Add ability to specify how a class is converted to Arel predicate

This adds the ability for rails apps or gems to have granular control
over how a domain object is converted to sql. One simple use case would
be to add support for Regexp. Another simple case would be something
like the following:

    class DateRange < Struct.new(:start, :end)
      def include?(date)
        (start..end).cover?(date)
      end
    end

    class DateRangePredicate
      def call(attribute, range)
        attribute.in(range.start..range.end)
      end
    end

    ActiveRecord::PredicateBuilder.register_handler(DateRange,
      DateRangePredicate.new)

More complex cases might include taking a currency object and converting
it from EUR to USD before performing the query.

By moving the existing handlers to this format, we were also able to
nicely refactor a rather nasty method in PredicateBuilder.

1 files changed, 10 insertions, 0 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 61dba12b64..8f7f30167d 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,13 @@
+*   Add ability to define how a class is converted to Arel predicates.
+    For example, adding a very vendor specific regex implementation:
+
+        regex_handler = proc do |column, value|
+          Arel::Nodes::InfixOperation.new('~', column, value.source)
+        end
+        ActiveRecord::PredicateBuilder.register_handler(Regexp, regex_handler)
+
+    *Sean Griffin & @joannecheng*
+
 *   Don't allow `quote_value` to be called without a column.
 
     Some adapters require column information to do their job properly.