Mabitis
Mybatis
一、框架概念：
Java框架,一个软件半成品，简单来说就是一个别人搭好的舞台，你来做表演，说白了Java框架就是封装好方便程序员操作的类，使项目的开发更简单，维护起来也更容易。
而Mybatis框架是一个优秀的java持久层框架，他内部封装了jdbc，开发者只需要关注sql语句本身，其他繁琐的操作框架会替你完成。
二、入门：
1.开发dao：
1.1 原始dao开发模式
编写dao接口，编写dao实现类，存在大量重复代码！
1.2使用mapper代理开发模式（推荐）：
1.2.1配置xml：
*SqlMapConfig.xml的配置
<?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>
<properties resource="jdbc.properties"/>
<!--配置环境-->
<environments default="mysql">
<!--配置mysql的环境-->
<environment id="mysql">
<!--配置事务的类型-->
<transactionManager type="JDBC"/>
<!--配置数据源《连接池》-->
<dataSource type="POOLED">
<property name="driver" value="${DriverClassName}"/>
<property name="url" value="${url}"/>
<property name="username" value="${username}"/>
<property name="password" value="${password}"/>
</dataSource>
</environment>
</environments>
<!--指定映射配置文件的位置，映射配置文件指的是每个dao独立的配置文件-->
<mappers>
<mapper resource="Usermapper.xml"/>
</mappers>
</configuration>
*userMapper.xml配置：
<?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="cn.zzz.dao.Usermapper">
<!-- 配置方法，后面的为表面查询封装返回处-->
<select id="findAll" resultType="cn.zzz.domain.User">
select *from user
</select>
<!-- parameterType是对应的mapper接口方法接受的参数类型 -->
<insert id="saveUser" parameterType="cn.zzz.domain.User" useGeneratedKeys="true" keyProperty="id">
insert into user(username,birthday,sex,address) values (#{username},#{birthday},#{sex},#{addrsss});
</insert>
<update id="updateUser" parameterType="cn.zzz.domain.User">
update user set username=#{username},birthday=#{birthday},sex=#{sex},address=#{address} where id=#{id}
</update>
<delete id="deleteUser" parameterType="Integer">
delete from user where id = #{userid}
</delete>
</mapper>
*jdbc.properties配置：
DriverClassName=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/mybatis?useUnicode=true&characterEncoding=utf8
username=root
password=******
initialSize=5
maxActice=10
maxWait=3000
*测试方法：
public class MybatisTest {
private InputStream in;
private SqlSession session;
private Usermapper usermapper;
@Before
public void init() throws Exception{
in = Resources.getResourceAsStream("SqlMapConfig.xml");
//2.创建SqlsessionFactory工厂
SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
SqlSessionFactory factory = builder.build(in);
//3.使用工厂生产SqlSession对象
session = factory.openSession();
//4.使用SqlSession创建Dao接口的代理对象
usermapper = session.getMapper(Usermapper.class);
}
@After
public void destory()throws Exception{
session.close();;
in.close();
}
@Test
public void findAllTest() throws Exception {
//5.使用代理对象执行方法
List<User> users = usermapper.findAll();
for (User user : users) {
System.out.println(user);
}
}
@Test
public void saveUser(){
User user = new User();
user.setUsername("3241");
user.setBirthday(new Date());
user.setSex("男");
user.setAddrsss("1231241");
usermapper.saveUser(user);
session.commit();
System.out.println(user);
}
@Test
public void updateUser(){
User user = new User();
user.setId(53);
user.setUsername("155");
user.setBirthday(new Date());
user.setSex("男");
user.setAddrsss("544");
usermapper.updateUser(user);
session.commit();
}
@Test
public void deleteUser(){
User user = new User();
usermapper.deleteUser(49);
session.commit();
}
}
1.2.2注意事项：
*我的mysql安装为8.0，所以在url后面要加上 “?useUnicode=true&characterEncoding=utf8”
*主键回填：
一般id是主键，我们在插入信息时也不必主动去设置。数据库会自动增长，但插入成功后我们要得知插入数据的id是多少时，就得设置这2个：
useGeneratedKeys="true" keyProperty="id" 仅能在
例：
@Test
public void saveUser(){
User user = new User();
user.setUsername("3241");
user.setBirthday(new Date());
user.setSex("男");
user.setAddrsss("1231241");
usermapper.saveUser(user);
session.commit();
System.out.println(user);
}
没有加上时：打印出来的id为null，反之。
2.连接池
在SqlMapConfig.xml中配置：
1.POOLED：使用数据库连接池
2.UNPOOLED：不使用数据库连接池
3.JNDI
3.动态sql语句
where＋if语句:
<select id="findUserbyCondition" resultType="cn.zzz.domain.User">
select *from user
<where>
<if test="username!=null">
and username = #{username}
</if>
</where>
</select>
@Test
public void findUserbyCondition() throws Exception {
User user = new User();
user.setUsername("老王");
//5.使用代理对象执行方法
List<User> users = usermapper.findUserbyCondition(user);
for (User user1 : users) {
System.out.println(user1);
}
}
查询结果：
User{id=41, username='老王', birthday=Tue Feb 27 17:47:08 CST 2018, sex='男', addrsss='null'}
User{id=46, username='老王', birthday=Wed Mar 07 17:37:26 CST 2018, sex='男', addrsss='null'}
where+foreach:
<select id="findUserbyCondition" resultType="cn.zzz.domain.User">
select *from user
<where>
id in
<foreach collection="list" open="(" close=")" separator="," item="id" >
#{id}
</foreach>
