules. Others available are:
# :confirmable, :lockable, :timeoutable and :omniauthable
devise :database_authenticatable, :registerable,
:recoverable, :rememberable, :trackable, :validatable
validates :username,
:presence => true,
:uniqueness => {
:case_sensitive => false
}
validate :validate_username
def validate_username
if User.where(email: username).exists?
errors.add(:username, :invalid)
end
end
has_many :friendships
has_many :friends, :through => :friendships
has_many :inverse_friendships, :class_name => "Friendship", :foreign_key => "friend_id"
has_many :inverse_friends, :through => :inverse_friendships, :source => :user
has_many :messages, dependent: :destroy
end
schema.rb:
ActiveRecord::Schema.define(version: 20160316170009) do
# These are extensions that must be enabled in order to support this database
enable_extension "plpgsql"
create_table "friendships", force: :cascade do |t|
t.integer "user_id"
t.integer "friend_id"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
create_table "messages", force: :cascade do |t|
t.text "body"
t.boolean "read"
t.integer "sender_id"
t.integer "recipient_id"
t.integer "user_id"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
add_index "messages", ["user_id"], name: "index_messages_on_user_id", using: :btree
create_table "users", force: :cascade do |t|
t.string "email", default: "", null: false
t.string "encrypted_password", default: "", null: false
t.string "reset_password_token"
t.datetime "reset_password_sent_at"
t.datetime "remember_created_at"
t.integer "sign_in_count", default: 0, null: false
t.datetime "current_sign_in_at"
t.datetime "last_sign_in_at"
t.inet "current_sign_in_ip"
t.inet "last_sign_in_ip"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.string "username"
end
add_index "users", ["email"], name: "index_users_on_email", unique: true, using: :btree
add_index "users", ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true, using: :btree
add_index "users", ["username"], name: "index_users_on_username", unique: true, using: :btree
add_foreign_key "messages", "users"
end

Answer 1

That error is because you don't have #message defined before setting #message.sender_id in your create action. Move #message = Message.new(message_params) to the top of the create action before setting #message.sender_id as follows:
class MessagesController < ApplicationController
...
def create
#message = Message.new(message_params)
#message.sender_id = current_user
#message.recipient_id = current_user.friendships.friend_id
if #message.save?
flash[:success] = 'Message sent successfully'
redirect_to welcome_profile_path
else
render 'new'
end
end
private
def message_params
params.require(:message).permit(:body, :sender_id, :recipient_id, :user_id)
end
end
The second part of the question - current_user is available in your controllers, so you don't need a hidden field for that. You can call #message.sender_id = current_user.id in your create action as you currently have. Next, to set #message.recipient_id, you could update your new.html.erb as follows:
# new.html.erb
<h1>Create New Message</h1>
<%= simple_form_for #message do |f| %>
<%= f.input :body %>
<%# Updated the following line. You could chose to create a hidden field here, or however you wish to implement this in your view as long as you specify `recipient` as the association or `recipient_id` as the field. %>
<%= f.association :recipient, :include_blank => false %>
<%= f.button :submit, "Send Message", class: "btn btn-secondary" %>
<% end %>
With the above setup your create action could be updated to:
# app/controllers/messages_controller.rb
def create
#message = Message.new(message_params)
#message.sender_id = current_user
if #message.save?
flash[:success] = 'Message sent successfully'
redirect_to welcome_profile_path
else
render 'new'
end
end