Error: dynamodb list_append if_not_exists not working

What's Causing This Error

This is a generic error you may encounter when using the list_append or if_not_exists update expression functions. This error mainly occurs when you try to execute these two functions on child attributes where the parent does not exist.

const expression = SET #parent.#child = list_appends(if_not_exists(#parent.child,:emptyArray),:add))

The snippet below shows that a list item is appended to a property named child in the parent attribute.

However, if the parent attribute does not exist when this expression gets executed, DynamoDB will throw an error.

Solution: Here's How To Resolve It

To resolve the error, ensure that the parent (top level) attribute exists in the item before managing a child attribute.

// ensure that the item has an attribute named parent
#parent.#child