Updating models with SQLAlchemy

A frequent operation in REST APIs is the "upsert", or "update or insert".

This is an idempotent operation where we send the data we want the API to store. If the data identifier already exists, an update is done. If it doesn't, it is created.

This idempotency is frequently seen with PUT requests. You can see it in action here:

resources/item.py

@blp.arguments(ItemUpdateSchema)
@blp.response(200, ItemSchema)
def put(self, item_data, item_id):
    item = ItemModel.query.get(item_id)
    if item:
        item.price = item_data["price"]
        item.name = item_data["name"]
    else:
        item = ItemModel(id=item_id, **item_data)

    db.session.add(item)
    db.session.commit()

    return item

Our ItemUpdateSchema at the moment looks like this:

schemas.py

class ItemUpdateSchema(Schema):
    name = fields.Str()
    price = fields.Float()

But since now our update endpoint may create items, we need to change the schema to optionally accept a store_id.

When updating an item, name or price (or both) may be passed, but when creating an item, name, price, and store_id must be passed.

Update the ItemUpdateSchema to this:

schemas.py

class ItemUpdateSchema(Schema):
    name = fields.Str()
    price = fields.Float()
    store_id = fields.Int()