public DynamoDBMapperFieldModel<T,H> hashKey() {
        return this.model.hashKey();
    }
Gets the hash key field model for the specified type.
@param <H> The hash key type.
@return The hash key field model.
@throws DynamoDBMappingException If the hash key is not present.
aws-java-sdk-dynamodb/src/main/java/com/amazonaws/services/dynamodbv2/datamodeling/DynamoDBTableMapper.java