
MyBatis 注解开发
环境搭建
Mybatis 也可以使用注解开发方式,这样就可以减少编写 Mapper 映射文件。
常用注解说明:
-
@Insert
实现新增 -
@Update
实现更新 -
@Delete
实现删除 -
@Select
实现查询 -
@Result
实现结果集封装 -
@Results
可以与@Result
一起使用,封装多个结果集 -
@ResultMap
实现引用@Results
定义的封装 -
@One
实现一对一结果集封装 -
@Many
实现一对多结果集封装 -
@SelectProvider
实现动态 SQL 映射 -
@CacheNamespace
实现注解二级缓存的使用
单表 CRUD
实现复杂关系映射之前可以在映射文件中通过配置 <resultMap>
来实现,在使用注解开发时需要借助 @Results
注解,@Result
注解,@One
注解,@Many
注解。
-
@Results
代替了<id>
标签和<result>
标签,属性介绍:- id 是否是主键字段
- column 数据库的列名
- property 需要装配的属性名
- one 需要使用的 @One 注解
@Result(one=@One)()
- many 需要使用的 @Many 注解(
@Result(many=@Many)()
-
@One
(一对一) 代替了<assocation>
标签,是多表查询的关键,在注解中用来指定子查询返回单一对象,属性介绍:- select 指定用来多表查询的 sqlmapper
- fetchType 会覆盖全局的配置参数 lazyLoadingEnabled
- 使用格式:
@Result(column=" ", property="", one=@One(select=""))
-
@Many
(多对一)代替了<collection>
标签,是是多表查询的关键,在注解中用来指定子查询返回对象集合,- 使用格式:
@Result(property="", column="", many=@Many(select=""))
- 使用格式:
-
编写实体类
public class User implements Serializable {
private Integer id;
private String username;
private Date birthday;
private String sex;
private String address;
} -
使用注解方式开发持久层接口
package cn.parzulpan.dao; import cn.parzulpan.domain.User;
import org.apache.ibatis.annotations.*; import java.util.List; /**
* @Author : parzulpan
* @Time : 2020-12
* @Desc : 用户的持久层接口,使用注解开发
*/ public interface UserDAO { /**
* 查询所有用户
* @return
*/
@Select("select * from user")
@Results(id = "userMap",
value = {
@Result(id = true, column = "id", property = "userId"),
@Result(column = "username", property = "userName"),
@Result(column = "birthday", property = "userBirthday"),
@Result(column = "sex", property = "userSex"),
@Result(column = "address", property = "userAddress")
})
List<User> findAll(); /**
* 根据 id 查询一个用户
* @param userId
* @return
*/
@Select("select * from user where id = #{uid}")
@ResultMap(value = {"userMap"})
User findById(Integer userId); /**
* 插入操作
* @param user
* @return
*/
@Insert("insert into user(username, birthday, sex, address) values (#{userName}, #{userBirthday}, #{userSex}, #{userAddress})")
@SelectKey(keyColumn = "id", keyProperty = "userId", resultType = Integer.class, before = false,
statement = {"select last_insert_id()"})
int saveUser(User user); /**
* 更新操作
* @param user
* @return
*/
@Update("update user set username = #{userName}, birthday = #{userBirthday}, sex = #{userSex}, " +
"address = #{userAddress} where id = #{userId}")
int updateUser(User user); /**
* 删除操作
* @param userId
* @return
*/
@Delete("delete from user where id = #{uid}")
int deleteUser(Integer userId); /**
* 使用聚合函数查询
* @return
*/
@Select("select count(*) from user")
int findTotal(); /**
*
* @param name
* @return
*/
@Select("select * from user where username like #{username}")
@ResultMap(value = {"userMap"})
List<User> findByName(String name); } -
编写 SqlMapConfig 配置文件
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mabatis.org//DTD Congfig 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd"> <configuration>
<!-- 配置 properties 文件的位置 -->
<properties resource="JDBCConfig.properties"/> <!-- 配置别名 -->
<typeAliases>
<package name="cn.parzulpan.domain"/>
</typeAliases> <!-- 配置 MySQL 环境 -->
<environments default="mysql">
<environment id="mysql">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="${jdbc.driver}"/>
<property name="url" value="${jdbc.url}"/>
<property name="username" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
</dataSource>
</environment>
</environments> <!-- 配置映射信息 -->
<mappers>
<package name="cn.parzulpan.dao"/>
</mappers>
</configuration> -
编写测试方法
package cn.parzulpan; import cn.parzulpan.dao.UserDAO;
import cn.parzulpan.domain.User;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test; import java.io.InputStream;
import java.util.Date;
import java.util.List; /**
* @Author : parzulpan
* @Time : 2020-12
* @Desc :
*/ public class MyBatisAnnotationCRUDTest {
private InputStream is;
private SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
private SqlSessionFactory sqlSessionFactory;
private SqlSession sqlSession;
private UserDAO userDAO; @Before
public void init() throws Exception {
System.out.println("Before...");
is = Resources.getResourceAsStream("SqlMapConfig.xml");
sqlSessionFactory = builder.build(is);
sqlSession = sqlSessionFactory.openSession();
userDAO = sqlSession.getMapper(UserDAO.class);
} @After
public void destroy() throws Exception {
System.out.println("After...");
sqlSession.commit();
sqlSession.close();
is.close();
} @Test
public void findAllTest() {
List<User> users = userDAO.findAll();
for (User user : users) {
System.out.println(user);
}
} @Test
public void findByIdTest() {
User user = userDAO.findById(41);
System.out.println(user);
} @Test
public void saveUserTest() {
User user = new User(null, "annotation username", new Date(), "男", "Beijing");
System.out.println("save before: " + user); // User{id=null, ...}
int i = userDAO.saveUser(user);
System.out.println(i);
System.out.println("save after: " + user); // User{id=53, ...}
