key 

How to designate the incoming a simple unique key to use when loading data from a data file.

Synopsis 

key "fieldName"

Description 

Each record read from an input data file must be unique to avoid duplication. key defines a simple unique key for this element comprised of a single field and associated property key name.

Examples 

Set the key in a mapping script to name.
key "name"
If the data file includes unique ids, such as a GraphSON or Gryo file written from DataStax Enterprise, the key can be set to identify the id:
key "~id" "id"
where ~id defines that the id is found in the data file, and id renames the field to id in the loaded file.