code: public DbDatum getClassPipeProperty(String className, String pipeName, String propertyName) throws DevFailed {
          DbPipe dbPipe = databaseDAO.getClassPipeProperties(this, className, pipeName);
          DbDatum datum = dbPipe.getDatum(propertyName);
          if (datum==null)
              Except.throw_exception("TangoApi_PropertyNotFound",
                      "Property " + propertyName + " not found for pipe " + pipeName);
          return datum;
      }
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