简化jdbc操作，实现数据的持久化
MyBasti官网
http://www.mybatis.org/mybatis-3/zh/getting-started.html
简单使用MyBasti操作数据增删改
1.创建java项目转换meaven项目,导入pom.xml标签
<dependencies>
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.2.8</version>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.38</version>
</dependency>
<!-- log4j：日志文件 -->
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>
<!--延时加载: https://mvnrepository.com/artifact/cglib/cglib -->
<dependency>
<groupId>cglib</groupId>
<artifactId>cglib</artifactId>
<version>2.2.2</version>
</dependency>
</dependencies>
创建实体类Student-------------------
public class Student {
Integer id;
String name;
Integer age;
Date bd;
Classes classes;
set\get方法+构造函数
2.创建mybatis-3-config.xml
在src根目录下创建mybatis-3-config.xml 复制xml模板
<?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">
<!-- dtd是约束xml文件 -->
<configuration>
<!-- 链接数据库信息 通过default制定使用哪个数据库链接
也可以强行修改使用哪个
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream,"svn");
-->
<environments default="development">
<!-- 可创建多个数据库连接池 以id做唯一标识 -->
<environment id="development">
<!--事务提交方式:
JDBC:利用JDBC方式处理事务(commit rollback close)
MANAGED:将事务交由其他组件去托管(Spring,jobss)
-->
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql:///springjdbc"/>
<property name="username" value="root"/>
<property name="password" value="111"/>
</dataSource>
</environment>
<!-- 项目svn数据库 -->
<environment id="svn">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql:///springjdbc"/>
<property name="username" value="root"/>
<property name="password" value="111"/>
</dataSource>
</environment>
</environments>
<!-- 映射器 指明对数据库操作的配置文件
com.pb.mapper把.换成/
创建这个映射器文件
-->
<mappers>
<mapper resource="com/pb/mapper/StudentMapper.xml"/>
</mappers>
</configuration>
4.创建映射器文件xxxMapper.xml
src个根目录下创建package名为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">
<!-- namespace：传入接口文件 -->
<mapper namespace="com.pb.mapper.StudentMapper">
<!--操作sql
id:唯一标识
parameterType传入的参数类型 对象写路径,其他写类型 (这里写的是别名,在mybatis-config.xml配置)
resultType返回值类型
标签中间写sql语句 占位符#{属性名/对象属性值}
-->
<!--添加数据后展示添加的id 只适用于mysql sql有自增功能的数据库
useGeneratedKeys：获取自增的主键赋值给keyProperty,该属性只对insert语句有效
keyProperty:指明赋值的属性名字
-->
<insert id="insertStuden" parameterType="Student" useGeneratedKeys="true" keyProperty="id" >
insert into Student(stuname,age,brithday) values (#{name},#{age},#{bd})
</insert>
<!--
select * from Student where id=#{id}
输出:2-null-14-null
因为表字段名与实体类属性名不一致导致不能正确的映射
实体类 Mysql 赋值
Integer id; id 2
String name; stuname null
Integer age; age 14
Date bd; brithday null
使用别名处理>>>>>>>>>>>>>>>>>>>>>>>不推荐
select id id,stuname name,age age,brithday bd from Student where id=#{id}
-->
<select id="findById" parameterType="int" resultType="Student">
select id id,stuname name,age age,brithday bd from Student where id=#{id}
</select>
<!--
创建类与查询结果的映射:定义查询结果与类之间的映射关系,列名与属性名之间对应关系
type:对应类型
id:以xxxxResultMapper命名
主键方式:<id column="表里列名" property="实体类属性名"/>
其 他 列 :<result column="表里列名" property="实体类属性名"/>
-->
<resultMap type="Student" id="StudentResultMapper">
<id column="id" property="id"/>
<result column="stuname" property="name"/>
<result column="age" property="age"/>
<result column="brithday" property="bd"/>
</resultMap>
<!-- 使用结果映射 -->
<select id="findById2" parameterType="int" resultMap="StudentResultMapper">
select * from Student where id=#{id}
</select>
<update id="updateStudent" parameterType="Student">
update Student set stuname=#{name},age=#{age}, brithday=#{bd} where id=#{id}
</update>
<delete id="deleteStudent" parameterType="int">
delete from Student where id=#{id}
</delete>
<select id="selectAll" resultMap="StudentResultMapper">
select * from Student
</select>
