'Returns the schema structure DynamoDB expects.
Example::
>>> index.schema()
\'IndexName\': \'LastNameIndex\',
\'KeySchema\': [
\'AttributeName\': \'username\',
\'KeyType\': \'HASH\',
\'Projection\': {
\'ProjectionType\': \'KEYS_ONLY\',
\'ProvisionedThroughput\': {
\'ReadCapacityUnits\': 5,
\'WriteCapacityUnits\': 5'

def schema(self):

    schema_data = super(GlobalBaseIndexField, self).schema()
    schema_data['ProvisionedThroughput'] = {'ReadCapacityUnits': int(self.throughput['read']), 'WriteCapacityUnits': int(self.throughput['write'])}
    return schema_data
