libcassandra开发示例

一、前言

libcassandra是Cassandra官方推出的C/C++ API库。与thrift接口（另一个API库）相比，其接口更丰富，对类型匹配更细致。

通过实践，私下也觉得libcassandra比thrift接口更好用。当然这只是个人观点。

有关libcassandra的特点、安装等，在另一篇随笔里已有介绍，本篇把相应代码示例补上。

二、环境

创建keyspace、table如下：

create keyspace hs WITH replication={‘class‘:‘SimpleStrategy‘, ‘replication_factor‘:2};

use hs;

create columnfamily SAMPLE(
  ID        int,
  GID       bigint,
  DATA      blob,
  PRIMARY KEY(ID)
);

三、示例代码

为简便起见，这里只写了Insert和select的示例，update和delete的示例与insert类似。

#include "cassandra.h"
#include <string.h>
#include <stdio.h>

class LibCassDemo
{
private:
     CassFuture     *m_pConnFuture;
     CassCluster    *m_pCluster;
     CassPrepared   *m_pInsertStmt = NULL;
     CassPrepared   *m_pSelectStmt = NULL;
public:
     CassSession    *m_pSession;　　//其实该成员变量也应是私有的，为偷懒改成公共的了

public:
    LibCassDemo() {}
    ~LibCassDemo()
    {
        disconnect();
    }

    //连接Cassandra
    bool connect()
    {
       if (m_bConnect) return true;

       m_pCluster = cass_cluster_new();
       m_pSession = cass_session_new();
       cass_cluster_set_contact_points(m_pCluster, "localhost");
       cass_cluster_set_credentials(m_pCluster, "cassandra", "cassandra");
       m_pConnFuture = cass_session_connect(m_pSession, m_pCluster);
       if (cass_future_error_code(m_pConnFuture)!=CASS_OK)　　//错误处理
       {
          const char* message;
          size_t message_length;
          cass_future_error_message(m_pConnFuture, &message, &message_length);
          fprintf(stderr, "Unable to connect: ‘%.*s‘\n", (int)message_length, message);
          return false;
       }
       printf("Connect Successful!\n");
       m_bConnect = true;
       return m_bConnect;
    }

    //断开Cassandra
    void disconnect()
    {
       if (!m_bConnect) return;
       //关闭session并释放局部变量
       CassFuture *pCloseFuture = cass_session_close(m_pSession);
       cass_future_wait(pCloseFuture);
       cass_future_free(pCloseFuture);
       //释放所有成员变量
       if (m_pInsertStmt) cass_prepared_free(m_pInsertStmt);
       if (m_pSelectStmt) cass_prepared_free(m_pSelectStmt);
       cass_future_free(m_pConnFuture);
       cass_cluster_free(m_pCluster);
       cass_session_free(m_pSession);
       m_bConnect = false;
       printf("Disonnect Successful!\n");
    }

    //相同的INSERT语句只须Prepare一次即可
    CassPrepared * buildInsertStmt()
    {
       string cql;
       if (m_pInsertStmt==NULL)
       {
          cql = "INSERT INTO SAMPLE (ID, GID, DATA) VALUES (?, ?, ?)";
          CassFuture *pPrepareFuture = cass_session_prepare(m_pSession, cql.c_str());
          if (cass_future_error_code(pPrepareFuture)!=CASS_OK)　　//错误处理
          {
             const char* message;
             size_t message_length;
             cass_future_error_message(pPrepareFuture, &message, &message_length);
             fprintf(stderr, "Unable to prepare Insert Statement: ‘%.*s‘\n", (int)message_length, message);
          }
          else
             m_pInsertStmt = (CassPrepared*)cass_future_get_prepared(pPrepareFuture);
          cass_future_free(pPrepareFuture);
       }
       return m_pInsertStmt;
    }

    //同样的，相同的SELECT语句也只须Prepare一次
    CassPrepared * buildSelectStmt()
    {
       string cql;
       if (m_pSelectStmt==NULL)
       {
          cql = "SELECT ID, GID, DATA FROM SAMPLE WHERE ID=? ";

