Translate foreign key violations to ActiveRecord::InvalidForeignKey exceptions.

Signed-off-by: Michael Koziarski <michael@koziarski.com>

activerecord/lib/active_record/base.rb

@@ -71,6 +71,10 @@ module ActiveRecord #:nodoc:
   class RecordNotUnique < StatementInvalid
   end
 
+  # Raised when a record cannot be inserted or updated because it references a non-existent record.
+  class InvalidForeignKey < StatementInvalid
+  end
+
   # Raised when number of bind variables in statement given to <tt>:condition</tt> key (for example, when using +find+ method)
   # does not match number of expected variables.
   #

activerecord/lib/active_record/connection_adapters/mysql_adapter.rb

@@ -569,6 +569,8 @@ module ActiveRecord
           case exception.errno
           when 1062
             RecordNotUnique.new(message)
+          when 1452
+            InvalidForeignKey.new(message)
           else
             super
           end

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -945,6 +945,8 @@ module ActiveRecord
           case exception.message
           when /duplicate key value violates unique constraint/
             RecordNotUnique.new(message)
+          when /violates foreign key constraint/
+            InvalidForeignKey.new(message)
           else
             super
           end

activerecord/test/cases/adapter_test.rb

@@ -137,4 +137,12 @@ class AdapterTest < ActiveRecord::TestCase
       @connection.execute "INSERT INTO subscribers(nick) VALUES('me')"
     end
   end
+
+  def test_foreign_key_violations_are_translated_to_specific_exception
+    unless @connection.adapter_name == 'SQLite'
+      assert_raises(ActiveRecord::InvalidForeignKey) do
+        @connection.execute "INSERT INTO fk_test_has_fk (fk_id) VALUES (0)"
+      end
+    end
+  end
 end