I have PCollection of type String and I want to transform this to get values of specific column from BigQuery table. So I used BigQueryIO.readTableRows to get values from BigQuery.

Here is my code:

     PCollection getConfigTable = pipeline.apply("read from Table",
            BigQueryIO.readTableRows().from("TableName"));

    RetrieveDestTableName retrieveDestTableName = new RetrieveDestTableName();
    PCollection getDestTableName = getConfigTable.apply(ParDo.of(new DoFn() {
        @ProcessElement
        public void processElement(ProcessContext c) {
            c.output(c.element().get("ColumnName").toString());
        }
    }));

As per above code I will get an output from getDestTableName of type PCollection, but I want this output in a String variable.

Is there any way to convert PCollection to String datatype variable so that I can able to use variable in my code?