1 files changed, 12 insertions, 4 deletions
diff --git a/activerecord/lib/active_record/connection_adapters/schema_cache.rb b/activerecord/lib/active_record/connection_adapters/schema_cache.rb
index dd6363cd2a..b516518126 100644
--- a/activerecord/lib/active_record/connection_adapters/schema_cache.rb
+++ b/activerecord/lib/active_record/connection_adapters/schema_cache.rb
@@ -1,7 +1,7 @@
 module ActiveRecord
   module ConnectionAdapters
     class SchemaCache
-      attr_reader :primary_keys, :tables, :version
+      attr_reader :tables, :version
       attr_accessor :connection
 
       def initialize(conn)
@@ -14,6 +14,14 @@ module ActiveRecord
         prepare_default_proc
       end
 
+      def primary_keys(table_name = nil)
+        if table_name
+          @primary_keys[table_name]
+        else
+          @primary_keys.dup
+        end
+      end
+
       # A cached lookup for table existence.
       def table_exists?(name)
         return @tables[name] if @tables.key? name
@@ -35,7 +43,7 @@ module ActiveRecord
         if table
           @columns[table]
         else
-          @columns
+          @columns.dup
         end
       end
 
@@ -45,7 +53,7 @@ module ActiveRecord
         if table
           @columns_hash[table]
         else
-          @columns_hash
+          @columns_hash.dup
         end
       end
 
@@ -89,7 +97,7 @@ module ActiveRecord
         end
 
         @columns_hash.default_proc = Proc.new do |h, table_name|
-          h[table_name] = Hash[columns[table_name].map { |col|
+          h[table_name] = Hash[columns(table_name).map { |col|
             [col.name, col]
           }]
         end