I have a typescript interface describing mongodb database data like :

```
interface Foo {
  _id: string,
  name: string,

  fish: {
    _id: string,
    name: string,   
  },
}

```

I have a method that is building one data to insert in the database, like :

```
function pushNewFish() {
   const obj: Foo = {
      name: 'obiwan',

      fish: {
         name: 'kenobi',
      },
  };

  // ...
}

```

**The problem is** : I do not implements every `_id` elements that are specific to database.

I have the possibility to use `Partial<Foo>` but it's not what I'm looking for.

I also have the possibility to turn every `_id: string` into `_id ?: string`, but it feels wrong.

Is there a way to do : 

```
interface FooDatabase { ... }

type Foo = Partial<'_id', FooDatabase>;

```

? Thanks