目录
简介
操作数据库
maven引入
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.4.5</version>
</dependency>
核心配置文件
SqlMapConfig.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>
<!--resource:加载外部配置文件，外部配置会替换内部配置-->
<properties resource="db.properties">
<!--配置内部属性-->
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="jdbc.username" value="root"/>
</properties>
<!--配置类型别名-->
<typeAliases>
<package name="com.XXX.pojo"/>
</typeAliases>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC" />
<dataSource type="POOLED">
<!--数据库配置-->
<property name="driver" value="${driver}" />
<property name="url" value="jdbc:mysql://127.0.0.1:3306/mybatisdb?characterEncoding=utf8" />
<property name="username" value="root" />
<property name="password" value="root" />
</dataSource>
</environment>
</environments>
<!--SqlMapConfig.xml:就是MyBatis的核心配置文件-->
<!--配置需要加载的Mapper.xml映射文件-->
<mappers>
<!--resource:需要加载的映射文件的文件地址-->
<!--<mapper resource="mapper/UserMapper.xml"/>-->
<!--使用类加载的方式加载资源-->
<!--前提1:名字一致,前提2:目录一致(在一起)-->
<!--<mapper class="com.XXX.mapper.UserDao"/>-->
<!--package使用包扫描的方式加载资源-->
<!--前提1:名字一致,前提2:目录一致(在一起)-->
<package name="com.XXX.mapper"/>
</mappers>
</configuration>
方式一（简单）
直接使用配置文件
配置
mapper/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="com.XXX.mapper.ProductMapper">
<select id="queryProductByPid" parameterType="int" resultType="com.XXX.pojo.Product">
SELECT * from product WHERE pid=#{pid};
</select>
</mapper>
操作
List<Product> list = sqlSession.selectList("queryProductByPid", 1);
方式二（old）
创建接口
PersonMapper.java
public interface ProductMapper {
List<Product> queryProductByPid(int pid);
}
配置mapper.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="com.XXX.mapper.ProductMapper">
<select id="queryProductByPid" parameterType="int" resultType="com.XXX.pojo.Product">
SELECT * from product WHERE pid=#{pid};
</select>
</mapper>
实现接口
ProductMapperImpl
public class ProductMapperImpl implements ProductMapper {
private SqlSessionFactory sqlSessionFactory;
public ProductMapperImpl(SqlSessionFactory sqlSessionFactory) {
this.sqlSessionFactory = sqlSessionFactory;
}
public List<Product> queryProductByPid(int pid) {
SqlSession sqlSession = sqlSessionFactory.openSession();
List<Product> list = sqlSession.selectList("queryProductByPid", pid);
return list;
}
}
操作
ProductMapper mapper = new ProductMapperImpl(sessionFactory);
List<Product> products = mapper.queryProductByPid(1);
方式三（常用）
创建接口
PersonMapper.java
public interface ProductMapper {
List<Product> queryProductByPid(int pid);
}
配置mapper.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="com.XXX.mapper.UserDao">
<!-- #{} 是传参数，防止sql注入 -->
<!-- ${} 是拼接，用于非参数的拼接 -->
<!--根据id查询-->
<select id="queryUserById" parameterType="int" resultType="UsEr">
select * FROM user WHERE id=#{id}
</select>
<!--根据用户名模糊查询,传入的时候加：%！！！-->
<select id="queryUserByUsername" parameterType="string" resultType="com.XXX.pojo.User">
select * from USER WHERE username like #{username}
</select>
<!--新增-->
<insert id="saveUser" parameterType="com.XXX.pojo.User">
<selectKey keyColumn="id" keyProperty="id" resultType="int" order="AFTER">
SELECT last_insert_id()
</selectKey>
insert into USER (username,birthday,sex,address) values (#{username},#{birthday},#{sex},#{address});
</insert>
</mapper>
操作
SqlSession sqlSession = sessionFactory.openSession();
ProductMapper mapper = sqlSession.getMapper(ProductMapper.class);
List<Product> products = mapper.queryProductByPid(1);
System.out.println(products);
配置详解
传入参数
<!--传入复杂参数-->
<select id="selectProduct2" parameterType="ProductVo" resultMap="product2">
SELECT * from product where pid>#{product.pid};
</select>
接收参数
<!--传出参数和数据库列名不一致-->
<resultMap id="product2" type="product2" autoMapping="true">
<id column="pid" property="pid"/>
<result column="category_id" property="cid"/>
</resultMap>
<select id="selectProduct2" parameterType="ProductVo" resultMap="product2">
SELECT * from product where pid>#{product.pid};
</select>
判断循环
<!--if判断-->
<select id="queryUserByUsernameAndSex" parameterType="user" resultType="user">
SELECT <include refid="fields"/> FROM `user`
<where>
<if test="sex!=null and sex!=''">
AND sex=#{sex}
</if>
<if test="username!=null and username!=''">
AND username LIKE #{username}
</if>
</where>
</select>
<!--代码片段-->
<sql id="fields">
id,username,birthday,sex,address
</sql>
<!--foreach-->
<select id="queryUserByIds" parameterType="queryVo" resultType="user">
SELECT <include refid="fields"/> FROM `user`
