private static PartitionKey determinePartitionKey()

in spanner-data-validator-java/src/main/java/com/google/migration/TableSpecList.java [336:398]
49 lines of code
10 McCabe index (conditional complexity)

  private static PartitionKey determinePartitionKey(SourceTable sourceTable, SpannerTable spannerTable) {
    PartitionKey partitionKey = null;

    //Store the column at the first ordinal position of the PK at Spanner
    ColumnPK[] spannerPKs = spannerTable.getPrimaryKeys();
    Arrays.sort(spannerPKs, Comparator.comparingInt(ColumnPK::getOrder));
    ColumnPK spannerPKAtFirstPosition = spannerPKs[0];


    //Get the ID and data type of the column in the first ordinal position of the source PK
    ColumnPK[] sourcePKs = sourceTable.getPrimaryKeys();
    if (sourcePKs.length == 0) {
      LOG.info("Source table does not have a PK, skipping validation");
      return  null;
    }
    Arrays.sort(sourcePKs, Comparator.comparingInt(ColumnPK::getOrder));
    ColumnPK sourcePKAtFirstPosition = sourcePKs[0];
    String sourcePKAtFirstPositionDataType = sourceTable.getColDefs().get(sourcePKAtFirstPosition.getColId()).getType().getName();

    //Check if source and spanner PK can be used to find PK.
    if (sourcePKAtFirstPosition.getColId().equals(spannerPKAtFirstPosition.getColId())) {
      partitionKey = createPartitionKey(sourcePKAtFirstPosition.getColId(), sourcePKAtFirstPositionDataType);
    }
    //No match with Spanner PK, check against indexes on spanner table
    if (partitionKey == null) {
      LOG.info("###########(Source PK, Spanner PK) -> No partition key found###########");
      partitionKey = searchSpannerIndexesForPartitionKey(sourcePKAtFirstPosition.getColId(), sourcePKAtFirstPositionDataType,
          spannerTable.getIndexes());
      }

    //source PK did not match with any PK or index at Spanner, check if any source indexes
    //can be used as a partitioning key
    if (partitionKey == null) {
      LOG.info("###########(Source PK, Spanner Indexes) -> No partition key found###########");
      Index[] sourceIndexes = sourceTable.getIndexes();
      if (sourceIndexes != null) {
        for (Index sourceIndex: sourceIndexes) {
          Arrays.sort(sourceIndex.getKeys(), Comparator.comparingInt(IndexKey::getOrder));
          IndexKey sourceIndexAtFirstPosition = sourceIndex.getKeys()[0];
          String sourceIndexAtFirstPositionDataType = sourceTable.getColDefs()
              .get(sourceIndexAtFirstPosition.getColId()).getType().getName();
          //first check with spanner PK
          if (sourceIndexAtFirstPosition.getColId().equals(spannerPKAtFirstPosition.getColId())) {
            partitionKey = createPartitionKey(sourceIndexAtFirstPosition.getColId(),
                sourceIndexAtFirstPositionDataType);
          }
          //if not found, check spanner indexes
          if (partitionKey == null) {
            LOG.info("###########(Source Indexes, Spanner PK) -> No partition key found###########");
            partitionKey = searchSpannerIndexesForPartitionKey(sourceIndexAtFirstPosition.getColId(),
                sourceIndexAtFirstPositionDataType, spannerTable.getIndexes());
          }
        }
      }

    }
    if (partitionKey == null) {
      LOG.info("###########(Source Indexes, Spanner Indexes) -> No partition key found###########");
      LOG.info("No suitable partitioning key was found for Source table: {}, Spanner table: {}", sourceTable.getName(), spannerTable.getName());
      LOG.info("Only (int, bigint) partition keys are supported, with a the following condition: There should exist an index (PK or secondary index) whose first ordinal position is a supported partitioning data type and is identical between source and spanner");
    }
    return partitionKey;
  }