The optional Table transform function will be invoked on read and write requests to transform data before reading or writing to the table. The transform function can be used for custom storage formats or to assist with data migrations. The transform function can modify the item as it sees fit and return the modified item. The invocation signature is:
Where operation is set to 'read' or 'write'. The params and properties are the original params and properties provided to the API call. When writing, the item will contain the already transformed properties by the internal transformers. You can overwrite the value in item using your own custom transformation logic using property values from properties.
When reading, the item will contain the already transformed read data and the raw parameter will contain the raw data as read from the table before conversion into Javascript properties in item via the internal transformers.
You can also use a params.transform with many Model APIs. See Model Transformations for details.