BulkLoader -export_transform

I have created web application using java.I wantted to download data from appengine datastroe so that I am using BulkLoader concept.

In my project I designed entity as follows

@Id

@GeneratedValue(strategy = GenerationType.IDENTITY)

private Long school_id;

@Basic

private String schoolname;

After that I tried to download data so that I created bulkloader configuration file .It created successfully but I that default auto generated bulkloade.yaml file I have one problem(i.E)export-transform convert Primary key into string, but I need Long datatype how to achieve this.

The content of bulkloader file is

- kind: School

  connector: csv

  property_map:

    - property: __key__

      external_name: key

      export_transform: transform.key_id_or_name_as_string

    - property: schoolname

      external_name: schoolname

How to solve this Thanks in advance

Try export_transform: datastore.Key.name