mybatis配置文件详解(mybatis.cfg.xml)
environments
environment
-
DataSource
pooled-->连接池
-
TransactionManager
JDBC-->以JDBC的方式对数据库提交与回滚事务
properties
property
属性优先级问题
typeAliases
别名(不建议使用)
<typeAliases>
<typeAlias alias="User" type="org.apache.ibatis.submitted.complex_property.User"/>
</typeAliases>
typeHandlers
一般情况下我们不需要额外添加
settings
默认配置都是友好的
mappers
mapper的数量与javabean一致
<mappers>
<mapper resource="com.sz.mapper/GirlMapper.xml"/>
</mappers>
//下面是指定Mapper接口的包
<mappers>
<package name="com.mapper"/>
</mappers>
mybatis参数问题
<?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="com.sz.mapper.GirlMapper">//namespace属性必须是注册的Mapper。
<insert id="insert">
insert into girl(name,flower,birthday) values(#{name},#{flower},#{birthday})
</insert>
<select id="queryById" resultType="com.sz.pojo.Girl">
select * from girl where id=#{id}
</select>
</mapper>
mapper拥有4种子标签select insert update delete ,insert update delete只需要指定id属性,select只需要指定id,resultType属性,对于parameterType,这是入参类型,绝大部分情况下能够自我推断
传参问题
单个基本数据类型与String
如果仅仅是简单的一个单值传入,那么#{}表达式里面随便写什么都可以,只有一个参数,mybatis没有入参绑定的烦恼
多个基本数据类型或String入参问题
默认xml中的#{}里面放param1,param2或者arg0,arg1默认配置很不友好,不推荐使用
-
注解模式
GirlMapper中: Girl queryByNameFlower(@Param("name") String name,@Param("flower") String flower); GirlMapper.xml中: <select id="queryByNameFlower" resultType="com.sz.pojo.Girl"> select * from girl where name=#{name} and flower=#{flower} </select>
单个Javabean
默认通过javabean里面的属性的名称去引用,通过get方法去找这个值
MAP
GrilMapper中:
Girl queryByNameFlowerMap(Map<String,Object> map);
GrilMapper.xml中:
<select id="queryByNameFlowerMap" resultType="com.sz.pojo.Girl">
select * from girl where name=#{username} and flower=#{loveflower}
</select>
Test01中:
SqlSession sqlSession= MybatisUtil.getSession();
GirlMapper mapper=sqlSession.getMapper(GirlMapper.class);
Map<String,Object> map=new HashMap<>();
map.put("username","如花");
map.put("loveflower","hhhh");
Girl g=mapper.queryByNameFlowerMap(map);
System.out.println(g.getBirthday());
sqlSession.commit();
sqlSession.close();
动态SQL
OGNL
- if
- choose (when, otherwise)choose里面的when,自动匹配第一个满足的when
- trim (where, set)
- foreach
bind标签(解决模糊查询)
<select id="queryByName" resultType="com.sz.pojo.Girl">
<bind name="bin" value="'%'+name+'%'"></bind>
select * from girl
<where>
name like #{bin}
</where>
</select>
sql标签(减少重复代码)
