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Mybatis-基础使用

来源：SegmentFault 2023-02-18 16:14:23 0浏览收藏

来到golang学习网的大家，相信都是编程学习爱好者，希望在这里学习数据库相关编程知识。下面本篇文章就来带大家聊聊《Mybatis-基础使用》，介绍一下MySQL、数据库、jdbc、mybatis、pgsql，希望对大家的知识积累有所帮助，助力实战开发！

Class.forName("com.mysql.jdbc.Driver");

2. 获取数据库连接

然后需要获取数据库连接，如下所示。

// url用于标识数据库位置，即告诉Jdbc连接哪个数据库
String url = "jdbc:mysql://127.0.0.1:3306/test";
// 数据库用户名和密码
String username = "root";
String password = "root";
// Connection是数据库编程中的一个重要对象，客户端与数据库的所有交互均依赖该对象
Connection connection = DriverManager.getConnection(url, username, password);

Statement statement = connection.createStatement();

Statement statement = connection.createStatement();
String sql = "SELECT * FROM worker";
ResultSet resultSet = statement.executeQuery(sql);

由于

String sql = "SELECT * FROM worker WHERE sex = ?"
// 获取PreparedStatement对象时就需要传入SQL语句进行预编译
PreparedStatement preparedStatement = connection.prepareStatement(sql);
// 设置参数，将第一个占位符替换为"male"
preparedStatement.setString(1, "male");
// 执行查询，查询结果由ResultSet对象封装
ResultSet resultSet = preparedStatement.executeQuery();

相较于

if (resultSet != null) {
    resultSet.close();
}
if (preparedStatement != null) {
    preparedStatement.close();
}
if (connection != null) {
    connection.close();
}

二. Mybatis基础使用

1. Mybatis结构

<?xml version="1.0" encoding="UTF-8" ?><mapper namespace="MyMapper"><select id="selectWorker" parametertype="java.lang.String" resulttype="com.test.po.Worker">
        SELECT * FROM worker WHERE sex = #{sex}
    </select></mapper>

原始

// 指定全局配置文件
String resource = "mybatis-config.xml";
// 读取全局配置文件
InputStream inputStream = Resources.getResourceAsStream(resource);
// 构建SqlSessionFactory
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
// 获取SqlSession
SqlSession sqlSession = sqlSessionFactory.openSession();

// 第一个参数为：（映射文件的）命名空间 + "." + （映射文件的SQL语句的）id
// 第二个参数为：需要执行的SQL语句的参数值
List<worker> workers = sqlSession.selectList("MyMapper.selectWorker", "male");</worker>

最后不要忘记关闭

if (sqlSession != null) {
    sqlSession.close();
}

3. 动态代理Mybatis使用

动态代理

<mapper namespace="com.test.mapper.WorkerMapper"><select id="selectWorkerBySex" parametertype="java.lang.String" resulttype="com.test.po.Worker">
        SELECT * FROM worker WHERE sex = #{sex}
    </select></mapper>

上面的映射文件中，

public interface WorkerMapper {

    List<worker> selectWorkerBySex(String sex);

}</worker>

动态代理

// 指定全局配置文件
String resource = "mybatis-config.xml";
// 读取全局配置文件
InputStream inputStream = Resources.getResourceAsStream(resource);
// 构建SqlSessionFactory
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
// 获取SqlSession
SqlSession sqlSession = sqlSessionFactory.openSession();

获取映射接口的实例的步骤如下所示。

WorkerMapper workerMapper = sqlSession.getMapper(WorkerMapper.class);

获取映射接口的实例后，通过调用映射接口的实例的方法来执行

List<worker> list = workerMapper.selectWorkerBySex("male");</worker>

最后关闭

if (sqlSession != null) {
    sqlSession.close();
}

三. Mybatis标签语法

本节对映射文件中的常用标签进行分析，无特殊说明时，默认

<?xml version="1.0" encoding="UTF-8" ?><mapper namespace="com.test.mapper.WorkerMapper"><select id="selectAgeSalaryByMap" parametertype="java.util.Map" resulttype="com.test.po.Worker">
        SELECT * FROM worker WHERE age > #{age} and salary > #{salary}
    </select></mapper>

映射接口如下所示。

public interface WorkerMapper {

    List<worker> selectAgeSalaryByMap(Map<string long> map);

}</string></worker>

测试代码如下所示（省略

......
WorkerMapper workerMapper = sqlSession.getMapper(WorkerMapper.class);
Map<string long> map = new HashMap();
map.put("age", 20L);
map.put("salary", 10000L);
List<worker> workers = workerMapper.selectAgeSalaryByMap(map);
......</worker></string>

