code: public boolean isUnique(String columnName) {
          if (columnName == null) {
              return false;
          }
  
          for (IndexHolder ih : indexHoldersByName.values()) {
              if (ih.isUnique() && ih.getSize() == 1) {
                  if (ih.getIndexes().iterator().next().getColumnName().equalsIgnoreCase(columnName)) {
                      return true;
                  }
              }
          }
  
          return false;
      }
docs: /*
  Determine if the passed column is part of a unique index that has only 1 element, the passed column.