1 files changed, 28 insertions, 8 deletions
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb
index a11dbe7dce..4afb4733eb 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb
@@ -11,11 +11,22 @@ module ActiveRecord
         #     t.timestamps
         #   end
         #
-        # By default, this will use the +uuid_generate_v4()+ function from the
-        # +uuid-ossp+ extension, which MUST be enabled on your database. To enable
-        # the +uuid-ossp+ extension, you can use the +enable_extension+ method in your
-        # migrations. To use a UUID primary key without +uuid-ossp+ enabled, you can
-        # set the +:default+ option to +nil+:
+        # By default, this will use the +gen_random_uuid()+ function from the
+        # +pgcrypto+ extension. As that extension is only available in
+        # PostgreSQL 9.4+, for earlier versions an explicit default can be set
+        # to use +uuid_generate_v4()+ from the +uuid-ossp+ extension instead:
+        #
+        #   create_table :stuffs, id: false do |t|
+        #     t.primary_key :id, :uuid, default: "uuid_generate_v4()"
+        #     t.uuid :foo_id
+        #     t.timestamps
+        #   end
+        #
+        # To enable the appropriate extension, which is a requirement, use
+        # the +enable_extension+ method in your migrations.
+        #
+        # To use a UUID primary key without any of the extensions, set the
+        # +:default+ option to +nil+:
         #
         #   create_table :stuffs, id: false do |t|
         #     t.primary_key :id, :uuid, default: nil
@@ -23,15 +34,24 @@ module ActiveRecord
         #     t.timestamps
         #   end
         #
-        # You may also pass a different UUID generation function from +uuid-ossp+
-        # or another library.
+        # You may also pass a custom stored procedure that returns a UUID or use a
+        # different UUID generation function from another library.
         #
         # Note that setting the UUID primary key default value to +nil+ will
         # require you to assure that you always provide a UUID value before saving
         # a record (as primary keys cannot be +nil+). This might be done via the
         # +SecureRandom.uuid+ method and a +before_save+ callback, for instance.
         def primary_key(name, type = :primary_key, **options)
-          options[:default] = options.fetch(:default, "uuid_generate_v4()") if type == :uuid
+          if type == :uuid
+            options[:default] = options.fetch(:default, "gen_random_uuid()")
+          elsif options.delete(:auto_increment) == true && %i(integer bigint).include?(type)
+            type = if type == :bigint || options[:limit] == 8
+              :bigserial
+            else
+              :serial
+            end
+          end
+
           super
         end