Question

我正在使用一个片段来理解cassandra和语法：

import com.datastax.driver.core.Cluster;
import com.datastax.driver.core.ResultSet;
import com.datastax.driver.core.Row;
import com.datastax.driver.core.Session;

public class App {

    public static void main(String[] args) {

        Cluster cluster;
        Session session;

        // Connect to the cluster and key space "demo"
        cluster = Cluster.builder().addContactPoint("127.0.0.1").build();
        session = cluster.connect("demo");

        // Insert one record into the users table
        session.execute("INSERT INTO users (lastname, age, city, email, firstname) VALUES ('Jones', 35, 'Austin', 'bob@example.com', 'Bob')");

        // Use select to get the user we just entered
        ResultSet results = session.execute("SELECT * FROM users WHERE lastname='Jones'");
        for (Row row : results) {
            System.out.format("%s %d\n", row.getString("firstname"), row.getInt("age"));
        }

        // Update the same user with a new age
        session.execute("update users set age = 36 where lastname = 'Jones'");

        // Select and show the change
        results = session.execute("select * from users where lastname='Jones'");
        for (Row row : results) {
            System.out.format("%s %d\n", row.getString("firstname"), row.getInt("age"));
        }

        // Delete the user from the users table
        session.execute("DELETE FROM users WHERE lastname = 'Jones'");

        // Show that the user is gone
        results = session.execute("SELECT * FROM users");
        for (Row row : results) {
            System.out.format("%s %d %s %s %s\n", row.getString("lastname"), row.getInt("age"), row.getString("city"),
                    row.getString("email"), row.getString("firstname"));
        }

        // Clean up the connection by closing it
        cluster.close();
    }
}

执行时我收到此错误：

log4j:WARN No appenders could be found for logger (com.datastax.driver.core.SystemProperties).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
Exception in thread "main" com.datastax.driver.core.exceptions.InvalidQueryException: Keyspace 'demo' does not exist
    at com.datastax.driver.core.exceptions.InvalidQueryException.copy(InvalidQueryException.java:35)
    at com.datastax.driver.core.DefaultResultSetFuture.extractCauseFromExecutionException(DefaultResultSetFuture.java:289)
    at com.datastax.driver.core.Cluster.connect(Cluster.java:287)
    at org.sparkexamples.cassandraExample.main.App.main(App.java:17)
Caused by: com.datastax.driver.core.exceptions.InvalidQueryException: Keyspace 'demo' does not exist
    at com.datastax.driver.core.Responses$Error.asException(Responses.java:103)
    at com.datastax.driver.core.DefaultResultSetFuture.onSet(DefaultResultSetFuture.java:140)
    at com.datastax.driver.core.RequestHandler.setFinalResult(RequestHandler.java:293)
    at com.datastax.driver.core.RequestHandler.onSet(RequestHandler.java:455)
    at com.datastax.driver.core.Connection$Dispatcher.messageReceived(Connection.java:734)
    at org.jboss.netty.channel.SimpleChannelUpstreamHandler.handleUpstream(SimpleChannelUpstreamHandler.java:70)
    at org.jboss.netty.handler.timeout.IdleStateAwareChannelUpstreamHandler.handleUpstream(IdleStateAwareChannelUpstreamHandler.java:36)
    at org.jboss.netty.channel.DefaultChannelPipeline.sendUpstream(DefaultChannelPipeline.java:564)
    at org.jboss.netty.channel.DefaultChannelPipeline$DefaultChannelHandlerContext.sendUpstream(DefaultChannelPipeline.java:791)
    at org.jboss.netty.handler.timeout.IdleStateHandler.messageReceived(IdleStateHandler.java:294)
    at org.jboss.netty.channel.SimpleChannelUpstreamHandler.handleUpstream(SimpleChannelUpstreamHandler.java:70)
    at org.jboss.netty.channel.DefaultChannelPipeline.sendUpstream(DefaultChannelPipeline.java:564)
    at org.jboss.netty.channel.DefaultChannelPipeline$DefaultChannelHandlerContext.sendUpstream(DefaultChannelPipeline.java:791)
    at org.jboss.netty.channel.Channels.fireMessageReceived(Channels.java:296)
    at org.jboss.netty.handler.codec.oneone.OneToOneDecoder.handleUpstream(OneToOneDecoder.java:70)
    at org.jboss.netty.channel.DefaultChannelPipeline.sendUpstream(DefaultChannelPipeline.java:564)
    at org.jboss.netty.channel.DefaultChannelPipeline$DefaultChannelHandlerContext.sendUpstream(DefaultChannelPipeline.java:791)
    at org.jboss.netty.channel.Channels.fireMessageReceived(Channels.java:296)
    at org.jboss.netty.handler.codec.frame.FrameDecoder.unfoldAndFireMessageReceived(FrameDecoder.java:462)
    at org.jboss.netty.handler.codec.frame.FrameDecoder.callDecode(FrameDecoder.java:443)
    at org.jboss.netty.handler.codec.frame.FrameDecoder.messageReceived(FrameDecoder.java:303)
    at org.jboss.netty.channel.SimpleChannelUpstreamHandler.handleUpstream(SimpleChannelUpstreamHandler.java:70)
    at org.jboss.netty.channel.DefaultChannelPipeline.sendUpstream(DefaultChannelPipeline.java:564)
    at org.jboss.netty.channel.DefaultChannelPipeline.sendUpstream(DefaultChannelPipeline.java:559)
    at org.jboss.netty.channel.Channels.fireMessageReceived(Channels.java:268)
    at org.jboss.netty.channel.Channels.fireMessageReceived(Channels.java:255)
    at org.jboss.netty.channel.socket.nio.NioWorker.read(NioWorker.java:88)
    at org.jboss.netty.channel.socket.nio.AbstractNioWorker.process(AbstractNioWorker.java:108)
    at org.jboss.netty.channel.socket.nio.AbstractNioSelector.run(AbstractNioSelector.java:318)
    at org.jboss.netty.channel.socket.nio.AbstractNioWorker.run(AbstractNioWorker.java:89)
    at org.jboss.netty.channel.socket.nio.NioWorker.run(NioWorker.java:178)
    at org.jboss.netty.util.ThreadRenamingRunnable.run(ThreadRenamingRunnable.java:108)
    at org.jboss.netty.util.internal.DeadLockProofWorker$1.run(DeadLockProofWorker.java:42)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

另外，我用spark（maven / libs）配置了所有内容，但我不知道如何使用java代码创建密钥空间？

提前感谢。

Answer 1

您已有session个实例。使用它来发出create keyspace命令：

session.execute("CREATE KEYSPACE IF NOT EXISTS  test WITH replication = {"
  + " 'class': 'SimpleStrategy', "
  + " 'replication_factor': '3' "
  + "};" );

IF NOT EXISTS部分将阻止语句在密钥空间已存在的情况下抛出错误。

Answer 2

您可以使用CQL语句CREATE KEYSPACE创建keypsace。有关详细信息，请参阅此文档http://docs.datastax.com/en/cql/3.0/cql/cql_reference/create_keyspace_r.html

从java代码运行SELECT或CREATE语句之间没有区别。

Answer 3

创建keyspace_creation.cql，如下所示：
- ＆GT; vim keyspace_creation.cql

cqlsh> source '~/$CASSANDRA_HOME/bin/keyspace_creation.cql';

- ＆GT; cd $ CASSANDRA_HOME / bin
- ＆GT; ./cqlsh

{{1}}

如何在cassandra中创建键空间？

3 个答案: