Question

Basically I have a One-To Many relationship between Alert and Updates. Many Updates belong to one Alert. Now my problem is that I cannot update any records in my database. I can create a new record without problems. Rails logger prints me the actual record to the logs. As you can see from the log files @new_alert retrieves the changed record, which should be saved to the database. Although it says “Alert was succesfully updated” it doesn’t update the old record with the new one. When I remove the relationship between Alert and Update then it works perfectly. I guess I have missed something in the Alert or Update model.

alerts_controller.rb
…

def update
@alert = Alert.find(params[:id])
    @new_alert = params[:alert]

    Rails.logger.debug "alert_params: #{@new_alert.inspect}"
    Rails.logger.debug "alert_db: #{@alert.inspect}"


respond_to do |format|
  if @alert.update_attributes(params[:alert])
    format.html { redirect_to @alert, notice: 'Alert was successfully updated.' }
    format.json { head :no_content }
  else
    format.html { render action: "edit" }
    format.json { render json: @alert.errors, status: :unprocessable_entity }
  end
end 
end...

Alert.rb

class Alert < ActiveRecord::Base
  has_many :update  
  accepts_nested_attributes_for :update
end

Update.rb

class Update < ActiveRecord::Base
belongs_to :alert, :foreign_key => 'alert_id'  
end

(MySQL) alerts table:

CREATE TABLE `alerts` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `status_id` int(11) DEFAULT NULL,
  `date` datetime DEFAULT NULL,
  `text` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  `title` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  `update_id` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)

(MySQL) updates table:

CREATE TABLE `updates` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `alert_id` int(11) DEFAULT NULL,
  `text` varchar(255) COLLATE utf8_unicode_ci DEFAULT NULL,
  `date` datetime DEFAULT NULL,
  PRIMARY KEY (`id`)

Log output:

Started PUT "/alerts/4" for 127.0.0.1 at 2012-08-24 15:47:12 +0200
Processing by AlertsController#update as HTML
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"GHM+S34PV4o46SpZZm67+mM8Lu9eY/BiWGMjDpwju9c=", "alert"=>{"title"=>"afgaegafga56556", "text"=>"afgafgafgarg", "status_id"=>"2"}, "commit"=>"Update Alert", "id"=>"4"}
  [1m[35mAlert Load (0.5ms)[0m  SELECT `alerts`.* FROM `alerts` WHERE `alerts`.`id` = 4 LIMIT 1
alert_params: {"title"=>"afgaegafga56556", "text"=>"afgafgafgarg", "status_id"=>"2"}
alert_db: #<Alert id: 4, status_id: 2, date: "2012-08-22 20:00:19", text: "afgafgafgarg", title: "afgaegafga", update_id: 1>
  [1m[36m (0.0ms)[0m  [1mBEGIN[0m
  [1m[35mUpdate Load (0.5ms)[0m  SELECT `updates`.* FROM `updates` WHERE `updates`.`alert_id` = 4
  [1m[36m (0.5ms)[0m  [1mCOMMIT[0m
Redirected to http://localhost:3000/alerts/4
Completed 302 Found in 4ms (ActiveRecord: 1.5ms)

Thanks!

Answer 1

has_many :update should be plural: has_many :updates otherwise the relation probably won’t work.

The same is true for accepts_nested_attributes_for.

Also (not significant but maybe good to know) you don’t have to define a foreign key when it matches the relationship name. So belongs_to :alert, :foreign_key => 'alert_id' is exactly the same as belongs_to :alert.