使用Python驱动程序检查Cassandra表中是否存在记录 [英] Check if a record exists in a Cassandra table using the Python driver

问题描述

如何确定表中是否存在记录？我尝试的方法是执行 SELECT 查询，然后使用以下方法计算 ResultSet 的行：

How can be determined whether a record exists in a table? The way I tried was to do a SELECT query and then count the rows of the ResultSet using the following:

rows = session.execute("SELECT * FROM test_table WHERE id=%s", ([<id_here>]))
if len(rows) == 0:
    print "Does not exist"

但是， ResultSet 不支持 len 。在另一个答案中，他们建议使用 SELECT COUNT（*）在另一个参考文献中强烈建议不要这样做。有更标准的方法可以做到这一点吗？

However, ResultSet does not support len. In another answer, they suggest to use SELECT COUNT(*) which in another reference is strongly discouraged. Is there a more standard way to do this?

推荐答案

您只需执行以下一项操作即可：

You can simply do one of the following:

rows = session.execute("SELECT * FROM test_table WHERE id=%s", ([<id_here>]))
if not rows:
    print "Does not exist"

或者，如果选择多行，则可以使用以下方法遍历ResultSet：

Or, if selecting multiple rows you could iterate over the ResultSet with:

for row in rows:
    do_something(row)

ResultSet还具有current_rows属性，如果未返回任何属性，则该属性为空。

ResultSet also has a current_rows attribute which will be empty if none were returned.

请参见 http://datastax.github.io/python-driver/api/cassandra/ cluster.html＃cassandra.cluster.ResultSet 有关如何使用ResultSet的更多详细信息。

See http://datastax.github.io/python-driver/api/cassandra/cluster.html#cassandra.cluster.ResultSet for more details on how to use the ResultSet.

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