<!--动态sql 在sql语句里添加循环遍历 -->
<select id="findByProperty" parameterType="Student" resultMap="StudentResultMapper">
select * from Student where 1=1
<if test="name!=null and name!=''">
and stuname like concat("%",#{name},"%")
</if>
</select>
</mapper>
根据StudentMapper创建接口文件
public interface StudentMapper {
void insertStuden(Student student);
Student findById(int id);
Student findById2(int id);
List<Student> selectAll();
void updateStudent(Student student);
void deleteStudent(int id);
List<Student> findByProperty(Student student);
}
5.测试类
public static void main(String[] args) {
SqlSession session= null;
try {
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
session=sqlSessionFactory.openSession();
//开启后需要关闭
Student student2=new Student(1,"n", 36, new Date());
/* 增删改打点出接口方法
session.getMapper(StudentMapper.class).deleteStudent(2);
*/
//模糊联合查
List<Student> students=session.getMapper(StudentMapper.class).findByProperty(student2);
for(Student student:students) {
System.out.println(student.getId()+"-"+student.getName()+"-"+student.getAge()+"-"+student.getBd());
}
//添加增删改的事务提交,不写的话即使sql语句正确但是信息不会被更改,并且自增列会自动自增
session.commit();
} catch (IOException e) {
e.printStackTrace();
}finally {
session.close();
}
}
延迟加载+联合查询
<?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">
<!-- namespace：传入接口文件 -->
<mapper namespace="com.pb.mapper.StudentMapper">
<!--添加数据后展示添加的id
useGeneratedKeys：获取自增的主键赋值给keyProperty,该属性只对insert语句有效
keyProperty:指明赋值的属性名字
<insert id="insertStuden" parameterType="Student" useGeneratedKeys="true" keyProperty="id" >
insert into Student(stuname,age,brithday) values (#{name},#{age},#{bd})
</insert>
-->
<!--
创建类与查询结果的映射:定义查询结果与类之间的映射关系,列名与属性名之间对应关系
type:对应类型
id:以xxxxResultMapper命名
主键方式:<id column="表里列名" property="实体类属性名"/>
其 他 列 :<result column="表里列名" property="实体类属性名"/>
<association property="对应类的属性名classes"
javaType="对应的java类别名Classes"
column="数据库对应的列class"
select="写一个查询的方法findClassById 用于2条语句联合查 "
resultMap="对应的结果集合 用于一条语句联合查">
</association>
使用findClassById查询classes对象结果赋值给association标签
-->
<resultMap type="Student" id="StudentResultMapper">
<id column="id" property="id"/>
<result column="stuname" property="name"/>
<result column="age" property="age"/>
<result column="brithday" property="bd"/>
<!--
<association property="classes" javaType="Classes" column="class_id" select="findClassById"></association>
-->
<association property="classes" javaType="Classes" column="class_id" resultMap="ClassesResultMapper"></association>
</resultMap>
<resultMap type="Classes" id="ClassesResultMapper">
<id column="class_id" property="id"/>
<result column="class_name" property="name" />
</resultMap>
<select id="findStudentById" parameterType="int" resultMap="StudentResultMapper">
select * from Student where id=#{id}
</select>
<select id="findClassById" parameterType="int" resultMap="ClassesResultMapper">
select * from class where class_id=#{id}
</select>
<!-- 联合查询 -->
<select id="findByJoin" parameterType="int" resultMap="StudentResultMapper">
SELECT s.*,c.* FROM student s JOIN `class` c ON s.`class_id` =c.`class_id` WHERE id=#{id}
</select>
</mapper>
在使用语句执行时结果为
Student stu=session.getMapper(StudentMapper.class).findStudentById(3);
System.out.println(stu.getName()+"-"+stu.getAge());
System.out.println(stu.getClasses());
12:00:24,492 DEBUG JdbcTransaction:98 - Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@66a3ffec]
12:00:24,494 DEBUG findStudentById:139 - ==> Preparing: select * from Student where id=?
12:00:24,510 DEBUG findStudentById:139 - ==> Parameters: 3(Integer)
12:00:24,524 DEBUG findClassById:139 - ====> Preparing: select * from class where class_id=?