例子2：通过

public class SelectInfo {

    private Long age;
    private Long salary;

    public Long getAge() {
        return age;
    }

    public void setAge(Long age) {
        this.age = age;
    }

    public Long getSalary() {
        return salary;
    }

    public void setSalary(Long salary) {
        this.salary = salary;
    }
    
}

映射文件如下所示。

<?xml version="1.0" encoding="UTF-8" ?><mapper namespace="com.test.mapper.WorkerMapper"><select id="selectAgeSalaryByBean" parametertype="com.test.po.SelectInfo" resulttype="com.test.po.Worker">
        SELECT * FROM worker WHERE age > #{age} and salary > #{salary}
    </select></mapper>

映射接口如下所示。

public interface WorkerMapper {

    List<worker> selectAgeSalaryByBean(SelectInfo selectInfo);

}</worker>

测试代码如下所示（省略

......
WorkerMapper workerMapper = sqlSession.getMapper(WorkerMapper.class);
SelectInfo selectInfo = new SelectInfo();
selectInfo.setAge(20L);
selectInfo.setSalary(10000L);
List<worker> workers = workerMapper.selectAgeSalaryByBean(selectInfo);
......</worker>

2. 标签

<?xml version="1.0" encoding="UTF-8" ?><mapper namespace="com.test.mapper.WorkerMapper"><insert id="insertWorker" parametertype="com.test.po.Worker" keyproperty="id" usegeneratedkeys="true">
        INSERT INTO
        worker (name, sex, age, salary)
        VALUES
        (#{name}, #{sex}, #{age}, #{salary})
    </insert></mapper>

映射接口如下所示。

public interface WorkerMapper {

    Integer insertWorker(Worker worker);

}

public class Worker {

    private long id;
    private String name;
    private String sex;
    private long age;
    private long salary;

    public Worker() {}

    public Worker(String name, String sex,
                  long age, long salary) {
        this.name = name;
        this.sex = sex;
        this.age = age;
        this.salary = salary;
    }

    // 省略getter和setter
    ......

}

worker表的创建语句如下。

CREATE TABLE worker(
    id INT(11) PRIMARY KEY NOT NULL AUTO_INCREMENT,
    name VARCHAR(30) NOT NULL,
    sex VARCHAR(30) NOT NULL,
    age INT(11) NOT NULL,
    salary INT(11) NOT NULL
)

测试代码如下所示（省略

...
WorkerMapper workerMapper = sqlSession.getMapper(WorkerMapper.class);
Worker worker = new Worker("Lee", "male", 20L, 10000L);
Integer result = workerMapper.insertWorker(worker);
System.out.println(result + " pieces of data were inserted.");
System.out.println("The primary key of the inserted data is " + worker.getId());
...

3. 和标签

这两个标签的属性与

CREATE TABLE book(
    id INT(11) PRIMARY KEY AUTO_INCREMENT,
    b_name VARCHAR(255) NOT NULL,
    b_price INT(11) NOT NULL
)

创建一个

public class Book {

    private long id;
    private String bookName;
    private long bookPrice;

    // 省略getter和setter
    ......

}

可以看到，

<?xml version="1.0" encoding="UTF-8" ?><mapper namespace="com.test.mapper.BookMapper"><resultmap id="bookResultMap" type="com.test.po.Book"><result column="id" property="id"></result><result column="b_name" property="bookName"></result><result column="b_price" property="bookPrice"></result></resultmap><select id="selectBookByName" parametertype="java.lang.String" resultmap="bookResultMap">
        SELECT * FROM book WHERE b_name=#{bookName}
    </select></mapper>

public interface BookMapper {

    List<book> selectBookByName(String bookName);

}</book>

测试代码如下所示（省略

......
BookMapper bookMapper = sqlSession.getMapper(BookMapper.class);
List<book> mathBooks = bookMapper.selectBookByName("Math");
......</book>

如果

public class Book {

    private long id;
    private String bookName;
    private long bookPrice;

    private BookStore bookStore;

    // 省略getter和setter
    ......

}

public class BookStore {

    private long bsId;
    private String bsName;

    // 省略getter和setter
    ......

}

此时映射文件如下所示。

<?xml version="1.0" encoding="UTF-8" ?><mapper namespace="com.test.mapper.BookMapper"><resultmap id="bookResultMap" type="com.test.po.Book"><result column="id" property="id"></result><result column="b_name" property="bookName"></result><result column="b_price" property="bookPrice"></result><association property="bookStore" javatype="com.test.po.BookStore"><result column="bs_id" property="bsId"></result><result column="bs_name" property="bsName"></result></association></resultmap><select id="selectBookByName" parametertype="java.lang.String" resultmap="bookResultMap">
        SELECT * FROM book WHERE b_name=#{bookName}
    </select></mapper>

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