private void setPrimaryKeys (List<String> primaryKeys) {
      // if primary keys empty and mode is incremental raise exception
      if ((primaryKeys == null || primaryKeys.isEmpty())
          && options.getMode().equals(ReplicationMode.INCREMENTAL.getModeText())) {
         throw new IllegalArgumentException("Sink collection \"" + getSinkTableName() + "\" must have at least one unique key index for incremental mode.");
      }
      LOG.info("Primary key fields: {}", primaryKeys);
      this.primaryKeys = primaryKeys;
   }
Constructs the SqlManager.

@param opts the ReplicaDB ToolOptions describing the user's requested action.
src/main/java/org/replicadb/manager/MongoDBManager.java