How to create a cart when none exists?

[magnattic]

I am a bit lost with the new createCartHandler, I am trying to retrieve a cart or create one if it exists.

At first I tried the following approach:

const retrieveCart = async ({
  cart,
}: {
  cart: HydrogenCart;
}): Promise<Cart> => {
  const existingCart = await cart.get();
  if (existingCart !== null) {
    return existingCart;
  }

  return (await cart.create({ lines: [] })).cart;
};

This works somewhat, but the problem is that the mutation sent by cart.create() only queries an absolutely minimal cart with many of the basic things like lines missing. I need a more complete cart at this point.

My second approach was to create the cart and then try to query it with cart.get(), but that doesn't work:

const retrieveCart = async ({
  cart,
}: {
  cart: HydrogenCart;
}): Promise<Cart> => {
  const existingCart = await cart.get();
  if (existingCart !== null) {
    return existingCart;
  }

  const cartId = (await cart.create({ lines: [] })).cart.id;
  cart.setCartId(cartId);
  const createdCart = await cart.get({ cartId });
  if (createdCart == null) {
    throw new Error('Could not create cart');
  }
  return createdCart;
};

In this attempt, createdCart is always null.

What's the best practice for this?

[magnattic]

I have now followed this solution to set a fragment in the cart handler which queries the whole cart on cart mutation: https://shopify.dev/docs/custom-storefronts/hydrogen/cart/customize-cart-handler#customize-the-return-cart-fields

I'm just not sure if that is the best way. Does this also query all fields when a single line in the cart is updated? I just want to do this on cart creation.

[blittle]

@magnattic I recommend not creating a cart until it is needed. For example cart.createLines(...) optimistically creates a cart if one doesn't already exist. If someone visits your site, and they never interact with the cart, there's no reason to create one. This change should make it easier to query the cart right after it is created though: #1865