12:00:24,524 DEBUG findClassById:139 - ====> Parameters: 1(Integer)
12:00:24,525 DEBUG findClassById:139 - <==== Total: 1
12:00:24,525 DEBUG findStudentById:139 - <== Total: 1
xiaoming-13
com.pb.entity.Classes@271053e1
从日志文件看出 语句是全部执行完后再输出结果,即使只输出一个结果2条查询语句也会照样执行,
而在使用延时加载后
12:03:59,173 DEBUG JdbcTransaction:98 - Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@6a4f787b]
12:03:59,174 DEBUG findStudentById:139 - ==> Preparing: select * from Student where id=?
12:03:59,191 DEBUG findStudentById:139 - ==> Parameters: 3(Integer)
12:03:59,250 DEBUG findStudentById:139 - <== Total: 1
xiaoming-13 ------------------执行的第一条
12:03:59,251 DEBUG findClassById:139 - ==> Preparing: select * from class where class_id=?
12:03:59,251 DEBUG findClassById:139 - ==> Parameters: 1(Integer)
12:03:59,251 DEBUG findClassById:139 - <== Total: 1
com.pb.entity.Classes@1a1d6a08-----执行的第二条
我们可以看出是执行一条查询语句后输出输出相应的语句 而在执行1条输出语句时会自动的执行相应的查询语句
---------------------------联合查询
联合查询我们分为2种模式
many2one 多对一 如多个学生对应1个班级 购物车商品列表对应1个user
one2many 一对多 如一个班级对应多个学生 1个user对应有多个购物车商品
联合查询对象
<association property="对应类的属性名classes"
javaType="对应的java类别名Classes"
column="数据库对应的列class"
select="写一个查询的方法findClassById 用于2条语句联合查 "
resultMap="对应的结果集合 用于一条语句联合查">
</association>
根据查询findStudentById语句中的class_id值查询findClassById返回结果 javaType="Classes"类型 >赋值给Student的classes属性 调用1个方法执行2句
<association property="classes" javaType="Classes" column="class_id" select="findClassById"> </association>
<select id="findStudentById" parameterType="int" resultMap="StudentResultMapper">
select * from Student where id=#{id}
</select>
<select id="findClassById" parameterType="int" resultMap="ClassesResultMapper">
select * from class where class_id=#{id}
</select>
调用findByJoin方法查询student+class 返回StudentResultMapper(也就是Student),其中property="classes"属性是联合查询中返回的resultMap="ClassesResultMapper"类的集合
<association property="classes" javaType="Classes" column="class_id" resultMap="ClassesResultMapper"></association>
<select id="findByJoin" parameterType="int" resultMap="StudentResultMapper">
SELECT s.*,c.* FROM student s JOIN `class` c ON s.`class_id` =c.`class_id` WHERE id=#{id}
</select>
one2many 模式 从班级角度去看学生:一个班级包含多个学生 我们从classes写代码
在classes类中添加Student集合
public class Classes {
Integer id;
String name;
List<Student> student=new ArrayList<>();
set\get方法....
修改config的映射器代码
<mappers>
<mapper resource="com/pb/mapper/ClassesMapper.xml"/>
</mappers>
Classesmapper.xml文件
public interface ClassesMapper {
Classes findByClassesId(int id);
}
<?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">
<!-- namespace：传入接口文件 -->
<mapper namespace="com.pb.mapper.ClassesMapper">
<resultMap type="Classes" id="ClassesResultMapper">
<id column="class_id" property="id"/>
<result column="class_name" property="name"/>
<!--
property="students"名字
javaType="ArrayList"类型
column="class_id"相对应外键的列
-->
使用collection标签运用集合
<collection property="student" javaType="ArrayList" column="class_id" select="findStudentsByClass"></collection>
</resultMap>
<resultMap type="Student" id="StudentResultMapper">
<id column="id" property="id"/>
<result column="stuname" property="name"/>
<result column="age" property="age"/>
<result column="brithday" property="bd"/>
</resultMap>
<select id="findByClassesId" parameterType="int" resultMap="ClassesResultMapper">
select * from class where class_id=#{id}
</select>
<select id="findStudentsByClass" parameterType="int" resultMap="StudentResultMapper">
select * from Student where class_id=#{id}
</select>
</mapper>
测试类测试代码
Classes cs=session.getMapper(ClassesMapper.class).findByClassesId(1);
System.out.println(cs.getId()+"\t"+cs.getName());
for(Student student:cs.getStudent()) {
System.out.println(student.getId()+"\t"+student.getName());
}
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