title: Get the dynamoDB's primary key list
body: <p>I would like to extract the primary key of table to a list , but find no api to do that. </p>
  
  <p>for example, as the <a href="http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/SampleTablesAndData.html#ThreadBySubjectTableSchemaAndData" rel="noreferrer">amazon example thread table</a>, I want to ask how to : </p>
  
  <p>1) get the <code>hash primary key</code> list, in the <a href="http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/SampleTablesAndData.html#ThreadBySubjectTableSchemaAndData" rel="noreferrer">amazon example thread table</a> it would be an array of ["Amazon DynamoDB", "Amazon S3"]</p>
  
  <p>2) with assigning the <code>hash primary key</code> to "Amazon DynamoDB", I want to get the <code>range primary key</code> list and it would be an array of ["Amazon DynamoDB Thread 1", "Amazon DynamoDB Thread 2"]</p>