</where>
</select>
public void findUserbyCondition() throws Exception {
List<Integer> list = new ArrayList<Integer>();
list.add(41);
list.add(42);
List<User> users = usermapper.findUserbyCondition(list);
for (User user : users) {
System.out.println(user);
}
}
查询结果：
User{id=41, username='老王', birthday=Tue Feb 27 17:47:08 CST 2018, sex='男', addrsss='null'}
User{id=42, username='小二王', birthday=Fri Mar 02 15:09:37 CST 2018, sex='女', addrsss='null'}
3.映射
一对一：
user类：
public class User {
private String username;
private String sex;
//以下省略get和set、toString方法
order类：
public class Order {
private int id;
private int userid;
private String number;
private User user;
//以下省略get和set、toString方法
OrderMapper.xml：
<mapper namespace="cn.zzz.dao.OrderMapper">
<resultMap id="orderMap" type="cn.zzz.domain.Order">
<id property="id" column="oid"></id>
<result property="userid" column="userid"></result>
<result property="number" column="number"></result>
<association property="user" javaType="cn.zzz.domain.User">
<result property="username" column="username"></result>
<result property="sex" column="sex"></result>
</association>
</resultMap>
<select id="findAll" resultMap="orderMap">
select u.*, o.id,o.userid,o.number from `order` o,`user` u where o.userid =u.id;
</select>
运行结果：
Order{id=1, userid=1, number='10000', user=User{username='是谁', id=1, sex='男'}}
Order{id=2, userid=5, number='11111', user=User{username='解开了', id=5, sex='男'}}
Order{id=3, userid=2, number='13431', user=User{username='老王', id=2, sex='男'}}
Order{id=4, userid=3, number='131231', user=User{username='哦哦', id=3, sex='女'}}
注意事项：
数据库的order表和user表的id最好不要相同，否则Mabatis会弄混，导致这样结果：
Order{id=1, userid=1, number='10000', user=User{username='是谁', id=1, sex='男'}}
Order{id=5, userid=5, number='11111', user=User{username='解开了', id=5, sex='男'}}
Order{id=2, userid=2, number='13431', user=User{username='老王', id=2, sex='男'}}
Order{id=3, userid=3, number='131231', user=User{username='哦哦', id=3, sex='女'}}
即order的id强制跟user的id相同
一对多：
Class类：
public class Class {
private Integer id;
private String name;
private List<Student> students;
}
Student类:
public class Student {
private Integer id;
private String name;
private String sex;
private Integer age;
}
ClassMapper.xml:
<mapper namespace="cn.zzz.dao.ClassMapper">
<resultMap id="classMap" type="cn.zzz.domain.Class">
<id property="id" column="c_id"/>
<result property="name" column="c_name"/>
<collection property="students" ofType="cn.zzz.domain.Student">
<id property="id" column="s_id"/>
<id property="name" column="s_name"/>
<id property="age" column="s_age"/>
<id property="sex" column="s_sex"/>
</collection>
</resultMap>
<select id="findAll" resultMap="classMap">
select s.*, c.* from tb_student s, tb_class c where s.s_c_id = c.c_id;
</select>
三.注解开发
CURD
使用注解开发便不需要mapper.xml这样的配置文件了
*下面是代码：
userMapper:
public interface UserMapper {
@Select("select *from user")
List<User> findAll();
@Insert("insert into user(username,sex) value(#{username},#{sex})")
void SaveUser(User user);
@Update("update user set username=#{username}, sex=#{sex} where id =#{id}")
void updateUser(User user);
@Delete("delete from user where id =#{id}")
void deleteUser(int id);
}
SqlMapConfig相关改动：
<mappers>
<mapper class="cn.zzz.dao.UserMapper"/>
</mappers>
一对一：
user表：
id username sex
1 是谁 男
2 老王 男
4 123 男
5 解开了 男
6 王二 女
user:
private int id;
private String username;
private Order order;
getter and setter 方法
toString 方法
order表：
id userid number
1 1 10000
2 5 11111
3 2 13431
4 3 131231
order:
private int oid;
private int userid;
private String number;
OrderMapper:
public interface OrderMapper {
@Select("select *from `order` where userid = #{id} ")
Order findOrderById(int id);
}
Usermapper:
public interface UserMapper {
@Select("select *from user")
@Results({
@Result(id = true,column = "id",property = "id"),
@Result(column = "username",property = "username"),
@Result(column = "sex",property = "sex"),
@Result(column = "id",property = "order",one = @One(select = "cn.zzz.dao.OrderMapper.findOrderById",fetchType = FetchType.EAGER))
})
List<User> findAll();
}
查询结果：
User{id=1, username='是谁', order=Order{oid=1, userid=1, number='10000', user=null}, sex='男'}
User{id=2, username='老王', order=Order{oid=3, userid=2, number='13431', user=null}, sex='男'}
User{id=4, username='123', order=null, sex='男'}
User{id=5, username='解开了', order=Order{oid=2, userid=5, number='11111', user=null}, sex='男'}
User{id=6, username='王二', order=null, sex='女'}
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