Mybatis的常用注解
@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
单表增删改查
1、环境准备
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.coydone</groupId>
<artifactId>mybatis01_annotation</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>jar</packaging>
<dependencies>
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.4.5</version>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.6</version>
</dependency>
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.12</version>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.10</version>
</dependency>
</dependencies>
</project>
resources下配置文件
数据库连接配置：jdbc.properties
jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/eesy_mybatis
jdbc.username=root
jdbc.password=root123
日志输出配置：log4j.properties
# Set root category priority to INFO and its only appender to CONSOLE.
#log4j.rootCategory=INFO, CONSOLE debug info warn error fatal
log4j.rootCategory=debug, CONSOLE, LOGFILE
# Set the enterprise logger category to FATAL and its only appender to CONSOLE.
log4j.logger.org.apache.axis.enterprise=FATAL, CONSOLE
# CONSOLE is set to be a ConsoleAppender using a PatternLayout.
log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=%d{ISO8601} %-6r [%15.15t] %-5p %30.30c %x - %m\n
# LOGFILE is set to be a File appender using a PatternLayout.
log4j.appender.LOGFILE=org.apache.log4j.FileAppender
log4j.appender.LOGFILE.File=d:\axis.log
log4j.appender.LOGFILE.Append=true
log4j.appender.LOGFILE.layout=org.apache.log4j.PatternLayout
log4j.appender.LOGFILE.layout.ConversionPattern=%d{ISO8601} %-6r [%15.15t] %-5p %30.30c %x - %m\n
Mybatis环境配置：mybatis-config.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>
<!-- 引入外部配置文件-->
<properties resource="jdbc.properties"></properties>
<!--配置别名-->
<typeAliases>
<package name="com.coydone.entity"></package>
</typeAliases>
<!-- 配置环境-->
<environments default="mysql">
<environment id="mysql">
<transactionManager type="JDBC"></transactionManager>
<dataSource type="POOLED">
<property name="driver" value="${jdbc.driver}"></property>
<property name="url" value="${jdbc.url}"></property>
<property name="username" value="${jdbc.username}"></property>
<property name="password" value="${jdbc.password}"></property>
</dataSource>
</environment>
</environments>
<!-- 指定带有注解的dao接口所在位置 -->
<mappers>
<package name="com.coydone.mapper"></package>
<!--<mapper class="com.coydone.mapper.UserMapper"></mapper>-->
</mappers>
</configuration>
2、编写实体类
实体类User
public class User implements Serializable {
private Integer id;
private String username;
private Date birthday;
private String sex;
private String address;
}
3、编写持久层接口Mapper。
持久层接口UserMapper.java
public interface UserMapper {
//查询所有用户
@Select("select * from user")
List<User> findAll();
@Insert("insert into user(username,address,sex,birthday)values(#{username},#{address},#{sex},#{birthday})")
void saveUser(User user);
@Update("update user set username=#{username},sex=#{sex},birthday=#{birthday},address=#{address} where id=#{id}")
void updateUser(User user);
@Delete("delete from user where id=#{id}")
void deleteUser(Integer id);
@Select("select * from user where id=#{id}")
User findById(Integer id);
// 根据用户名称模糊查询
@Select("select * from user where username like #{username}")
//@Select("select * from user where username like '%${value}%'")
List<User> findUserByName(String username);
@Select("select count(*) from user")
Integer findTotalUser();
}
4、编写测试类
public class AnnotationCRUDTest {
private InputStream in;
private SqlSessionFactory factory;
private SqlSession session;
private UserMapper userMapper;
@Before
public void init() throws Exception{
in = Resources.getResourceAsStream("mybatis-config.xml");
factory = new SqlSessionFactoryBuilder().build(in);
session = factory.openSession();
userDao = session.getMapper(UserMapper.class);
}
@After
public void destroy() throws Exception{
session.commit();
session.close();
in.close();
}
@Test
public void testSave(){
User user = new User();
user.setUsername("tom");
user.setAddress("北京市昌平区");
userMapper.saveUser(user);
}
@Test
public void testUpdate(){
User user = new User();
user.setId(51);
user.setUsername("tom");
user.setAddress("北京市昌平区");
user.setSex("男");
user.setBirthday(new Date());
userMapper.updateUser(user);
}
@Test
