The error occurred while evaluating nil.prefetch_primary_key

Rails
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:increate_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:increate_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:insave_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:insave_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:inwith_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:intransaction’
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:insave’
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:insave’
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!