pg, support default values for enum types. Closes #7814.

This is an intermediate solution. It is related to the refactoring @sgrif
is making and will change in the future.

activerecord/CHANGELOG.md

+*   PostgreSQL support default values for enum types. Fixes #7814.
+
+    *Yves Senn*
+
 *   PostgreSQL `default_sequence_name` respects schema. Fixes #7516.
 
     *Yves Senn*

activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb

@@ -179,7 +179,7 @@ def columns(table_name)
           # Limit, precision, and scale are all handled by the superclass.
           column_definitions(table_name).map do |column_name, type, default, notnull, oid, fmod|
             oid = get_oid_type(oid.to_i, fmod.to_i, column_name, type)
-            default_value = extract_value_from_default(default)
+            default_value = extract_value_from_default(oid, default)
             default_function = extract_default_function(default_value, default)
             new_column(column_name, default_value, oid, type, notnull == 'f', default_function)
           end

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -498,7 +498,7 @@ def extract_limit(sql_type) # :nodoc:
         end
 
         # Extracts the value from a PostgreSQL column default definition.
-        def extract_value_from_default(default) # :nodoc:
+        def extract_value_from_default(oid, default) # :nodoc:
           # This is a performance optimization for Ruby 1.9.2 in development.
           # If the value is nil, we return nil straight away without checking
           # the regular expressions. If we check each regular expression,
@@ -507,6 +507,13 @@ def extract_value_from_default(default) # :nodoc:
           # makes this method very very slow.
           return default unless default
 
+          # TODO: The default extraction is related to the cast-type.
+          # we should probably make a type_map lookup and cast the default-
+          # expression accordingly
+          if oid.type == :enum && default =~ /\A'(.*)'::/
+            return $1
+          end
+
           case default
             when /\A'(.*)'::(num|date|tstz|ts|int4|int8)range\z/m
               $1

activerecord/test/cases/adapters/postgresql/enum_test.rb

@@ -39,6 +39,17 @@ def test_column
     assert_not column.array
   end
 
+  def test_enum_defaults
+    @connection.add_column 'postgresql_enums', 'good_mood', :mood, default: 'happy'
+    PostgresqlEnum.reset_column_information
+    column = PostgresqlEnum.columns_hash["good_mood"]
+
+    assert_equal "happy", column.default
+    assert_equal "happy", PostgresqlEnum.new.good_mood
+  ensure
+    PostgresqlEnum.reset_column_information
+  end
+
   def test_enum_mapping
     @connection.execute "INSERT INTO postgresql_enums VALUES (1, 'sad');"
     enum = PostgresqlEnum.first