# Adding shared properties

One common pattern in applications is to add shared properties to the schema that are used by multiple objects. For example, you might want to add a `created_at` and `updated_at` property to every object in your schema. You can do this by adding an abstract type and using it as a mixin for your other object types.

- dbschema/default.gel:
  ```sdl-diff
    module default {
  +   abstract type Timestamped {
  +     required created_at: datetime {
  +       default := datetime_of_statement();
  +     };
  +     required updated_at: datetime {
  +       default := datetime_of_statement();
  +     };
  +   }
  +
  -   type Deck {
  +   type Deck extending Timestamped {
        required name: str;
        description: str;
  
        cards := (
          select .<deck[is Card]
          order by .order
        );
      };
  
  -   type Card {
  +   type Card extending Timestamped {
        required order: int64;
        required front: str;
        required back: str;
  
        required deck: Deck;
      }
    }
  ```

Since you don't have historical data for when these objects were actually created or modified, the migration will fall back to the default values set in the `Timestamped` type.

```sh
$ gel migration create
did you create object type 'default::Timestamped'? [y,n,l,c,b,s,q,?]
> y
did you alter object type 'default::Card'? [y,n,l,c,b,s,q,?]
> y
did you alter object type 'default::Deck'? [y,n,l,c,b,s,q,?]
> y
Created /home/strinh/projects/flashcards/dbschema/migrations/00004-m1d2m5n.edgeql, id: m1d2m5n5ajkalyijrxdliioyginonqbtfzihvwdfdmfwodunszstya

$ gel migrate
Applying m1d2m5n5ajkalyijrxdliioyginonqbtfzihvwdfdmfwodunszstya (00004-m1d2m5n.edgeql)
... parsed
... applied
```

Update the `get_decks` query to sort the decks by `updated_at` in descending order.

- main.py:
  ```python-diff
    @app.get("/decks", response_model=List[Deck])
    async def get_decks():
        decks = await client.query("""
            select Deck {
                id,
                name,
                description,
                cards := (
                    select .cards {
                        id,
                        front,
                        back
                    }
                    order by .order
                )
            }
  +         order by .updated_at desc
        """)
        return decks
  ```