<sql id="baseColumn">
name,flower,birthday
</sql>
<select id="queryAll" resultType="com.sz.pojo.Girl">
select
<include refid="baseColumn"></include>
from girl
</select>
Mybatis配置log4j
- 添加依赖
<!-- https://mvnrepository.com/artifact/log4j/log4j -->
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>
- 在resources里面新建一个log4j.properties
# Global logging configuration
log4j.rootLogger=ERROR, stdout
# MyBatis logging configuration...,com.sz.mapper是GirlMapper的包名
log4j.logger.com.sz.mapper=DEBUG
# Console output...
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p [%t] - %m%n
缓存
一级缓存(存储作用域为 Session):
MyBatis中一级缓存是默认开启的，即在查询中(一次SqlSession中)。只要当SqlSession不关闭，那么你的操作会默认存储使用一级缓存。
二级缓存(存储作用域为 Mapper(Namespace)):
mybatis.cfg.xml中:
<!--开启二级缓存-->
<settings>
<setting name="cacheEnabled" value="true"/>
</settings>
GirlMapper.xml中:
<mapper namespace="com.sz.mapper.GirlMapper">
<cache/>
</mapper>
如果开启了二级缓存,先去二级缓存中尝试命中,如果也无法命中,尝试去一级缓存中尝试命中,还不命中,再去数据库里面查询
二级缓存例子
SqlSession sqlSession= MybatisUtil.getSession();
SqlSession sqlSession2= MybatisUtil.getSession();
GirlMapper mapper=sqlSession.getMapper(
GirlMapper.class
);
GirlMapper mapper2=sqlSession2.getMapper(
GirlMapper.class
);
//使用二级缓存时，Girl类必须实现一个Serializable接口===> Girl implements Serializable
List<Girl> list = mapper.queryByName("花");
for (Girl g: list) {System.out.println(g.getName());}
sqlSession.commit();
/*一定要提交事务之后二级缓存才会起作用
因为，二级缓存是从cache（mapper.xml中定义的cache）中取得
如果session不commit，那么，数据就不会放入cache中*/
mapper2.queryByName("花");
//由于使用的是两个不同的SqlSession对象，所以即使查询条件相同，一级缓存也不会开启使用
sqlSession2.commit();
sqlSession.close();
sqlSession2.close();
放入二级缓存区的对象必须序列化
缓存失效方式:
- 如果查询之后进行增删改的行为,将导致缓存失效
- 强制清空缓存,SqlSession.clearCache();
对应关系
一对一
比如girl表对于girldetail表
<resultMap id="SelectMap" type="com.sz.pojo.GirlDetail">
<id column="id" jdbcType="BIGINT" property="id"></id>
<result column="gid" jdbcType="BIGINT" property="gid"></result>
<result column="phone" jdbcType="VARCHAR" property="phone" ></result>
<result column="address" jdbcType="VARCHAR" property="address" ></result>
<association property="girl" javaType="com.sz.pojo.Girl">
<id column="id" jdbcType="BIGINT" property="id"></id>
<result column="name" jdbcType="VARCHAR" property="name"></result>
<result column="flower" jdbcType="VARCHAR" property="flower" ></result>
<result column="birthday" jdbcType="DATE" property="birthday" ></result>
</association>
</resultMap>
<select id="queryByIdAndGid" resultMap="SelectMap">
select * from girldetail as b ,girl as a where a.id=#{id} and b.gid =#{id}
</select>
有个问题就是girl与girldetail表具有同名字段id,那么查询的id是哪个的呢?
在sql中,哪个表名在前面就是哪个表的id值,这里是girldetail在前面
解决方案
<resultMap id="SelectMap" type="com.sz.pojo.GirlDetail">
<id column="gd" jdbcType="BIGINT" property="id"></id>
<result column="gid" jdbcType="BIGINT" property="gid"></result>
<result column="phone" jdbcType="VARCHAR" property="phone" ></result>
<result column="address" jdbcType="VARCHAR" property="address" ></result>
<association property="girl" javaType="com.sz.pojo.Girl">
<id column="g" jdbcType="BIGINT" property="id"></id>
<result column="name" jdbcType="VARCHAR" property="name"></result>
<result column="flower" jdbcType="VARCHAR" property="flower" ></result>
<result column="birthday" jdbcType="DATE" property="birthday" ></result>
</association>
</resultMap>
<select id="queryByIdAndGid" resultMap="SelectMap">
SELECT b.id AS gd,a.id AS g FROM girldetail AS b ,girl AS a WHERE a.id=#{id} and b.gid =#{id}
</select>
注意resultMap可以继承
分步查询
一对多
<resultMap id="BaseMap" type="com.sz.pojo.Girl">
<id column="id" jdbcType="BIGINT" property="id"></id>
<result column="name" jdbcType="VARCHAR" property="name"></result>
<result column="flower" jdbcType="VARCHAR" property="flower" ></result>
<result column="birthday" jdbcType="DATE" property="birthday" ></result>
</resultMap>
<resultMap id="AllMap" extends="BaseMap" type="com.sz.pojo.All">
<collection property="blogList" ofType="com.sz.pojo.Blog">
<result column="title" jdbcType="VARCHAR" property="title"></result>
<result column="summary" jdbcType="VARCHAR" property="summary" ></result>
<result column="content" jdbcType="VARCHAR" property="content" ></result>
<collection property="commentList" ofType="com.sz.pojo.Comment">
<result column="contents" jdbcType="VARCHAR" property="contents" ></result>
</collection>
</collection>
</resultMap>
<select id="queryAllData" resultMap="AllMap">
SELECT * FROM girl AS t1,blog AS t2,COMMENT AS t3 WHERE t1.id=t2.u_id AND t2.id=t3.b_id;
</select>
javabean的设计:
public class All extends Girl{
private List<Blog> blogList;
}
public class Blog {
private int id;
private String title;
private String summary;
private String content;
private int u_id;
private List<Comment> commentList;
}
public class Comment {
private int id;
private String contents;
private int b_id;
}
数据库表设计与javabean设计
不管是一对一还是一对多的关系，外键约束都是在子表里面添加，想删除主表一条数据时，必须要把子表里对应的约束数据先删掉
如果是一对一:在子表的javabean中加一个父表的javabean的对象作为属性
如果是一对多:在父表的javabean中加一个集合，里面放子表对应的javabean的对象作为属性
