Question

我对卡桑德拉非常天真我正在使用astyanax

CREATE TABLE employees（empID int，deptID int，first_name varchar， last_name varchar，PRIMARY KEY（empID，deptID））;

我想获取查询的值：从empID = 2且deptID = 800;

的员工中选择*

     public void read(Integer empID, String deptID) {
    OperationResult<ColumnList<String>> result;
    try {

        columnFamilies = ColumnFamily.newColumnFamily("employees", IntegerSerializer.get(), StringSerializer.get()); 
      result = keyspace.prepareQuery(columnFamilies).getKey(empID).execute();

      ColumnList<String> cols = result.getResult();
 //Other stuff

}

我应该如何实现这个

Answer 1

据我所知，没有一种超级干净的方法可以做到这一点。您必须通过执行cql查询然后遍历行来执行此操作。此代码取自astynax examples file

public void read(int empId) {
  logger.debug("read()");
  try {
    OperationResult<CqlResult<Integer, String>> result
      = keyspace.prepareQuery(EMP_CF)
        .withCql(String.format("SELECT * FROM %s WHERE %s=%d;", EMP_CF_NAME, COL_NAME_EMPID, empId))
        .execute();
    for (Row<Integer, String> row : result.getResult().getRows()) {
      logger.debug("row: "+row.getKey()+","+row); // why is rowKey null?

      ColumnList<String> cols = row.getColumns();
      logger.debug("emp");
      logger.debug("- emp id: "+cols.getIntegerValue(COL_NAME_EMPID, null));
      logger.debug("- dept: "+cols.getIntegerValue(COL_NAME_DEPTID, null));
      logger.debug("- firstName: "+cols.getStringValue(COL_NAME_FIRST_NAME, null));
      logger.debug("- lastName: "+cols.getStringValue(COL_NAME_LAST_NAME, null));
    }
  } catch (ConnectionException e) {
    logger.error("failed to read from C*", e);
    throw new RuntimeException("failed to read from C*", e);
  }
}

您只需调整cql查询即可返回所需内容。这有点令人沮丧，因为根据文档，你可以做到

Column<String> result = keyspace.prepareQuery(CF_COUNTER1)
    .getKey(rowKey)
    .getColumn("Column1")
    .execute().getResult();
Long counterValue = result.getLongValue();

但我不知道rowkey是什么。我发布了a question about what rowkey can be。希望这会有所帮助

通过astyanax从复合键中检索数据

1 个答案: