Remove `klass` and `arel_table` as a dependency of `PredicateBuilder`

This class cares far too much about the internals of other parts of
Active Record. This is an attempt to break out a meaningful object which
represents the needs of the predicate builder. I'm not fully satisfied
with the name, but the general concept is an object which represents a
table, the associations to/from that table, and the types associated
with it. Many of these exist at the `ActiveRecord::Base` class level,
not as properties of the table itself, hence the need for another
object. Currently it provides these by holding a reference to the class,
but that will likely change in the future. This allows the predicate
builder to remain wholy concerned with building predicates.

/cc @mrgilman

1 files changed, 6 insertions, 2 deletions

diff --git a/activerecord/lib/active_record/core.rb b/activerecord/lib/active_record/core.rb
index 65ca1f6fd3..cb53fb0d44 100644
--- a/activerecord/lib/active_record/core.rb
+++ b/activerecord/lib/active_record/core.rb
@@ -249,12 +249,12 @@ module ActiveRecord
       end
 
       def predicate_builder # :nodoc:
-        @predicate_builder ||= PredicateBuilder.new(self, arel_table)
+        @predicate_builder ||= PredicateBuilder.new(table_metadata)
       end
 
       private
 
-      def relation #:nodoc:
+      def relation # :nodoc:
         relation = Relation.create(self, arel_table, predicate_builder)
 
         if finder_needs_type_condition?
@@ -263,6 +263,10 @@ module ActiveRecord
           relation
         end
       end
+
+      def table_metadata # :nodoc:
+        TableMetadata.new(self, arel_table)
+      end
     end
 
     # New objects can be instantiated as either empty (pass no construction parameter) or pre-set with