1. myBatis的介绍：
MyBatis是支持普通SQL查询，存储过程和高级映射的优秀持久层框架。MyBatis消除
了几乎所有的JDBC代码和参数的手工设置以及对结果集的检索。MyBatis可以使用简单的
XML或注解用于配置和原始映射，将接口和Java的POJO（Plain Old Java Objects，普通的
Java对象）映射成数据库中的记录。
jdbc-->dbutil-->(mybatis)-->hibernate
2. mybatis快速入门
a. 添加jar包
mybatis
asm-3.3.1.jar
cglib-2.2.2.jar
commons-logging-1.1.1.jar
log4j-1.2.16.jar
mybatis-3.1.1.jar
slf4j-api-1.6.2.jar
slf4j-log4j12-1.6.2.jar
mysql驱动
mysql-connector-java-5.1.7-bin.jar
b. 建库+表
create database mybatis;
use mybatis;
CREATE TABLE users(id INT PRIMARY KEY AUTO_INCREMENT, NAME VARCHAR(20), age INT);
INSERT INTO users(NAME, age) VALUES('Tom', 12);
INSERT INTO users(NAME, age) VALUES('Jack', 11);
c. 在应用的src下添加Mybatis的配置文件conf.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>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC" />
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver" />
<property name="url" value="jdbc:mysql://localhost:3306/mybatis" />
<property name="username" value="root" />
<property name="password" value="root" />
</dataSource>
</environment>
</environments>
</configuration>
d. 定义表所对应的实体类
public class User {
private int id;
private String name;
private int age;
}
e. 定义操作users表的sql映射文件userMapper.xml
<?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="org.mybatis.example.BlogMapper">
<select id="selectBlog" parameterType="int" resultType="Blog">
select * from Blog where id = #{id}
</select>
</mapper>
f. 在conf.xml文件中注册userMapper.xml文件
<mappers>
<mapper resource="com/atguigu/day03_mybatis/test1/userMapper.xml"/>
</mappers>
g. 编写测试代码：执行定义的select语句
public class Test {
public static void main(String[] args) throws IOException {
String resource = "conf.xml";
//加载mybatis的配置文件（它也加载关联的映射文件）
Reader reader = Resources.getResourceAsReader(resource);
//构建sqlSession的工厂
SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);
//创建能执行映射文件中sql的sqlSession
SqlSession session = sessionFactory.openSession();
//映射sql的标识字符串
String statement = "net.lamp.java.mybatis.bean.userMapper"+".selectUser";
//执行查询返回一个唯一user对象的sql
User user = session.selectOne(statement, 1);
System.out.println(user);
}
}
3. 编写基于mybatis的操作users表的CRUD操作的dao类
a. XML的实现：
1. 定义sql映射xml文件：
<insert id="insertUser" parameterType="net.lamp.java.ibatis.bean.User">
insert into users(name, age) values(#{name}, #{age});
</insert>
<delete id="deleteUser" parameterType="int">
delete from users where id=#{id}
</delete>
<update id="updateUser" parameterType="net.lamp.java.ibatis.bean.User">
update users set name=#{name},age=#{age} where id=#{id}
</update>
<select id="selectUser" parameterType="int" resultType="net.lamp.java.ibatis.bean.User">
select * from users where id=#{id}
</select>
<select id="selectAllUsers" resultType="net.lamp.java.ibatis.bean.User">
select * from users
</select>
2. 在config.xml中注册这个映射文件
<mapper resource="net/lamp/java/ibatis/bean/userMapper.xml"/>
3. 在dao中调用：
public User getUserById(int id) {
SqlSession session = sessionFactory.openSession();
User user = session.selectOne(URI+".selectUser", id);
return user;
}
b. 注解的实现：
1. 定义sql映射的接口
public interface UserMapper {
@Insert("insert into users(name, age) values(#{name}, #{age})")
public int insertUser(User user);
@Delete("delete from users where id=#{id}")
public int deleteUserById(int id);
@Update("update users set name=#{name},age=#{age} where id=#{id}")
public int updateUser(User user);
@Select("select * from users where id=#{id}")
public User getUserById(int id);
@Select("select * from users")
public List<User> getAllUser();
}
2. 在config中注册这个映射接口
<mapper class="net.lamp.java.ibatis.crud.ano.UserMapper"/>
3. 在dao类中调用
public User getUserById(int id) {
