[source, ruby]
----
response = client.indices.create(
  index: 'my-index-000001',
  body: {
    mappings: {
      properties: {
        "my-join-field": {
          type: 'join',
          relations: {
            parent: 'child'
          }
        }
      }
    }
  }
)
puts response
----
