对libpq进行简单的c++封装

最新推荐文章于 2025-01-06 15:11:19 发布

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最新推荐文章于 2025-01-06 15:11:19 发布

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文章标签： c++ command iterator string postgresql sql

本文链接：https://blog.youkuaiyun.com/osyun/article/details/6662326

最近项目需要用c++操作PostgreSQL，编译c++的libpqxx遇到太多问题，虽然搞定，但不适合项目开发和维护。且官网似乎对此第三方库并不推荐，所以就查阅了相关资料，封装了一个c++的hpp，用来操作数据库。代码如下：

DBConn.h

#ifndef _DBCONN_HPP_
#define _DBCONN_HPP_

#include <iostream>
#include <string>
#include <libpq-fe.h>
#include <map>
using namespace std;

typedef map<int,map<string,string> > map_result;

class Conn
{
public:
    Conn(char *connstring);
    ~Conn();
    map_result Fetch(char *SQL);
    int Exec(char *SQL);
private:
void FinishConnection(PGconn *conn);
void Reset();
private:
    PGconn *_conn;
    const char *_conninfo;
    PGresult *_res;
};

#endif // _DBCONN_HPP_

DBConn.cpp

#include "DBConn.h"

Conn::Conn(char *connstring)
{
_conninfo = connstring;
    _conn = PQconnectdb(_conninfo);
    if (PQstatus(_conn) != CONNECTION_OK)
    {
        fprintf(stderr, "Could not connect to db/n%s", PQerrorMessage(_conn));
        FinishConnection(_conn);
    }
}
Conn::~Conn()
{
_conninfo = NULL;
    FinishConnection(_conn);
}
void Conn::Reset()
{
    PQfinish(_conn);
    _conn = PQconnectdb(_conninfo);
}

void Conn::FinishConnection(PGconn *conn)
{
    PQfinish(_conn);
}

map_result Conn::Fetch(char *SQL)
{
    int row, col;
    map_result results;
    map<string,string> pairs;
    // 检查连接
    if (PQstatus(_conn) != CONNECTION_OK)
    {
        this->Reset();
    }
    // 开始一个事物
    _res = PQexec(_conn, "BEGIN");
    if (PQresultStatus(_res) != PGRES_COMMAND_OK)
    {
        fprintf(stderr, "Failed to BEGIN transaction /n%s", PQerrorMessage(_conn));
        PQclear(_res);
        FinishConnection(_conn);
    }
    // 建立游标
    string FinalSQL = string("DECLARE myportal CURSOR FOR ") +
                      string(SQL);
    _res = PQexec(_conn,FinalSQL.c_str());
    if (PQresultStatus(_res) != PGRES_COMMAND_OK)
    {
        fprintf(stderr, "QUERY FAILED/n%s/n", PQerrorMessage(_conn));
        PQclear(_res);
        FinishConnection(_conn);
    }
    PQclear(_res);

    _res = PQexec(_conn, "FETCH ALL in myportal");
    if (PQresultStatus(_res) != PGRES_TUPLES_OK)
    {
        fprintf(stderr, "FETCH ALL failed/n%s/n", PQerrorMessage(_conn));
        PQclear(_res);
        FinishConnection(_conn);
    }
    else
    {
        for (row=0;row<PQntuples(_res);row++)
        {
            for(col=0;col<PQnfields(_res);col++)
            {
                pairs[PQfname(_res,col)] = PQgetvalue(_res, row, col);
            }
            results[row] = pairs;
        }
    }
    // 结束一个事物
    _res = PQexec(_conn, "END");
    if (PQresultStatus(_res) != PGRES_COMMAND_OK)
    {
        fprintf(stderr, "Failed to END transaction /n%s", PQerrorMessage(_conn));
        PQclear(_res);
        FinishConnection(_conn);
    }
    return results;
}
int Conn::Exec(char *sql)
{
    // 检查连接
    if (PQstatus(_conn) != CONNECTION_OK)
    {
        this->Reset();
    }
    // 开始一个事物
    _res = PQexec(_conn, "BEGIN");
    if (PQresultStatus(_res) != PGRES_COMMAND_OK)
    {
        fprintf(stderr, "Failed to BEGIN transaction /n%s/n", PQerrorMessage(_conn));
        PQclear(_res);
        FinishConnection(_conn);
    }
    // 执行插入
    _res = PQexec(_conn, sql);
    if (PQresultStatus(_res) != PGRES_COMMAND_OK)
    {
        fprintf(stderr, "Failed to execute INSERT /n%s/n", PQerrorMessage(_conn));
        PQclear(_res);
        FinishConnection(_conn);
    }
    // 提交事物
    _res = PQexec(_conn, "COMMIT");
    if (PQresultStatus(_res) != PGRES_COMMAND_OK)
    {
        fprintf(stderr, "Failed to COMMIT transaction/n%s/n", PQerrorMessage(_conn));
        PQclear(_res);
        FinishConnection(_conn);
    }
    // 结束一个事物
    _res = PQexec(_conn, "END");
    if (PQresultStatus(_res) != PGRES_COMMAND_OK)
    {
        fprintf(stderr, "Failed to END transaction /n%s", PQerrorMessage(_conn));
        PQclear(_res);
        FinishConnection(_conn);
    }
    return 0;
}

main.cpp

#include <iostream>
#include "DBConn.h"
using namespace std;

int main()
{
    map_result res;
    Conn *postgres = new Conn("host=192.168.150.131 dbname=postgres user=enterprisedb password=mayong port=5432 connect_timeout=5");
    for( int i=0; i<4; ++i )
    {
        postgres->Exec("insert into test (select nextval('s_id'), 'dog', 3)");
    }
    res = postgres->Fetch("SELECT * FROM test where name = 'dog'");
    map_result::iterator it = res.begin();
    for( ; it!=res.end(); ++it )
    {
        cout << "ROW:" << it->first << endl;
        map<string,string>::iterator itField = it->second.begin();
        for( ; itField!=it->second.end(); ++itField )
        {
            cout << "Field:" << itField->first << " Value:" << itField->second << endl;
        }
    }

    postgres->Exec("update test set name = 'cat' where name = 'dog'");
    cout << "--------------------------------" << endl;
    res = postgres->Fetch("SELECT * FROM test where name = 'cat'");
    it = res.begin();
    for( ; it!=res.end(); ++it )
    {
        cout << "ROW:" << it->first << endl;
        map<string,string>::iterator itField = it->second.begin();
        for( ; itField!=it->second.end(); ++itField )
        {
            cout << "Field:" << itField->first << " Value:" << itField->second << endl;
        }
    }

    postgres->Exec("delete from test where name = 'cat'");

    delete postgres;
    return 0;
}