SqlSession session = sessionFactory.openSession();
UserMapper mapper = session.getMapper(UserMapper.class);
User user = mapper.getUserById(id);
return user;
}
4. 几个可以优化的地方
a. 连接数据库的几个配置可以单独放在一个properties文件中
db.properties
<properties resource="db.properties"/>
<property name="driver" value="${driver}" />
<property name="url" value="${url}" />
<property name="username" value="${username}" />
<property name="password" value="${password}" />
b. 为实体类定义别名,简化sql映射xml文件中的引用
<typeAliases>
<typeAlias type="net.lamp.java.ibatis.bean.User" alias="_User"/>
</typeAliases>
c. 可以在src下加入log4j的配置文件,打印日志信息(主要是sql语句)
1. log4j.properties
log4j.properties，
log4j.rootLogger=DEBUG, Console
#Console
log4j.appender.Console=org.apache.log4j.ConsoleAppender
log4j.appender.Console.layout=org.apache.log4j.PatternLayout
log4j.appender.Console.layout.ConversionPattern=%d [%t] %-5p [%c] - %m%n
log4j.logger.java.sql.ResultSet=INFO
log4j.logger.org.apache=INFO
log4j.logger.java.sql.Connection=DEBUG
log4j.logger.java.sql.Statement=DEBUG
log4j.logger.java.sql.PreparedStatement=DEBUG
2. log4j.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
<appender name="STDOUT" class="org.apache.log4j.ConsoleAppender">
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%-5p %d{MM-dd HH:mm:ss,SSS} %m (%F:%L)
" />
</layout>
</appender>
<logger name="java.sql">
<level value="debug" />
</logger>
<logger name="org.apache.ibatis">
<level value="debug" />
</logger>
<root>
<level value="debug" />
<appender-ref ref="STDOUT" />
</root>
</log4j:configuration>
5. 解决表的字段名与实体类的属性名不相同的冲突
a. 准备表和数据：
CREATE TABLE orders(
order_id INT PRIMARY KEY AUTO_INCREMENT,
order_no VARCHAR(20),
order_price FLOAT
);
INSERT INTO orders(order_no, order_price) VALUES('aaaa', 23);
INSERT INTO orders(order_no, order_price) VALUES('bbbb', 33);
INSERT INTO orders(order_no, order_price) VALUES('cccc', 22);
b. 定义实体类：
public class Order {
private int id;
private String orderNo;
private float price;
}
c. 实现getOrderById(id)的查询
c1. 通过在sql语句中定义别名
<select id="selectOrder" parameterType="int" resultType="_Order">
select order_id id, order_no orderNo,order_price price from orders where order_id=#{id}
</select>
c2. 定义<resultMap>
<select id="selectOrderResultMap" parameterType="int" resultMap="orderResultMap">
select * from orders where order_id=#{id}
</select>
<resultMap type="_Order" id="orderResultMap">
<id property="id" column="order_id"/>
<result property="orderNo" column="order_no"/>
<result property="price" column="order_price"/>
</resultMap>
6. 实现联表查询
1). 一对一：
a. 创建表和数据：
CREATE TABLE teacher(
t_id INT PRIMARY KEY AUTO_INCREMENT,
t_name VARCHAR(20)
);
CREATE TABLE class(
c_id INT PRIMARY KEY AUTO_INCREMENT,
c_name VARCHAR(20),
teacher_id INT
);
ALTER TABLE class ADD CONSTRAINT fk_teacher_id FOREIGN KEY (teacher_id) REFERENCES teacher(t_id);
INSERT INTO teacher(t_name) VALUES('LS1');
INSERT INTO teacher(t_name) VALUES('LS2');
INSERT INTO class(c_name, teacher_id) VALUES('bj_a', 1);
INSERT INTO class(c_name, teacher_id) VALUES('bj_b', 2);
b. 定义实体类：
public class Teacher {
private int id;
private String name;
}
public class Classes {
private int id;
private String name;
private Teacher teacher;
}
c. 定义sql映射文件ClassMapper.xml：
<!-- 方式一：嵌套查询方式, 通过执行另外一个SQL映射语句来返回预期的复杂类型 -->
<select id="getClasses" parameterType="int" resultMap="ClassesResultMap2">
select * from class where c_id=#{id}
</select>
<resultMap type="CLasses" id="ClassesResultMap2">
<id column="c_id" property="id"/>
<result column="c_name" property="name"/>
<association property="teacher" javaType="Teacher" column="teacher_id" select="getTeacher"></association>
</resultMap>
