Fixed `where` for polymorphic associations when passed an array containing different types.

When passing in an array of different types of objects to `where`, it would only take into account the class of the first object in the array.

    PriceEstimate.where(estimate_of: [Treasure.find(1), Car.find(2)])
	# => SELECT "price_estimates".* FROM "price_estimates"
         WHERE ("price_estimates"."estimate_of_type" = 'Treasure' AND "price_estimates"."estimate_of_id" IN (1, 2))

This is fixed to properly look for any records matching both type and id:

    PriceEstimate.where(estimate_of: [Treasure.find(1), Car.find(2)])
    # => SELECT "price_estimates".* FROM "price_estimates"
         WHERE (("price_estimates"."estimate_of_type" = 'Treasure' AND "price_estimates"."estimate_of_id" = 1)
         OR ("price_estimates"."estimate_of_type" = 'Car' AND "price_estimates"."estimate_of_id" = 2))

2 files changed, 67 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/relation/predicate_builder/association_query_handler.rb b/activerecord/lib/active_record/relation/predicate_builder/association_query_handler.rb
index e81be63cd3..d7fd878265 100644
--- a/activerecord/lib/active_record/relation/predicate_builder/association_query_handler.rb
+++ b/activerecord/lib/active_record/relation/predicate_builder/association_query_handler.rb
@@ -1,6 +1,16 @@
 module ActiveRecord
   class PredicateBuilder
     class AssociationQueryHandler # :nodoc:
+      def self.value_for(table, column, value)
+        klass = if table.associated_table(column).polymorphic_association? && ::Array === value && value.first.is_a?(Base)
+          PolymorphicArrayValue
+        else
+          AssociationQueryValue
+        end
+
+        klass.new(table.associated_table(column), value)
+      end
+
       def initialize(predicate_builder)
         @predicate_builder = predicate_builder
       end
diff --git a/activerecord/lib/active_record/relation/predicate_builder/polymorphic_array_handler.rb b/activerecord/lib/active_record/relation/predicate_builder/polymorphic_array_handler.rb
new file mode 100644
index 0000000000..b6c6240343
--- /dev/null
+++ b/activerecord/lib/active_record/relation/predicate_builder/polymorphic_array_handler.rb
@@ -0,0 +1,57 @@
+module ActiveRecord
+  class PredicateBuilder
+    class PolymorphicArrayHandler # :nodoc:
+      def initialize(predicate_builder)
+        @predicate_builder = predicate_builder
+      end
+
+      def call(attribute, value)
+        table = value.associated_table
+        queries = value.type_to_ids_mapping.map do |type, ids|
+          { table.association_foreign_type.to_s => type, table.association_foreign_key.to_s => ids }
+        end
+
+        predicates = queries.map { |query| predicate_builder.build_from_hash(query) }
+
+        if predicates.size > 1
+          type_and_ids_predicates = predicates.map { |type_predicate, id_predicate| Arel::Nodes::Grouping.new(type_predicate.and(id_predicate)) }
+          type_and_ids_predicates.inject(&:or)
+        else
+          predicates.first
+        end
+      end
+
+      protected
+
+      attr_reader :predicate_builder
+    end
+
+    class PolymorphicArrayValue # :nodoc:
+      attr_reader :associated_table, :values
+
+      def initialize(associated_table, values)
+        @associated_table = associated_table
+        @values = values
+      end
+
+      def type_to_ids_mapping
+        default_hash = Hash.new { |hsh, key| hsh[key] = [] }
+        values.each_with_object(default_hash) { |value, hash| hash[base_class(value).name] << convert_to_id(value) }
+      end
+
+      private
+
+      def primary_key(value)
+        associated_table.association_primary_key(base_class(value))
+      end
+
+      def base_class(value)
+        value.class.base_class
+      end
+
+      def convert_to_id(value)
+        value._read_attribute(primary_key(value))
+      end
+    end
+  end
+end