} @Test
public void updateUserTest() {
User user = userDAO.findById(42);
user.setUserName("Tom Tim Tom AA");
user.setUserAddress("瑞典");
int i = userDAO.updateUser(user);
System.out.println(i);
} @Test
public void deleteUserTest() {
int i = userDAO.deleteUser(53);
System.out.println(i);
} @Test
public void findTotalTest() {
int total = userDAO.findTotal();
System.out.println(total);
} @Test
public void findByNameTest() {
List<User> users = userDAO.findByName("%Tim%");
for (User user : users) {
System.out.println(user);
}
}
}
多表查询
一对一
需求:加载账户信息时并且加载该账户的用户信息,根据情况可实现延迟加载。
-
添加 User 实体类及 Account 实体类
public class Account implements Serializable {
private Integer id;
private Integer uid;
private Double money; private User user; // 一对一
} -
添加账户的持久层接口并使用注解配置
package cn.parzulpan.dao; import cn.parzulpan.domain.Account;
import org.apache.ibatis.annotations.One;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.mapping.FetchType; import java.util.List; /**
* @Author : parzulpan
* @Time : 2020-12
* @Desc :
*/ public interface AccountDAO { /**
* 查询所有账户,采用延迟加载的方式查询账户的所属用户
* @return
*/
@Select("select * from account")
@Results(id = "accountMap", value = {
@Result(id = true, column = "id", property = "id"),
@Result(column = "uid", property = "uid"),
@Result(column = "money", property = "money"),
@Result(column = "uid", property = "user", one = @One(select = "cn.parzulpan.dao.UserDAO.findById", fetchType = FetchType.LAZY))
})
List<Account> findAll();
} -
测试一对一关联及延迟加载
@Test
public void findAllTest() {
List<Account> accounts = accountDAO.findAll();
for (Account account : accounts) {
System.out.println();
System.out.println(account);
System.out.println(account.getUser());
}
}
``
一对多
需求:查询用户信息时,也要查询他的账户列表。使用注解方式实现。
-
User 实体类加入
List<Account>
public class User implements Serializable {
private Integer userId; // 注意这里的和数据库表的列名不一致
private String userName;
private Date userBirthday;
private String userSex;
private String userAddress; private List<Account> accounts; //一对多关系映射:主表方法应该包含一个从表方的集合引用
} -
编写用户的持久层接口并使用注解配置
public interface UserDAO {
/**
* 查询所有用户,包括账户列表
* @return
*/
@Select("select * from user")
@Results(id = "userMapWithAccount",
value = {
@Result(id = true, column = "id", property = "userId"),
@Result(column = "username", property = "userName"),
@Result(column = "birthday", property = "userBirthday"),
@Result(column = "sex", property = "userSex"),
@Result(column = "address", property = "userAddress"),
@Result(column = "id", property = "accounts", many = @Many(
select = "cn.parzulpan.dao.AccountDAO.findByUid",
fetchType = FetchType.LAZY
))
})
List<User> findAllWithAccount();
} -
编写账户的持久层接口并使用注解配置
public interface AccountDAO { /**
* 根据用户 id 查询用户下的所有账户
* @param userId
* @return
*/
@Select("select * from account where uid = #{uid} ")
List<Account> findByUid(Integer userId);
} -
添加测试方法
package cn.parzulpan; import cn.parzulpan.dao.UserDAO;
import cn.parzulpan.domain.Account;
import cn.parzulpan.domain.User;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test; import java.io.InputStream;
import java.util.List; /**
* @Author : parzulpan
* @Time : 2020-12
* @Desc :
*/ public class MyBatisAccountManyTest {
private InputStream is;
private SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
private SqlSessionFactory sqlSessionFactory;
private SqlSession sqlSession;
private UserDAO userDAO; @Before
public void init() throws Exception {
System.out.println("Before...");
is = Resources.getResourceAsStream("SqlMapConfig.xml");
sqlSessionFactory = builder.build(is);
sqlSession = sqlSessionFactory.openSession();
userDAO = sqlSession.getMapper(UserDAO.class);
} @After
public void destroy() throws Exception {
System.out.println("After...");
sqlSession.commit();
sqlSession.close();
is.close();
} @Test
public void findAllWithAccountTest() {
List<User> users = userDAO.findAllWithAccount();
for (User user : users) {
System.out.println();
System.out.println(user);
System.out.println(user.getAccounts());
}
}
}
缓存配置
-
在 SqlMapConfig 中开启二级缓存支持
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mabatis.org//DTD Congfig 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd"> <configuration>
<!-- 配置二级缓存 -->
<settings>
<!-- 开启二级缓存的支持 -->
<setting name="cacheEnabled" value="true"/>
</settings>
</configuration> -
在持久层接口中使用注解配置二级缓存
@CacheNamespace(blocking = true) // 基于注解方式实现配置二级缓存
public interface UserDAO {
} -
测试
@Test
public void findByIdHighCacheTest() {
SqlSession sqlSession1 = sqlSessionFactory.openSession();
UserDAO dao1 = sqlSession1.getMapper(UserDAO.class);
User user1 = dao1.findById(41);
System.out.println(user1.hashCode()); // 765284253
sqlSession1.close(); // 一级缓存消失 SqlSession sqlSession2 = sqlSessionFactory.openSession();
UserDAO dao2 = sqlSession2.getMapper(UserDAO.class);
User user2 = dao2.findById(41);
System.out.println(user2.hashCode()); // 1043351526
sqlSession1.close(); // 一级缓存消失 System.out.println(user1 == user2); // false }