<select id="getTeacher" parameterType="int" resultType="Teacher">
select t_id id, t_name name from teacher where t_id=#{id}
</select>
<!--
方式二：嵌套结果：使用嵌套结果映射来处理重复的联合结果的子集
-->
<select id="getClasses2" parameterType="int" resultMap="ClassesResultMap">
select * from class c,teacher t where c.c_id=#{id} and c.teacher_id=t.t_id;
</select>
<resultMap type="Classes" id="ClassesResultMap">
<id column="c_id" property="id"/>
<result column="c_name" property="name"/>
<association column="teacher_id" property="teacher" javaType="Teacher">
<id column="t_id" property="id"/>
<result column="t_name" property="name"/>
</association>
</resultMap>
d. 测试：
@Test
public void testQueryOO() {
SqlSession session = factory.openSession();
Classes c = sqlSession.selectOne("com.atguigu.day03_mybatis.test5.CTMapper.getClasses", 1);
System.out.println(c);
}
@Test
public void testQueryOO2() {
SqlSession session = factory.openSession();
Classes c = sqlSession.selectOne("com.atguigu.day03_mybatis.test5.CTMapper.getClasses2", 1);
System.out.println(c);
}
2) 一对多
a. 创建表和数据：
CREATE TABLE student(
s_id INT PRIMARY KEY AUTO_INCREMENT,
s_name VARCHAR(20),
class_id INT
);
INSERT INTO student(s_name, class_id) VALUES('xs_B', 1);
INSERT INTO student(s_name, class_id) VALUES('xs_D', 1);
INSERT INTO student(s_name, class_id) VALUES('xs_E', 1);
INSERT INTO student(s_name, class_id) VALUES('xs_A', 2);
INSERT INTO student(s_name, class_id) VALUES('xs_H', 2);
INSERT INTO student(s_name, class_id) VALUES('xs_J', 2);
b. 定义实体类：
public class Student {
private int id;
private String name;
}
public class Classes {
private int id;
private String name;
private Teacher teacher;
private List<Student> students;
}
c. 定义sql映射文件ClassMapper.xml：(根据classId查询对应的班级信息,包括学生)
<!-- 集合的嵌套结果：使用嵌套结果映射来处理重复的联合结果的子集-->
<select id="getClasses3" parameterType="int" resultMap="ClassesResultMap3">
select * from class c,teacher t, student s where c.c_id=#{id} and c.teacher_id=t.t_id and s.class_id=c.c_id
</select>
<resultMap type="Classes" id="ClassesResultMap3">
<id column="c_id" property="id"/>
<result column="c_name" property="name"/>
<association column="teacher_id" property="teacher" javaType="Teacher">
<id column="t_id" property="id"/>
<result column="t_name" property="name"/>
</association>
<collection property="students" ofType="Student" javaType="ArrayList">
<id property="id" column="s_id" />
<result property="name" column="s_name"/>
</collection>
</resultMap>
<!-- 集合的嵌套查询方式, 通过执行另外一个SQL映射语句来返回预期的复杂类型 -->
<select id="getClasses4" parameterType="int" resultMap="ClassesResultMap4">
select * from class c where c.c_id=#{id}
</select>
<resultMap type="CLasses" id="ClassesResultMap4">
<id column="c_id" property="id"/>
<result column="c_name" property="name"/>
<association property="teacher" javaType="Teacher" column="teacher_id" select="getTeacher"></association>
<collection property="students" ofType="Teacher" column="c_id" select="getStudentsSelect" ></collection>
</resultMap>
<select id="getTeacher" parameterType="int" resultType="Teacher">
select t_id id, t_name name from teacher where t_id=#{id}
</select>
<select id="getStudentsSelect" parameterType="int" resultType="Student" >
select s_id id, s_name name from student where class_id=#{id}
</select>
d. 测试：
@Test
public void testQueryOT() {
SqlSession session = factory.openSession();
Classes classes = openSession.selectOne("com.atguigu.day03_mybatis.test6.OMMapper.getClasses3", 1);
System.out.println(c);
}
@Test
public void testQueryOT2() {
SqlSession session = factory.openSession();
Classes classes = openSession.selectOne("com.atguigu.day03_mybatis.test6.OMMapper.getClasses4", 1);
System.out.println(c);
}