raises an exception on habtm join table inserts if join table contain…

…s a primary key. Caches this check to save time on subsequent inserts.

[#2086 state:committed]

Signed-off-by: Jeremy Kemper <jeremy@bitsweat.net>

activerecord/lib/active_record/associations/has_and_belongs_to_many_association.rb

@@ -1,6 +1,11 @@
 module ActiveRecord
   module Associations
     class HasAndBelongsToManyAssociation < AssociationCollection #:nodoc:
+      def initialize(owner, reflection)
+        super
+        @primary_key_list = {}
+      end
+
       def create(attributes = {})
         create_record(attributes) { |record| insert_record(record) }
       end
@@ -17,6 +22,12 @@ def reset_column_information
         @reflection.reset_column_information
       end
 
+      def has_primary_key?
+        return @has_primary_key unless @has_primary_key.nil?
+        @has_primary_key = (ActiveRecord::Base.connection.supports_primary_key? &&
+          ActiveRecord::Base.connection.primary_key(@reflection.options[:join_table]))
+      end
+
       protected
         def construct_find_options!(options)
           options[:joins]      = @join_sql
@@ -29,8 +40,9 @@ def count_records
         end
 
         def insert_record(record, force = true, validate = true)
-          if ActiveRecord::Base.connection.supports_primary_key? && ActiveRecord::Base.connection.primary_key(@reflection.options[:join_table])
-            raise ActiveRecord::ConfigurationError, "Primary key is not allowed in a has_and_belongs_to_many join table (#{@reflection.options[:join_table]})."
+          if has_primary_key?
+            raise ActiveRecord::ConfigurationError,
+              "Primary key is not allowed in a has_and_belongs_to_many join table (#{@reflection.options[:join_table]})."
           end
 
           if record.new_record?

activerecord/test/cases/associations/habtm_join_table_test.rb

@@ -8,7 +8,7 @@ class MyBook < ActiveRecord::Base
   has_and_belongs_to_many :my_readers
 end
 
-class JoinTableTest < ActiveRecord::TestCase
+class HabtmJoinTableTest < ActiveRecord::TestCase
   def setup
     ActiveRecord::Base.connection.create_table :my_books, :force => true do |t|
       t.string :name
@@ -42,4 +42,15 @@ def test_should_raise_exception_when_join_table_has_a_primary_key
       end
     end
   end
+
+  uses_transaction :test_should_cache_result_of_primary_key_check
+  def test_should_cache_result_of_primary_key_check
+    if ActiveRecord::Base.connection.supports_primary_key?
+      ActiveRecord::Base.connection.stubs(:primary_key).with('my_books_my_readers').returns(false).once
+      weaz = MyReader.create(:name=>'Weaz')
+
+      weaz.my_books << MyBook.create(:name=>'Great Expectations')
+      weaz.my_books << MyBook.create(:name=>'Greater Expectations')
+    end
+  end
 end