Use hash[:Post][1] style identity maps for each table.

activerecord/lib/active_record/associations/association_proxy.rb

@@ -253,9 +253,9 @@ def method_missing(method, *args)
         def load_target
           return nil unless defined?(@loaded)
 
-          if !loaded? and (!@owner.persisted? || foreign_key_present)
-            if IdentityMap.enabled?
-              @target = IdentityMap.get(@reflection.class_name, @owner[@reflection.association_foreign_key])
+          if !loaded? and (@owner.persisted? || foreign_key_present)
+            if IdentityMap.enabled? && defined?(@reflection.klass)
+              @target = IdentityMap.get(@reflection.klass, @owner[@reflection.association_foreign_key])
             end
             @target ||= find_target
           end

activerecord/lib/active_record/base.rb

@@ -792,6 +792,10 @@ def ===(object)
         object.is_a?(self)
       end
 
+      def symbolized_base_class
+        @symbolized_base_class ||= base_class.to_s.to_sym
+      end
+
       # Returns the base AR subclass that this class descends from. If A
       # extends AR::Base, A.base_class will return A. If B descends from A
       # through some arbitrarily deep hierarchy, B.base_class will return A.
@@ -887,7 +891,10 @@ def instantiate(record)
           record_id = sti_class.primary_key && record[sti_class.primary_key]
 
           if ActiveRecord::IdentityMap.enabled? && record_id
-            if instance = identity_map.get(sti_class.name, record_id)
+            if (column = sti_class.columns_hash[sti_class.primary_key]) && column.number?
+              record_id = record_id.to_i
+            end
+            if instance = identity_map.get(sti_class, record_id)
               instance.reinit_with('attributes' => record)
             else
               instance = sti_class.allocate.init_with('attributes' => record)

activerecord/lib/active_record/identity_map.rb

@@ -23,7 +23,7 @@ class << self
       attr_accessor :enabled
 
       def current
-        repositories[current_repository_name] ||= Weakling::WeakHash.new
+        repositories[current_repository_name] ||= Hash.new { |h,k| h[k] = Weakling::WeakHash.new }
       end
 
       def with_repository(name = :default)
@@ -43,16 +43,20 @@ def without
         self.enabled = old
       end
 
-      def get(class_name, primary_key)
-        current[[class_name, primary_key.to_s]]
+      def get(klass, primary_key)
+        if obj = current[klass.symbolized_base_class][primary_key]
+          return obj if obj.id == primary_key && klass == obj.class
+        end
+
+        nil
       end
 
       def add(record)
-        current[[record.class.name, record.id.to_s]] = record
+        current[record.class.symbolized_base_class][record.id] = record
       end
 
       def remove(record)
-        current.delete([record.class.name, record.id.to_s])
+        current[record.class.symbolized_base_class].delete(record.id)
       end
 
       def clear

activerecord/test/cases/identity_map_test.rb

@@ -53,6 +53,13 @@ def test_find_by_id
     )
   end
 
+  def test_find_by_string_and_numeric_id
+    assert_same(
+      Client.find_by_id("3"),
+      Client.find_by_id(3)
+    )
+  end
+
   def test_find_by_pkey
     assert_same(
       Subscriber.find_by_nick('swistak'),