public void testDelete(){
userMapper.deleteUser(50);
}
@Test
public void testFindById(){
User user = userMapper.findById(51);
System.out.println(user);
}
@Test
public void testFindByName(){
List<User> users = userMapper.findUserByName("%王%");
//List<User> users = userMapper.findUserByName("王");
for (User user : users) {
System.out.println(user);
}
}
@Test
public void testFindTotal(){
Integer totalUser = userMapper.findTotalUser();
System.out.println(totalUser);
}
}
数据库字段名与实体类属性不对应时实体类
public class User implements Serializable {
private Integer userId;
private String userName;
private Date userBirthday;
private String userSex;
private String userAddress;
}
IUserDao
public interface IUserDao {
/**
* 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 = "address",property = "userAddress"),
@Result(column = "sex",property = "userSex"),
@Result(column = "birthday",property = "userBirthday")
})
List<User> findAll();
@Select("select * from user where id=#{id}")
@ResultMap("userMap")
User findById(Integer id);
}
多表查询
实现复杂关系映射之前我们可以在映射文件中通过配置来实现，在使用注解开发时我们需要借助@Results 注解，@Result 注解，@One 注解，@Many 注解。
复杂关系映射的注解说明
@Results 注解
代替的是标签<resultMap>
该注解中可以使用单个@Result 注解，也可以使用@Result 集合
@Results({@Result(),@Result()})或@Results(@Result())
@Result注解
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 注解（一对一）
代替了标签，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 注解（多对一）
代替了<Collection>标签，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。
注意：聚集元素用来处理“一对多”的关系。需要指定映射的 Java 实体类的属性，属性的 javaType（一般为 ArrayList）但是注解中可以不定义。
使用格式：@Result(property="",column="",many=@Many(select=""))
一对一及延迟加载
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。（注解方式实现）
创建Account的账户实体类
public class Account implements Serializable {
private Integer id;
private Integer uid;
private Double money;
//多对一（mybatis中称之为一对一）的映射，一个账户只能属于一个用户。
private User user;
}
持久层Mapper接口
public interface AccountMapper {
// 查询所有账户，并且获取每个账户所属的用户信息
@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="com.coydone.mapper.UserMapper.findById",fetchType= FetchType.EAGER))
})
List<Account> findAll();
}
测试类
public class AccountTest {
private InputStream in;
private SqlSessionFactory factory;
private SqlSession session;
private AccountMapper accountMapper;
@Before
public void init() throws Exception{
in = Resources.getResourceAsStream("mybatis-config.xml");
factory = new SqlSessionFactoryBuilder().build(in);
session = factory.openSession();
accountMapper = session.getMapper(AccountMapper.class);
}
@After
public void destroy() throws Exception{
session.commit();
session.close();
in.close();
}
@Test
public void testFindAll(){
List<Account> accounts = accountMapper.findAll();
for (Account account : accounts) {
System.out.println(account);
System.out.println(account.getUser());
}
}
}
一对多
查询所有用户并显示其对应的账户信息
public class User implements Serializable {
private Integer userId;
private String userName;
private Date userBirthday;
private String userSex;
private String userAddress;
//一对多关系映射：一个用户对于多个账户
private List<Account> accounts;
}
AccountMapper
//根据用户id查询账户信息
@Select("select * from account where uid=#{userId}")
List<Account> findAccountByUid(Integer userId);
UserMapper
public interface UserMapper {
//查询所有用户
@Select("select * from user")
@Results(id = "userMap",value = {
@Result(id = true,column = "id",property = "userId"),
@Result(column = "username",property = "userName"),
@Result(column = "address",property = "userAddress"),
@Result(column = "sex",property = "userSex"),
@Result(column = "birthday",property = "userBirthday"),
@Result(column = "id",property = "accounts",
many = @Many(select="com.coydone.mapper.AccountMapper.findAccountByUid",
fetchType = FetchType.LAZY))
})
List<User> findAll();
}
其中column = "id"是绑定User中的主键，property = "accounts"是User类中映射关系的属性名，select="com.coydone.mapper.AccountMapper.findAccountByUid"是通过用户id查询account表的全限定类名+方法名。
测试类
@Test
public void testFindAll(){
List<User> users = userMapper.findAll();
for (User user : users) {
System.out.println(user);
System.out.println(user.getAccounts());
}
}
开启二级缓存
@CacheNamespace(blocking = true)
public interface UserMapper {}
同时让Mybatis支持二级缓存，在mybatis-config.xml中开启。
<!--配置开启二级缓存-->
<settings>
<setting name="cacheEnabled" value="true"/>
</settings>
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