          CassFuture *pPrepareFuture = cass_session_prepare(m_pSession, cql.c_str());
          if (cass_future_error_code(pPrepareFuture)!=CASS_OK)　　//错误处理
          {
             const char* message;
             size_t message_length;
             cass_future_error_message(pPrepareFuture, &message, &message_length);
             fprintf(stderr, "Unable to prepare Select Statement: ‘%.*s‘\n", (int)message_length, message);
          }
          else
             m_pSelectStmt = (CassPrepared*)cass_future_get_prepared(pPrepareFuture);
          cass_future_free(pPrepareFuture);
       }
       return m_pSelectStmt;
    }

　　 //获取int型数据
    int32_t getInt32FromRow(const CassRow *row, const uint16_t index)
    {
       int32_t i32;
       CassValue *value = (CassValue*)cass_row_get_column(row, index);
       cass_value_get_int32(value, &i32);
       return i32;
    }

    //获取bigint型数据
    int64_t getInt64FromRow(const CassRow* row, const uint16_t index)
    {
       int64_t i64;
       CassValue *value = (CassValue*)cass_row_get_column(row, index);
       cass_value_get_int64(value, &i64);
       return i64;
    }

    //获取blob型数据
    CassError getStringFromRow(const CassRow *row, const uint16_t index, UCHAR** data, int32_t &len)
    {
       const cass_byte_t* buf;
       size_t sz;
       CassValue *value = (CassValue*)cass_row_get_column(row, index);
       CassError cer = cass_value_get_bytes(value, &buf, &sz);
       if (cer==CASS_OK)
       {
          *data = (UCHAR *)malloc(sz +1);
          memcpy(*data, buf, sz);
          *(*data+sz+1)=‘\0‘;
          len = (int32_t)sz;
       }
       return cer;
   }

}

int main (int argc, char *argv[])
{
   //初始化
   LibCassDemo *cass = new LibCassDemo();
   cass->connect();
   UCHAR primData[128];
   //Init primData here ...

   //写入数据
   CassPrepared *prepared = cass->buildInsertStmt();
   CassBatch *batch = cass_batch_new(CASS_BATCH_TYPE_LOGGED);　　//批量方式
   for (int i=0; i<10; i++)
   {
      CassStatement * stmt = cass_prepared_bind(prepared);
      cass_statement_set_consistency(stmt, CASS_CONSISTENCY_QUORUM);
      cass_statement_bind_int32(stmt, 0, i);　　//第一个是0
      cass_statement_bind_int64(stmt, 1, (i<<8 + i));
      cass_statement_bind_bytes(stmt, 2, primData, 128);
      cass_batch_add_statement(batch, stmt);
      cass_statement_free(stmt);
   }
     CassFuture *batchFuture = cass_session_execute_batch(cass->m_pSession, batch);
     if (cass_future_error_code(batchFuture)!=CASS_OK)　　//错误处理
     {
        const char* message;
        size_t message_length;
        cass_future_error_message(batchFuture, &message, &message_length);
        fprintf(stderr, "Unable to execute BATCH: ‘%.*s‘\n", (int)message_length, message);
     }
     cass_future_free(batchFuture);
     cass_batch_free(batch);

   //读取数据
   prepared = cass->buildSelectStmt();
   stmt = cass_prepared_bind(prepared);
   int id=7;
   cass_statement_bind_int32(stmt, 0, id);
   CassFuture *readFuture = cass_session_execute(cass->m_pSession, stmt);
   CassResult *result = (CassResult*)cass_future_get_result(readFuture);　　//从CassFuture获取查询结果
   CassIterator *iter = cass_iterator_from_result(result);　　//转换为CassIterator
   while(cass_iterator_next(iter))
   {
      CassRow *row = (CassRow*)cass_iterator_get_row(iter);　　//CassRow和CassError对象无须释放
      printf("ID=%d, GID=%ld, ", cass->getInt32FromRow(row, 0), cass->getInt64FromRow(row, 1));
      UCHAR *pData = (UCHAR *)malloc(128);
      int len;
      cass->getStringFromRow(row, 2, &pData, len);
      printf("DATA is :%s\n", pData);
      free(pData);
   }
   cass_iterator_free(iter);
   cass_result_free(result);
   cass_future_free(readFuture);
   cass_statement_free(stmt);

   //释放资源
   delete cass;
}