Don't store defaults in the schema cache

activerecord/lib/active_record/attribute_methods/primary_key.rb

@@ -72,8 +72,8 @@ def get_primary_key(base_name) #:nodoc:
           when :table_name_with_underscore
             base_name.foreign_key
           else
-            if ActiveRecord::Base != self && connection.schema_cache.table_exists?(table_name)
-              connection.primary_key(table_name)
+            if ActiveRecord::Base != self && table_name
+              connection.schema_cache.primary_keys[table_name]
             else
               'id'
             end

activerecord/lib/active_record/connection_adapters/schema_cache.rb

@@ -8,7 +8,7 @@ def initialize(conn)
         @connection = conn
         @tables     = {}
 
-        @columns     = Hash.new do |h, table_name|
+        @columns = Hash.new do |h, table_name|
           h[table_name] = conn.columns(table_name, "#{table_name} Columns")
         end
 
@@ -19,8 +19,7 @@ def initialize(conn)
         end
 
         @primary_keys = Hash.new do |h, table_name|
-          h[table_name] = table_exists?(table_name) ?
-                          conn.primary_key(table_name) : 'id'
+          h[table_name] = table_exists?(table_name) ? conn.primary_key(table_name) : nil
         end
       end
 

activerecord/test/cases/base_test.rb

@@ -1494,6 +1494,7 @@ def test_set_primary_key_with_block
   def test_original_primary_key
     k = Class.new(ActiveRecord::Base)
     def k.name; "Foo"; end
+    k.table_name = "posts"
     k.primary_key = "bar"
 
     assert_deprecated do

activerecord/test/cases/connection_adapters/schema_cache_test.rb

@@ -13,7 +13,7 @@ def test_primary_key
       end
 
       def test_primary_key_for_non_existent_table
-        assert_equal 'id', @cache.primary_keys['omgponies']
+        assert_nil @cache.primary_keys['omgponies']
       end
 
       def test_caches_columns