[poco] 访问数据库
From: https://blog.csdn.net/hl2015222050145/article/details/52335422?utm_source=blogxgwz6
poco访问数据基本步骤：
a. 创建会话(session)
b. 从DB中读写数据
c. 使用statements
d. 使用容器（Collection） (数据，集合...)
e. 使用limit限定
f. 如何使用复杂的数据类型(如何将一个C++对象映射到数据库的表
创建会话：Session create(const std::string& connectorKey, const std::string& connectionString);
参数1：SQLite；MySQL；或者ODBC，ODBC支持Oracle, SQLite, DB2, SQLServer和PostgreSQL。
参数2：就是数据库文件的路径或者连接字符
基本操作（增删查改）：
增：
std::string aName("Peter");
ses << "INSERT INTO 表名 VALUES(" << aName << ")", now;
或者ses << "INSERT INTO 表名 VALUES(?)", use(aName), now;
查：
一般查找
std::string aName;
ses << "SELECT NAME FROM FORENAME", into(aName), now; // aName的默认值为空字符串
ses << "SELECT NAME FROM FORENAME", into(aName, "default"), now;
匹配查找 先into后use 且不能使用常量 如:4
std::string aName;
std::string match("Peter")
ses << "SELECT NAME FROM FORENAME WHERE NAME=?", into(aName), use(match), now;
poco_assert (aName == match);
多字节匹配查找
std::string firstName("Peter";
std::string lastName("Junior");
int age = 0;
ses << "INSERT INTO PERSON VALUES (?, ?, ?)", use(firstName), use(lastName), use(age), now;
ses << "SELECT (firstname, lastname, age) FROM Person", into(firstName), into(lastName), into(age), now;
into语句允许定义一个默认值,主要针对数据库查询里面包含空时候
ses << "SELECT (firstname, lastname, age) FROM Person", into(firstName), into(lastName), into(age, -1), now;
改：
session << "update Person set Address = ? WHERE Name= ?", use(addr),use(name),now;
使用Statements：
用于保存SQl语句，使得多次查询。
std::string aName("Peter");
Statement stmt = ( ses << "INSERT INTO FORENAME VALUES(?)", use(aName) );//括号必须
或者
Statement stmt(ses);
stmt << "INSERT INTO FORENAME VALUES(?)", use(aName);
eg：
std::string aName("Peter");
Statement stmt = ( ses << "INSERT INTO FORENAME VALUES(?)", use(aName) );
.
.
stmt.execute();
poco_assert (stmt.done());
容器使用：
默认支持以下容器类：
a. vector(数组): 无特别要求
b. set: 类型需要支持<操作符，注意：重复的key/value将忽略
c. multiset: 需支持<操作符
d. map: 需支持()操作符，并且按key返回对象，注意：重复的key/value将忽略
e. multimap: 需支持()操作符，并按key返加对象.
std::vector
ses << "SELECT NAME FROM FORENAME", into(names), now;
Limit限定：针对查询结果的个数限定
std::vector
ses << "SELECT NAME FROM FORENAME", into(names), limit(50), now;
以上代码将只返回50行的数据。（当然也可能什么都不返回）,并追加到 names这个容量中。如果想确保50行记录返回，需要设置limit的第二参数为true(默认为false):
std::vector
ses << "SELECT NAME FROM FORENAME", into(names), limit(50, true), now;
Statement stmt = (ses << "SELECT NAME FROM FORENAME", into(aName), lowerLimit(1), upperLimit(10));//限制范围
Statement stmt = (ses << "SELECT NAME FROM FORENAME", into(aName), range(1,10));
类作为保存变量：这个就是将自定义类作为容器查询
namespace Poco
{
namespace Data
{
template <>
class TypeHandler
{
.....
}
}
}
记录集(RecordSet)
a. 遍历数据表中所有的行与列
b. 获取各列的元信息，比如名称，类型，长度等.
Statement select(session);
select << "SELECT * FROM Person";
select.execute();
RecordSet rs(select);
遍历结果：
bool more = rs.moveFirst();
while (more)
{
for (std::size_t col = 0; col < cols; ++col)
{
std::cout << rs[col].convert
}
std::cout << std::endl;
more = rs.moveNext();
}
Tuples：在数据库中的列类型已知的情阅下，Poco::Tuple以及Tuple数组提供了更简便的方法获取数据。
typedef Poco::Tuple
typedef std::vector
People people;
people.push_back(Person("Bart Simpson", "Springfield", 12));
people.push_back(Person("Lisa Simpson", "Springfield", 10));
Statement insert(session);
insert << "INSERT INTO Person VALUES(?, ?, ?)",
use(people), now;
当然，tuple也可以用于查询:
Statement select(session);
select << "SELECT Name, Address, Age FROM Person", into(people), now;
for (People::const_iterator it = people.begin(); it != people.end(); ++it)
{
std::cout << "Name: " << it->get<0>() <<
", Address: " << it->get<1>() <<
", Age: " << it->get<2>() <
参考链接：http://pocoproject.org/docs/00200-DataUserManual.html
测试代码：
#include "Poco/Data/Session.h"
#include "Poco/Data/MySQL/Connector.h"
#include
#include
using namespace Poco::Data::Keywords;
using Poco::Data::Session;
using Poco::Data::Statement;
struct Person
{
std::string name;
std::string address;
int age;
};
int main(int argc, char** argv)
{
Poco::Data::MySQL::Connector::registerConnector();
// 创建 session
Session session("MySQL", "host=127.0.0.1;port=3306;db=demo;user=admin;password=admin;compress=true;auto-reconnect=true");
// 删除已存在的表
session << "DROP TABLE IF EXISTS Person", now;
// 创建新表
session << "CREATE TABLE Person (Name char(20),Address char(30) ,Age integer)", now;//varchar 会报错
// 插入数据
Person person =
{
"Bart Simpson",
"Springfield",
12
};
Statement insert(session);
insert << "INSERT INTO Person VALUES(?, ?, ?)",
use(person.name),
use(person.address),
use(person.age);
insert.execute();
person.name = "Lisa Simpson";
person.address = "Springfield";
person.age = 10;
insert.execute();
//查询数据
Statement select(session);
select << "select Name, Address, Age FROM Person",
into(person.name),
into(person.address),
into(person.age),
range(0, 1); // 只查询前两行
while (!select.done())
{
select.execute();
std::cout << person.name << " " << person.address << " " << person.age << std::endl;
}
std::string addr = "hubeilichuan";
std::string name = "Lisa Simpson";
session << "update Person set Address = ? WHERE Name= ?", use(addr),use(name),now;
// 另一种查询方式
std::vector
session << "SELECT Address FROM Person",
into(names),
now;
for (std::vector
{
std::cout << *it << std::endl;
}
getchar();
return 0;
}
测试工程链接：http://download.csdn.net/detail/hl2015222050145/9614574
编译好的动态库链接：http://download.csdn.net/detail/hl2015222050145/9614205