MyBatis一对一实现延迟加载

数据库表


添加外键

在IDEA中创建maven项目

整体架构

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.uek</groupId>
    <artifactId>mybatis04-study01-oneToone-lazyLoad</artifactId>
    <version>1.0-SNAPSHOT</version>


    <!--打包方式-->
    <packaging>jar</packaging>

    <dependencies>
        <!--导入MyBatis的坐标-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.5</version>
        </dependency>
        <!--导入MySQL-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.46</version>
        </dependency>

        <!--日志-->
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>

        <!--单元测试-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.10</version>
        </dependency>

    </dependencies>
</project>

MyBatis的主配置文件

在resource目录下------SqlMapConfig.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>

    <!--配置参数-->
    <settings>
        <!--开启MyBatis支持延迟加载-->
        <setting name="lazyLoadingEnabled" value="true"/>
        <setting name="aggressiveLazyLoading" value="false"/>
    </settings>

    <!--使用typeAliases配置别名，它只能配置到domian中类的别名-->
    <typeAliases>
        <package name="com.uek.domian"/>
    </typeAliases>
    
    <!--配置环境-->
    <environments default="mysql">
        <!--配置mysql的环境-->
        <environment id="mysql">
            <!--配置事务-->
            <transactionManager type="JDBC"></transactionManager>
            <!--配置连接池-->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useUnicode=true&amp;characterEncoding=utf-8&amp;useSSL=false"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
    <!--配置映射文件的位置-->
    <mappers>
        <package name="com.uek.dao"/>
    </mappers>
</configuration>

实体类

public class Account implements Serializable {

    private Integer id;
    private Integer uid;
    private Double money;
    
    //从表实体类应该包含一个主表实体对象的引用
    private User user;

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public Integer getUid() {
        return uid;
    }

    public void setUid(Integer uid) {
        this.uid = uid;
    }

    public Double getMoney() {
        return money;
    }

    public void setMoney(Double money) {
        this.money = money;
    }

    @Override
    public String toString() {
        return "Account{" +
                "id=" + id +
                ", uid=" + uid +
                ", money=" + money +
                '}';
    }
}

public class User implements Serializable {

    private Integer id;
    private String username;
    private String address;
    private String sex;
    private Date birthday;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUsername(String mybatis_saveuser) {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", address='" + address + '\'' +
                ", sex='" + sex + '\'' +
                ", birthday=" + birthday +
                '}';
    }
}

dao层接口

public interface IAccountDao {

    //查询所有账户,并且带有用户名称和地址信息
    List<Account> findAll();


}

public interface IUserDao {

    //查询所有用户
    List<User> findAll();

    //根据id查询用户信息
    User findById(Integer userId);

}

接口配置 IUserDao.xml

注意：在resource目录下新建包时一级一级的建立
必须和dao层的接口的包名一致

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.uek.dao.IAccountDao">
    
    <!--定义封装account和user的resultMap-->
    <resultMap id="accountUserMap" type="account">
        <!--account的数据封装完成   aid是sql语句中起的别名-->
        <id property="id" column="id"></id>
        <result property="uid" column="uid"></result>
        <result property="money" column="money"></result>

        <!--一对一关系映射模型：延迟加载
          select属性指定的内容：查询用户的唯一标识
          column属性指定的内容：用户根据id查询时，所需要的参数的值
        -->
        <association property="user" column="uid" javaType="user" select="com.uek.dao.IUserDao.findById"></association>
    </resultMap>

    <!--查询所有账户-->
    <select id="findAll" resultMap="accountUserMap">
        select * from account
    </select>
</mapper>

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.uek.dao.IUserDao">

    <!--定义User的resultMap-->
    <resultMap id="userAccountMap" type="user">
        <id property="id" column="id"></id>
        <result property="username" column="username"></result>
        <result property="address" column="address"></result>
        <result property="sex" column="sex"></result>
        <result property="birthday" column="birthday"></result>
        <!--配置user对象中的accounts集合的映射-->
        <collection property="accounts" ofType="account">
            <id column="aid" property="id"></id>
            <result property="uid" column="uid"></result>
            <result property="money" column="money"></result>
        </collection>
    </resultMap>

    <!--查询所有方法-->
    <select id="findAll" resultMap="userAccountMap">
        select * from user left outer join account a on u.id = a.uid
    </select>

    <!--根据id查询用户-->
    <select id="findById" parameterType="INT" resultType="user">
        select * from user where id = #{id}
    </select>


</mapper>

测试类

public class AccountTest {

    private InputStream in;
    private SqlSession sqlSession;
    private IAccountDao accountDao;

    @Before   //用于在测试方法执行之前执行
    public void init() throws Exception {
        //1.读取配置文件，生成字节输入流
        in = Resources.getResourceAsStream("SqlMapConfig.xml");
        //2.获取SqlSession对象
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);
        //3.获取SqlSession对象
        sqlSession = factory.openSession();
        //4.获取dao的代理对象
        accountDao = sqlSession.getMapper(IAccountDao.class);
    }


    @After //用于在测试方法执行之后执行
    public void destroy() throws Exception {
        //提交事务
        sqlSession.commit();

        //6.释放资源
        sqlSession.close();
        in.close();
    }

    //第一种方法
    //查询所有账户,同时包含用户名称和地址信息
    @Test
    public void testFindAll(){
        List<Account> accounts = accountDao.findAll();
        for (Account account : accounts) {
            System.out.println("----每个account的信息----");
            System.out.println(account);
            System.out.println(account.getUser());
        }
    }

}