Nested form renders decimal instead of fixnum when using Oracle, JRuby - oracle

Question

When using nested forms with Oracle DB, Rails renders a decimal/float (e.g. 10010.0) instead of a fixnum (e.g. 10010) for all integer fields, including the id field, resulting in exceptions when updating. With SQLite it works as expected.
Why does this happen and where do things go wrong??
The following code demonstrates the issue:
Models
class Broker < ActiveRecord::Base
has_many :execution_groups, dependent: :destroy
accepts_nested_attributes_for :execution_groups, allow_destroy: true
end
class ExecutionGroup < ActiveRecord::Base
belongs_to :broker
end
View
= form_for( #broker, html: { class: 'form-horizontal'} ) do |f|
= f.fields_for :execution_groups, include_id: true do |eg_form|
= eg_form.hidden_field :id
Result in Browser when using SQLite
...
<input id="broker_execution_groups_attributes_0_id"
name="broker[execution_groups_attributes][0][id]"
type="hidden"
value="10010" />
...
This works as expected, the nested model is updated.
Result in Browser when using Oracle
...
<input id="broker_execution_groups_attributes_1_id"
name="broker[execution_groups_attributes][1][id]"
type="hidden"
value="10010.0" />
...
This crashes with a neat exception:
ActiveRecord::RecordNotFound in BrokersController#update
Couldn't find ExecutionGroup with ID=10010.0 for Broker with ID=10040
As to be expected, AR's not finding an ID like 10010.0 because there's only ID 10010 (without the .0) available.
Current Environment
.ruby-version (rvm configuration file)
jruby-1.7.19
Gemsfile.lock (excerpt)
rails (4.0.13)
actionmailer (= 4.0.13)
actionpack (= 4.0.13)
activerecord (= 4.0.13)
activesupport (= 4.0.13)
bundler (>= 1.3.0, < 2.0)
railties (= 4.0.13)
sprockets-rails (~> 2.0)
railties (4.0.13)
actionpack (= 4.0.13)
activesupport (= 4.0.13)
rake (>= 0.8.7)
thor (>= 0.18.1, < 2.0)
activerecord-jdbc-adapter (1.3.19)
activerecord (>= 2.2)
activerecord-jdbcsqlite3-adapter (1.3.19)
activerecord-jdbc-adapter (~> 1.3.19)
jdbc-sqlite3 (>= 3.7.2, < 3.9)
jdbc-sqlite3 (3.8.11.2)
config/database.yml
Oracle via JDBC
development:
url: jdbc:oracle:thin:#mydbhost:1522:myschema
username: myuser
password: secret
SQLite
development:
adapter: sqlite3
database: db/development.sqlite3

Answer 1

Solution
Digging deeper into ActiveRecord I found that specifically overwriting the id_before_type_cast method for the model does the trick:
class ExecutionGroup < ActiveRecord::Base
belongs_to :broker
def id_before_type_cast
Integer( self.id ) unless self.id.nil?
end
end
While this does the trick, the *_before_type_cast needs to be defined for any Fixnum column or you'll get the same problem with the values.
Debugging details:
Stepping into ActionView::Helpers::Tags::Base.value_before_type_cast(object) I get the following status:
# for both SQLite and Oracle
object.class == ExecutionGroup # -> true
object.respond_to?(method_before_type_cast) # -> true
# SQLite
object.id_before_type_cast # -> {Fixnum} 10010
# Oracle
object.id_before_type_cast # -> {BigDecimal} 10010.0
After applying the fix both Oracle and SQLite show the same behaviour.
object.id_before_type_cast # -> {Fixnum} 10010