index - edge index 

How to add an edge index.

Synopsis

index('index_name').[outE('edgeLabel') | inE('edgeLabel') ].by('propertykey_name').add()

Description

An edge index specifies an index that is built using an edge property key in DSE Graph. A vertex label must be specified. The index name must be unique.

Examples

Create an index ratedByStars with an outE edge label using the property key stars. The vertex label is specified as reviewer.
schema.vertexLabel('reviewer').index('ratedByStars').outE('rated').by('stars').add()