对libpq进行简单的c++封装

　　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：

 1 #ifndef _DBCONN_HPP_
 2 #define _DBCONN_HPP_
 3 
 4 #include <iostream>
 5 #include <string>
 6 #include <libpq-fe.h>
 7 #include <map>
 8 using namespace std;
 9 
10 typedef map<int,map<string,string> > map_result;
11 
12 class Conn
13 {
14 public:
15     Conn(char *connstring);
16     ~Conn();
17     map_result Fetch(char *SQL);
18     int Exec(char *SQL);
19 private:
20     void FinishConnection(PGconn *conn);
21     void Reset();
22 private:
23     PGconn *_conn;
24     const char *_conninfo;
25     PGresult *_res;
26 };
27 
28 
29 #endif // _DBCONN_HPP_

　　

  1 #include "DBConn.h"
  2 
  3 Conn::Conn(char *connstring)
  4 {
  5     _conninfo = connstring;
  6     _conn = PQconnectdb(_conninfo);
  7     if (PQstatus(_conn) != CONNECTION_OK)
  8     {
  9         fprintf(stderr, "Could not connect to db/n%s", PQerrorMessage(_conn));
 10         FinishConnection(_conn);
 11     }
 12 }
 13 Conn::~Conn()
 14 {
 15     _conninfo = NULL;
 16     FinishConnection(_conn);
 17 }
 18 void Conn::Reset()
 19 {  
 20     PQfinish(_conn);
 21     _conn = PQconnectdb(_conninfo);
 22 }
 23 
 24 void Conn::FinishConnection(PGconn *conn)
 25 {  
 26     PQfinish(_conn);
 27 }
 28  
 29 map_result Conn::Fetch(char *SQL)
 30 {  
 31     int row, col;
 32     map_result results;
 33     map<string,string> pairs;
 34     // 检查连接
 35     if (PQstatus(_conn) != CONNECTION_OK)
 36     {
 37         this->Reset();
 38     }
 39     // 开始一个事物 
 40     _res = PQexec(_conn, "BEGIN");
 41     if (PQresultStatus(_res) != PGRES_COMMAND_OK)
 42     {
 43         fprintf(stderr, "Failed to BEGIN transaction /n%s", PQerrorMessage(_conn));
 44         PQclear(_res);
 45         FinishConnection(_conn);
 46     }
 47     // 建立游标 
 48     string FinalSQL = string("DECLARE myportal CURSOR FOR ") +  
 49                       string(SQL);
 50     _res = PQexec(_conn,FinalSQL.c_str());
 51     if (PQresultStatus(_res) != PGRES_COMMAND_OK)
 52     {  
 53         fprintf(stderr, "QUERY FAILED/n%s/n", PQerrorMessage(_conn));
 54         PQclear(_res);
 55         FinishConnection(_conn);
 56     }
 57     PQclear(_res);
 58  
 59     _res = PQexec(_conn, "FETCH ALL in myportal");
 60     if (PQresultStatus(_res) != PGRES_TUPLES_OK)
 61     {
 62         fprintf(stderr, "FETCH ALL failed/n%s/n", PQerrorMessage(_conn));
 63         PQclear(_res);
 64         FinishConnection(_conn);
 65     }
 66     else  
 67     {
 68         for (row=0;row<PQntuples(_res);row++)
 69         {
 70             for(col=0;col<PQnfields(_res);col++)
 71             {
 72                 pairs[PQfname(_res,col)] = PQgetvalue(_res, row, col);
 73             }
 74             results[row] = pairs;
 75         }
 76     }
 77     // 结束一个事物 
 78     _res = PQexec(_conn, "END");
 79     if (PQresultStatus(_res) != PGRES_COMMAND_OK)
 80     {
 81         fprintf(stderr, "Failed to END transaction /n%s", PQerrorMessage(_conn));
 82         PQclear(_res);
 83         FinishConnection(_conn);
 84     }
 85     return results;
 86 }
 87 int Conn::Exec(char *sql)
 88 {
 89     // 检查连接
 90     if (PQstatus(_conn) != CONNECTION_OK)
 91     {
 92         this->Reset();
 93     }
 94     // 开始一个事物
 95     _res = PQexec(_conn, "BEGIN");
 96     if (PQresultStatus(_res) != PGRES_COMMAND_OK)
 97     {
 98         fprintf(stderr, "Failed to BEGIN transaction /n%s/n", PQerrorMessage(_conn));
 99         PQclear(_res);
100         FinishConnection(_conn);
101     }
102     // 执行插入
103     _res = PQexec(_conn, sql);
104     if (PQresultStatus(_res) != PGRES_COMMAND_OK)
105     {
106         fprintf(stderr, "Failed to execute INSERT /n%s/n", PQerrorMessage(_conn));
107         PQclear(_res);
108         FinishConnection(_conn);
109     }
110     // 提交事物
111     _res = PQexec(_conn, "COMMIT");
112     if (PQresultStatus(_res) != PGRES_COMMAND_OK) 
113     {
114         fprintf(stderr, "Failed to COMMIT transaction/n%s/n", PQerrorMessage(_conn));
115         PQclear(_res);
116         FinishConnection(_conn);
117     }
118     // 结束一个事物 
119     _res = PQexec(_conn, "END");
120     if (PQresultStatus(_res) != PGRES_COMMAND_OK)
121     {
122         fprintf(stderr, "Failed to END transaction /n%s", PQerrorMessage(_conn));
123         PQclear(_res);
124         FinishConnection(_conn);
125     }
126     return 0;
127 }

