Mybatis配置和基于配置的使用
导入jre包后还需要配置xml文件
配置文件mybatis-config.xml
在src目录下创建mybatis的主配置文件mybatis-config.xml
内容：
<?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>
//自动扫描com.blog.bean下的类型，使得在后续配置文件UserMapper.xml中使用resultType的时候，可以直接使用类名（User）,而不必写全com.blog.bena.User
<typeAliases>
<package name="com.blog.bean"/>
</typeAliases>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
//value:提供连接数据库用的驱动
<property name="driver" value="com.mysql.jdbc.Driver"/>
//value:数据库名称
<property name="url" value="jdbc:mysql://localhost:3306/blog"/>
//value:数据库账号
<property name="username" value="root"/>
//value:数据库密码
<property name="password" value="123456"/>
</dataSource>
</environment>
</environments>
//映射UserMapper.xml
<mappers>
<mapper resource="com/how2java/pojo/Category.xml"/>
</mappers>
</configuration>
在包com.blog.mapper下，新建文件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">
//表示命名空间是com.blog.mapper
<mapper namespace="com.blog.mapper">
//id: selectUserById 进行标示以供后续代码调用,resultType="User" 表示返回的数据和User关联起来，这里本应该使用的是 com.blog.bean.User, 但是因为上一步配置了别名，所以直接使用User就行了
<select id="selectUserById" resultType="User">
select * from user where uid = #{uid};
</select>
</mapper>
在java中调用：
//mybatis-config.xml文件路径：com.blog.config.mybatis-config.xml
String resource= "com/blog/config/mybatis-config.xml";
InputStream is = null;
try {
is = Resources.getResourceAsStream(resource);
} catch (IOException e) {
e.printStackTrace();
}
SqlSessionFactory ssf = new SqlSessionFactoryBuilder().build(is);
SqlSession sqlSession = ssf.getFactory().openSession();
//"com.blog.mapper.UserMapper.selectUserById"也可以写成"selectUserById",前提是多个配置文件下没有相同id
User u = (User)sqlSession .selectOne("selectUserById", 1);
添加:insert into
//parameterType参数类型为User类型
<insert id="addUser" parameterType="User">
insert into user(uname,usex,upass) values (#{uname},#{usex},#{upass});
</insert>
调用方式：
User u = new User("张三","男",123456);
sqlSession .insert("com.blog.mapper.UserMapper.addUser", user);
//在对数据库执行增加、修改、删除操作时，需要进行commit和close，否则无法生效并耗费资源
sqlSession.commit();
sqlSession.close();
删除：delete
<delete id="deleteUser">
delete from user where uid = #{uid};
s</delete>
查询：select
<select id="selectUserById" resultType="User">
select * from user where uid = #{uid};
</select>
修改：update
<update id="updateUser" parameterType="User" >
update User set uname=#{uname} where uid=#{uid}
</update>
查询对象的集合：
<select id="selectAllUser" resultType="User">
select * from user;
</select>
调用SqlSession对象的selectList("selectAllUser")方法
模糊查询：
<select id="listUserByUnameId" resultType="User">
select * from user where uname like concat('%',#{uname},'%')
</select>
多条件查询：例如分页,可以使用parameterType="map"，参数类型为map集合
<select id="listUserPage" parameterType="map" resultType="User">
select * from user limit #{begin},#{size}
</select>
调用方法：
Map<String ,Object> map = new HashMap<>();
map.put("begin", 0);
map.put("size", 3);
List<User> list = sqlSession.selectList("listUserPage", map);
一对多查询:collection、ofType
一个用户可以发多个博客，User类有个List<Blog> list属性
<resultMap type="User" id="Userpojo">
//子元素id代表resultMap的主键，而result代表其属性。
//id是作为唯一标识的，用在和其他对象实例对比时
<id column="uid" property="uid"/>
<result column="unick" property="unick"/>
//property: 指的是User类中Blog集合的变量名, ofType：指的是集合中元素的类型
<collection property="list" ofType="Blog">
<id column="bid" property="bid"/>
<result column="btitle" property="btitle"/>
</collection>
</resultMap>
<select id="selectUserAndBlogs" resultMap="Userpojo">
select unick,btitle from user inner join blog on buid=uid where uid=#{uid}
</select>
多对一查询：association、javaType
多个博客属于一个用户，Blog类有个User user属性
<resultMap type="Blog" id="Blogpojo">
<id column="bid" property="bid"/>
<result column="btitle" property="btitle"/>
//property: 指的是属性名称, javaType：指的是属性的类型
<association property="user" javaType="User">
<id column="uid" property="uid"/>
<result column="unick" property="unick"/>
</association>
</resultMap>
<select id="selectBlogAndUser" resultMap="Blogpojo">
select unick,btitle from blog inner join user on buid=uid
</select>
多对多查询：
一个用户可以发多个博客，User类有个List<Blog> listBlog属性，Blog有评论集合List<Comment> clist
<resultMap type="User" id="userblogscomments">
<id column="uid" property="uid"/>
<result column="unick" property="unick"/>
<collection property="list" ofType="Blog">
<id column="bid" property="bid"/>
<result column="btitle" property="btitle"/>
//在最内层的collection、association可以通过上层的结果集column，调用查询语句select直接查询
<collection property="clist" column="bid" select="selectCommentss">
</collection>
</collection>
</resultMap>
<select id="selectUserss" resultMap="userblogscomments" parameterType="int">
select * from user inner join blog on buid=uid where uid=#{uid}
</select>
<select id="selectCommentss" parameterType="int" resultType="Comment">
select * from comment where cbid=#{bid}
</select>
