MyBatis延迟加载与立即加载案例教程

public class User implements Serializable {
 
    
 
 
    private Integer id;
    private String username;
    private Date birthday;
    private String sex;
    private String address;
    //一对多关系映射：主表实体应该包含从表实体的集合引用
    private List<Account> accounts;
 
    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", birthday=" + birthday +
                ", sex='" + sex + '\'' +
                ", address='" + address + '\'' +
                '}';
    }
 
    public List<Account> getAccounts() {
        return accounts;
    }
 
    public void setAccounts(List<Account> accounts) {
        this.accounts = accounts;
    }
 
    public Integer getId() {
        return id;
    }
 
    public void setId(Integer id) {
        this.id = id;
    }
 
    public String getUsername() {
        return username;
    }
 
    public void setUsername(String username) {
        this.username = username;
    }
 
    public Date getBirthday() {
        return birthday;
    }
 
    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }
 
    public String getSex() {
        return sex;
    }
 
    public void setSex(String sex) {
        this.sex = sex;
    }
 
    public String getAddress() {
        return address;
    }
 
    public void setAddress(String address) {
        this.address = address;
    }
 
}
 
public class Account implements Serializable {
    private Integer id;
    private Integer uid;
    private Double money;
 
    //一对一的关系中
    //从表实体应该包含一个主表实体的对象引用
    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 interface IUserDao {
    
    List<User> findAll();
 
    
    User findById(Integer i);
}
 
public interface IAccountDao {
    
    List<Account> findAll();
 
    
    Account findById(Integer i);
 
}

<?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">
<!--myBatis的主配置文件 -->
<configuration>
    <settings>
        <!--开启mybatis支持延迟加载-->
        <setting name="lazyLoadingEnabled" value="true"/>
        <setting name="aggressiveLazyLoading" value="false"/>
    </settings>
    <!--配置环境-->
    <environments default="Mysql">
        <!--配置mysql环境-->
        <environment id="mysql">
            <!--配置事务的类型-->
            <transactionManager type="JDBC"></transactionManager>
            <!--配置数据源（连接池）-->
            <dataSource type="POOLED">
                <!--配置连接数据库的基本信息-->
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/eesy"/>
                <property name="username" value="root"/>
                <property name="passWord" value="root"/>
            </dataSource>
        </environment>
    </environments>
    <!--映射文件 配置文件方式-->
    <mappers>
        <mapper resource="com/dynamic_annotation/dao/IAccountDao.xml"></mapper>
        <mapper resource="com/dynamic_annotation/dao/IUserDao.xml"></mapper>
    </mappers>
 
    
 
    <!--映射文件 注解方式(使用注解就要删除源配置文件)-->
   <!-- <mappers>
        <mapper class="com.dynamic_basics.dao.IUserDao"></mapper>
    </mappers>-->
</configuration>

<?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.dynamic_annotation.dao.IAccountDao">
 
    <!--定义封装account和user的resultMap-->
    <resultMap id="accountUserMap" type="com.dynamic_annotation.domain.Account">
        <id property="id" column="id"></id>
        <result property="uid" column="uid"></result>
        <result property="money" column="money"></result>
       
 
        <!--立即加载-->
        <!--使用select属性，使用其他DAO层的方法-->
     <association property="user" column="uid" javaType="com.dynamic_annotation.domain.User" select="com.dynamic_annotation.dao.IUserDao.findById">
 
     </association>
       </resultMap>
 
       <!--查询所有 id使用方法名-->
    <select id="findAll" resultMap="accountUserMap">
        select * from Account
    </select>
 
    <!--单个查询-->
    <select id="findById" parameterType="int" resultType="com.dynamic_annotation.domain.Account">
        select * from Account where uid=#{id}
    </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.dynamic_annotation.dao.IUserDao">
 
    <!--定义封装account和user的resultMap-->
    <resultMap id="userAccountMap" type="com.dynamic_annotation.domain.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>
      
       <!-- collection 是用于建立一对多中集合属性的对应关系
            ofType 用于指定集合元素的数据类型
            select 是用于指定查询账户的唯一标识（账户的 dao 全限定类名加上方法名称）
            column 是用于指定使用哪个字段的值作为条件查询
        -->
        <!--延迟加载-->
        <collection property="accounts" ofType="com.dynamic_annotation.domain.Account" select="com.dynamic_annotation.dao.IAccountDao.findById" column="id"></collection>
    </resultMap>
 
    <!--查询所有 id使用方法名-->
    <select id="findAll" resultMap="userAccountMap">
        select * from User
    </select>
 
    <!--根据id查询-->
    <select id="findById" parameterType="int" resultType="com.dynamic_annotation.domain.User">
        select * from user where id=#{id}
    </select>
 
 
</mapper>

public class AnnotationTest {
 
    private InputStream in;
    private SqlSession sqlSession;
    private IAccountDao accountDao;
    private IUserDao userDao;
 
    @Before
    public void init()throws Exception{
        //1.读取配置文件  Resources是myBatis封装的类
        in= Resources.getResourceAsStream("SqlMapConfig_anno.xml");
        //2.创建SQLSessionFactory工厂
        //  SqlSessionFactory factory=new SqlSessionFactoryBuilder().build(is);
        SqlSessionFactoryBuilder builder=new SqlSessionFactoryBuilder();
        SqlSessionFactory factory=builder.build(in);
        //3.使用工厂生产SQLSession对象
        sqlSession = factory.openSession();
        //4.使用SQLSession创建DAO接口的代理对象
        accountDao = sqlSession.getMapper(IAccountDao.class);
        userDao=sqlSession.getMapper(IUserDao.class);
    }
 
    @After
    public void destroy()throws Exception{
        //6.释放资源
        //提交事务
        sqlSession.commit();
        sqlSession.close();
        in.close();
    }
 
    //入门案例
    @Test
    public void testFindAllAccount(){
        List<Account> accounts = accountDao.findAll();
        System.out.println("------每个account的信息------");
        for (Account account : accounts) {
            System.out.println(account);
            System.out.println(account.getUser());
 
        }
    }
    @Test
    public void testFindAccount(){
           Account account = accountDao.findById(46);
        System.out.println(account);
    }
 
 
    @Test
    public void testFindAllUser(){
        List<User> users = userDao.findAll();
        for (User user : users) {
            System.out.println(user);
            System.out.println(user.getAccounts());
        }
    }
    @Test
    public void testFindUser(){
        User user = userDao.findById(49);
        System.out.println(user);
    }
}