The error occurred while evaluating nil.prefetch_primary_key

rubyonrails-talk
1

The error occurred while evaluating nil.prefetch_primary_key?

Hi,

I have a problem with a model when I have 3 belongs_to relations in one the middle.

This example is a subset of a grid-routing project:

                         n 1            1 n +------------ Project Connection ------- ConnectionCost                         +------------ WaySearchRun                          n 1 The Problem is, when I add the 'belongs_to' in ConnectionCost. I get the following error-message after creating a ConnectionCost :

ConnectionCost.create

NoMethodError: You have a nil object when you didn't expect it! The error occurred while evaluating nil.prefetch_primary_key?   from /home/markus/Development/GPT2/my_test2/vendor/rails/activerecord/lib/active_record/base.rb:2721:in `create_without_callbacks'   from /home/markus/Development/GPT2/my_test2/vendor/rails/activerecord/lib/active_record/callbacks.rb:237:in `create_without_timestamps'   from /home/markus/Development/GPT2/my_test2/vendor/rails/activerecord/lib/active_record/timestamp.rb:29:in `create'   from /home/markus/Development/GPT2/my_test2/vendor/rails/activerecord/lib/active_record/base.rb:2701:in `create_or_update_without_callbacks'   from /home/markus/Development/GPT2/my_test2/vendor/rails/activerecord/lib/active_record/callbacks.rb:222:in `create_or_update'   from /home/markus/Development/GPT2/my_test2/vendor/rails/activerecord/lib/active_record/base.rb:2385:in `save_without_validation'   from /home/markus/Development/GPT2/my_test2/vendor/rails/activerecord/lib/active_record/validations.rb:1009:in `save_without_dirty'   from /home/markus/Development/GPT2/my_test2/vendor/rails/activerecord/lib/active_record/dirty.rb:79:in `save_without_transactions'   from /home/markus/Development/GPT2/my_test2/vendor/rails/activerecord/lib/active_record/transactions.rb:179:in `send'   from /home/markus/Development/GPT2/my_test2/vendor/rails/activerecord/lib/active_record/transactions.rb:179:in `with_transaction_returning_status'   from /home/markus/Development/GPT2/my_test2/vendor/rails/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb:66:in `transaction'   from /home/markus/Development/GPT2/my_test2/vendor/rails/activerecord/lib/active_record/transactions.rb:129:in `transaction'   from /home/markus/Development/GPT2/my_test2/vendor/rails/activerecord/lib/active_record/transactions.rb:178:in `with_transaction_returning_status'   from /home/markus/Development/GPT2/my_test2/vendor/rails/activerecord/lib/active_record/transactions.rb:146:in `save'   from /home/markus/Development/GPT2/my_test2/vendor/rails/activerecord/lib/active_record/transactions.rb:158:in `rollback_active_record_state!'   from /home/markus/Development/GPT2/my_test2/vendor/rails/activerecord/lib/active_record/transactions.rb:146:in `save'   from /home/markus/Development/GPT2/my_test2/vendor/rails/activerecord/lib/active_record/base.rb:693:in `create'   from (irb):5>>

For this test I created a new rails-project (version 2.2.3).

Models :

class Connection < ActiveRecord::Base   has_many :connection_costs end

class Project < ActiveRecord::Base   has_many :connection_costs end

class WaySearchRun < ActiveRecord::Base   has_many :connection_costs end

class ConnectionCost < ActiveRecord::Base     belongs_to :connection # dosn't WORK !!!!     belongs_to :project     belongs_to :way_search_run end

Migrations :

class CreateConnections < ActiveRecord::Migration   def self.up     create_table :connections do |t|       t.string :name # Name       t.string :alias # Alias-Name       t.string :descr # Description       t.timestamps     end   end

  def self.down     drop_table :connections   end end

class CreateProjects < ActiveRecord::Migration   def self.up     create_table :projects do |t|       t.string :name # Name       t.string :descr # Description       t.timestamps     end   end

  def self.down     drop_table :projects   end end

class CreateWaySearchRuns < ActiveRecord::Migration   def self.up     create_table :way_search_runs do |t|       t.string :name # Name       t.string :descr # Description       t.integer :sort_number # for sorting - for a project in 10-steps       t.references :project # Link to an 'Project'       t.timestamps     end     add_index :way_search_runs, :project_id   end

  def self.down     drop_table :way_search_runs   end end

class CreateConnectionCosts < ActiveRecord::Migration   def self.up     create_table :connection_costs do |t|       t.decimal :cost ,:precision=>10,:scale=>4 ,:default=>100.0 # absolute Costs       t.decimal :cost_factor ,:precision=>10,:scale=>4 ,:default=>1.0 # CostFactor -> totalCosts = CostFactor * absCosts       t.references :connection # Link to an 'Connection'       t.references :project # Link to an 'Project'       t.references :way_search_run # Link to an 'WaySearchRun'       t.timestamps     end

    add_index :connection_costs, :connection_id     add_index :connection_costs, :project_id     add_index :connection_costs, :way_search_run_id

  end

  def self.down     drop_table :connection_costs   end end

Thanks!