How to use default constructor for nested model

[davetapley]

If I have an array, I can call create() and get empty array:

const Thing = types.model({idx: types.identifier});
const Store = types.model({things: types.array(Thing)})

const store = Store.create();

But if I have a parent object:

const Thing = types.model({idx: types.identifier});
const Store = types.model({things: types.array(Thing)})
const Root = types.model({thingStore: Store})

const root = Root.create();

// Error while converting `{}` to `AnonymousModel`

I can fix with:

Root.create({ thingStore: {} });

But it would be nice if the the default empty constructor would be invoked automatically.

Am I missing something? 🤔

[EmilTholin]

Hi @davetapley!

As the Miscellaneous Tips part of the documenatation states types.array(Thing) is the same thing as types.optional(types.array(Thing), []), but that's not the case for types.model.

You have to explicitly set it to types.optional(Store, {}) for it to work the way you would like:

const Thing = types.model({ idx: types.identifier });
const Store = types.model({ things: types.array(Thing) });
const Root = types.model({ thingStore: types.optional(Store, {}) });

const root = Root.create();

// Success!

[davetapley]

Thank you!

I think I was misled by optional because I was thinking of it as optional in the maybe undefined sense, not in the may be omitted from the snapshot sense.