2 files changed, 13 insertions, 4 deletions
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
index 42bd16db80..1da95f451f 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
@@ -441,11 +441,11 @@ module ActiveRecord
       end
 
       def new_connection
-        ActiveRecord::Model.send(spec.adapter_method, spec.config)
+        Base.send(spec.adapter_method, spec.config)
       end
 
       def current_connection_id #:nodoc:
-        ActiveRecord::Model.connection_id ||= Thread.current.object_id
+        Base.connection_id ||= Thread.current.object_id
       end
 
       def checkout_new_connection
@@ -567,10 +567,10 @@ module ActiveRecord
         class_to_pool[klass] ||= begin
           until pool = pool_for(klass)
             klass = klass.superclass
-            break unless klass < ActiveRecord::Tag
+            break unless klass <= Base
           end
 
-          class_to_pool[klass] = pool || pool_for(ActiveRecord::Model)
+          class_to_pool[klass] = pool
         end
       end
 
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
index d61731633a..38960ab873 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
@@ -234,6 +234,10 @@ module ActiveRecord
         name = name.to_s
         type = type.to_sym
 
+        if primary_key_column_name == name
+          raise ArgumentError, "you can't redefine the primary key column '#{name}'. To define a custom primary key, pass { id: false } to create_table."
+        end
+
         column = self[name] || new_column_definition(@base, name, type)
 
         limit = options.fetch(:limit) do
@@ -302,6 +306,11 @@ module ActiveRecord
         definition
       end
 
+      def primary_key_column_name
+        primary_key_column = columns.detect { |c| c.type == :primary_key }
+        primary_key_column && primary_key_column.name
+      end
+
       def native
         @base.native_database_types
       end