Cassandra Java驱动程序查询结果集未存储在变量中
//Read data from Cassandra
String query = "SELECT * FROM LABA_2.DATA LIMIT 5;";
//Creating Cluster object
Cluster cluster = Cluster.builder().addContactPoint("127.0.0.1").build();
//Creating Session object
Session session = cluster.connect();
//Getting the ResultSet
ResultSet result = session.execute(query);
System.out.println(result.all().size());
System.out.println("AJFGJKABGSDKGJS");
System.out.println(result.all().size());
System.out.println("AJFGJKABGSDKGJS");
输出：
22/04/02 23:11:56 INFO Cluster: New Cassandra host /127.0.0.1:9042 added
5
AJFGJKABGSDKGJS
0
AJFGJKABGSDKGJS
第一种情况大小 = 5，第二种情况 = 0。
cassandra-driver - 3.11.0
为什么结果不同？
//Read data from Cassandra
String query = "SELECT * FROM LABA_2.DATA LIMIT 5;";
//Creating Cluster object
Cluster cluster = Cluster.builder().addContactPoint("127.0.0.1").build();
//Creating Session object
Session session = cluster.connect();
//Getting the ResultSet
ResultSet result = session.execute(query);
System.out.println(result.all().size());
System.out.println("AJFGJKABGSDKGJS");
System.out.println(result.all().size());
System.out.println("AJFGJKABGSDKGJS");
Output:
22/04/02 23:11:56 INFO Cluster: New Cassandra host /127.0.0.1:9042 added
5
AJFGJKABGSDKGJS
0
AJFGJKABGSDKGJS
In the first case size = 5, in the second = 0.
cassandra-driver - 3.11.0
Why results are different?
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评论（1）
您的测试无效。调用
resultset.all（）迫使驱动程序一口气检索整个结果设置。重要的是，这里要注意的是，在调用all（）之后，没有什么可检索的。当您第二次调用
all（）时，它没有返回，因为您已经检索了所有内容 - 列表已经耗尽了，没有剩下的。干杯!Your test is invalid. Calling
ResultSet.all()forces the driver to retrieve the whole result set in one go. The important thing to note here is that after callingall(), there is nothing left to retrieve.When you call
all()a second time, it returns nothing because you have already retrieved everything -- the list is exhausted and there's nothing left. Cheers!