　　

 1 #include <iostream>    
 2 #include "DBConn.h"  
 3 using namespace std;  
 4   
 5 int main()
 6 {  
 7     map_result res;  
 8     Conn *postgres = new Conn("host=192.168.150.131 dbname=postgres user=enterprisedb password=mayong port=5432 connect_timeout=5");  
 9     for( int i=0; i<4; ++i )  
10     {   
11         postgres->Exec("insert into test (select nextval('s_id'), 'dog', 3)");  
12     }
13     res = postgres->Fetch("SELECT * FROM test where name = 'dog'");  
14     map_result::iterator it = res.begin();  
15     for( ; it!=res.end(); ++it )  
16     {  
17         cout << "ROW:" << it->first << endl;  
18         map<string,string>::iterator itField = it->second.begin();  
19         for( ; itField!=it->second.end(); ++itField )  
20         {  
21             cout << "Field:" << itField->first << "  Value:" << itField->second << endl;  
22         }  
23     }
24     
25     postgres->Exec("update test set name = 'cat' where name = 'dog'");
26     cout << "--------------------------------" << endl;
27     res = postgres->Fetch("SELECT * FROM test where name = 'cat'");  
28     it = res.begin();  
29     for( ; it!=res.end(); ++it )  
30     {  
31         cout << "ROW:" << it->first << endl;  
32         map<string,string>::iterator itField = it->second.begin();  
33         for( ; itField!=it->second.end(); ++itField )  
34         {  
35             cout << "Field:" << itField->first << "  Value:" << itField->second << endl;  
36         }  
37     }  
38     
39     postgres->Exec("delete from test where name = 'cat'");  
40     
41     delete postgres;
42     return 0;  
43 }

运行结果如下：

ROW:0

Field:age  Value:3

Field:id  Value:243

Field:name  Value:dog

ROW:1

Field:age  Value:3

Field:id  Value:244

Field:name  Value:dog

ROW:2

Field:age  Value:3

Field:id  Value:245

Field:name  Value:dog

ROW:3

Field:age  Value:3

Field:id  Value:246

Field:name  Value:dog

--------------------------------

ROW:0

Field:age  Value:3

Field:id  Value:243

Field:name  Value:cat

ROW:1

Field:age  Value:3

Field:id  Value:244

Field:name  Value:cat

ROW:2

Field:age  Value:3

Field:id  Value:245

Field:name  Value:cat

ROW:3

Field:age  Value:3

Field:id  Value:246

Field:name  Value:cat