title: JSON table schema to bigquery.TableSchema for BigQuerySink
body: <p>I have a non-trivial table schema (involving nested and repeated fields) defined in JSON format (with the name, type, mode attributes) and stored in a file. It has been successfully used to populate a bigquery table with bq load command.</p>
  
  <p>But when I try to do the same thing with Dataflow Python SDK and BigQuerySink, the <code>schema</code> argument needs to be either a comma-separated list of <code>'name':'type'</code> elements, or a <code>bigquery.TableSchema</code> object.</p>
  
  <p>Is there any convenient way of getting my JSON schema to a <code>bigquery.TableSchema</code>, or do I have to transform it to a <code>name:value</code> list?</p>