Get models by ID from the database using SQLAlchemy

Using the model class's query attribute, we have access to two very handy methods:

ItemModel.query.get(item_id) gives us an ItemModel object from the database where the item_id matches the primary key.
ItemModel.query.get_or_404(item_id) does the same, but makes Flask immediately return a "Not Found" message, together with a 404 error code, if no model can be found with that ID in the database.

tip

When we use .get_or_404() and nothing is found, this is the response from the API:

{"code": 404, "status": "Not Found"}

The status code of this response is also 404.

We're going to use .get_or_404() repeatedly in our resources!

For now, and since we'll need an ItemModel instance in all our Item resource methods, let's add that:

resources/item.py
@blp.route("/items/<string:item_id>")
class Item(MethodView):
    @blp.response(200, ItemSchema)
    def get(self, item_id):
        item = ItemModel.query.get_or_404(item_id)
        return item

    def delete(self, item_id):
        item = ItemModel.query.get_or_404(item_id)
        raise NotImplementedError("Deleting an item is not implemented.")

    @blp.arguments(ItemUpdateSchema)
    @blp.response(200, ItemSchema)
    def put(self, item_data, item_id):
        item = ItemModel.query.get_or_404(item_id)
        raise NotImplementedError("Updating an item is not implemented.")

Similarly in our Store resource:

resources/store.py
@blp.route("/stores/<string:store_id>")
class Store(MethodView):
    @blp.response(200, StoreSchema)
    def get(self, store_id):
        store = StoreModel.query.get_or_404(store_id)
        return store

    def delete(self, store_id):
        store = StoreModel.query.get_or_404(store_id)
        raise NotImplementedError("Deleting a store is not implemented.")

With this, we're ready to continue!