<where>
<foreach collection="ids" item="item" open="id in (" close=")" separator=",">
#{item}
</foreach>
</where>
</select>
一对一查询
<!--一对一查询,查询账号和对应的用户数据,方案一-->
<select id="queryAccountUserAll" resultType="accountUser">
SELECT a.*,u.username,u.address FROM account a LEFT JOIN `user` u ON a.UID=u.id
</select>
<!--配置一对一查询方案二的ResultMap-->
<resultMap id="accountResultMap" type="account" autoMapping="true">
<!--配置的Account的主键-->
<id property="id" column="id"/>
<result property="uid" column="uid"/>
<association property="user" javaType="user" autoMapping="true">
<id property="id" column="uid"/>
<result property="username" column="username"/>
</association>
</resultMap>
<!--一对一查询,查询账号和对应的用户数据,方案二(使用ResultMap)-->
<select id="queryAccountAll" resultMap="accountResultMap">
SELECT a.*,u.username,u.address FROM account a LEFT JOIN `user` u ON a.UID=u.id
</select>
一对多查询
<!--配置ResultMap-->
<resultMap id="userResultMap" type="user" autoMapping="true">
<id property="id" column="id"/>
<collection property="accounts" ofType="Account" autoMapping="true">
<id property="id" column="aid"/>
</collection>
</resultMap>
<!--查询所有的用户数据,使用一对多的方式,查询该用户的所有账号信息-->
<select id="queryUserAll" resultMap="userResultMap">
SELECT u.*,a.id aid,a.money FROM user u LEFT JOIN account a ON u.id=a.uid
</select>
延迟加载
- 先再总配置里面打开
<settings>
<!--开启延时加载-->
<setting name="lazyLoadingEnabled" value="true"/>
<setting name="aggressiveLazyLoading" value="false" />
</settings>
- 再在mapper.xml里面配置column和select
<!--一对一-->
<association property="user" javaType="user" column="uid"
select="com.alvin.mapper.UserMapper.queryUserById"></association>
<!--一对多-->
<collection property="accounts" ofType="Account" column="id"
select="com.alvin.mapper.AccountMapper.queryAccountByUid"></collection>
缓存
一级缓存
作用于具体sqlSession
默认开启
二级缓存
作用于指定mapper文件，如果在account.mapper里面操作user，有可能会影响user表的操作，所以一般不用。
- 核心配置文件（默认为true可以不设置）
<!--全局打开二级缓存-->
<setting name="cacheEnabled" value="true"/>
- 普通mapper.xml
<!--局部打开二级缓存-->
<cache/>
<!--useCache="true"打开某个select缓存-->
<select id="queryUserById" parameterType="int" resultType="user" useCache="true">
select * from user where id=#{id}
</select>
全注解开发
@Select("select * from user where id=#{id}")
public User queryUserById(Integer id);
@Select("select * from user")
public List<User> queryUserAll();
//@SelectKey:扩展,配置主键返回,statement:用来配置查询主键数据的sql
@SelectKey(statement = "select last_insert_id()", keyProperty = "id"
, keyColumn = "id", before = false, resultType = Integer.class)
@Insert("insert into user (username,birthday,sex,address) " +
"values (#{username},#{birthday},#{sex},#{address})")
public void saveUser(User user);
@Update("update user set username=#{username} where id=#{id}")
public void updateUserById(User user);
@Delete("delete from user where id=#{id}")
public void deleteUserById(Integer id);
//扩展:如果要使用动态sql的标签,需要给最终的sql语句用<script>标签进行包裹
@Select("<script>" +
"SELECT * FROM USER
" +
"<where>
" +
" <if test="sex!=null and sex!=''">
" +
" AND sex=#{sex}
" +
" </if>
" +
" <if test="username!=null and username!=''">
" +
" AND username like #{username}
" +
" </if>
" +
"</where>" +
"</script>")
public List<User> queryUserByUsernameAndSex(User user);
//查询所有的用户数据,使用延时加载的方式获取该用户的账户数据
//@Results:相当于在配置ResultMap
//@Result:相当于配置ResultMap里面的<id>和<result>标签
//@Result里面的id属性:就是这个配置是否是主键,如果是true,就代表这是主键,如果是false就不是主键
//@Result里面的property属性:就是配置对应的pojo的哪一个属性
//@Result里面的column属性:配置对应的数据库结果集的那一列,
// 如果是一对一和一对多,这里配置的就是延时加载的时候,需要使用的查询参数
//本例中延时加载账户的用户数据,就需要通过uid进行查询
//@Result注解里面没有ofType,而xml映射文件中有ofType,注解既然没有,就省略不写
//@Result里面的javaType就是属性的类型
//@Result里面的one配置的是一对一的延时加载,里面需要填写的是@One注解
//@One里面的select属性是配置延时加载需要执行的方法,和映射文件中延时加载的select属性配置的效果是一样
//@One里面的fetchType属性是配置是否使用延时加载,FetchType.LAZY代表使用延时加载
@Select("select * from user")
@Results({
@Result(id = true,property = "id",column = "id"),
@Result(property = "username",column = "username"),
@Result(property = "birthday",column = "birthday"),
@Result(property = "sex",column = "sex"),
@Result(property = "address",column = "address"),
@Result(property = "accounts",column = "id",
many = @Many(select = "com.alvin.mapper.AccountMapper.queryAccountByUid"))
})
public List<User> queryUserAccountAll();
//查询所有的账户数据,同时延时加载用户数据
@Select("select * from account")
@Results({
@Result(id = true, property = "id", column = "id"),
@Result(property = "uid", column = "uid"),
@Result(property = "money", column = "money"),
@Result(property = "user", column = "uid", javaType = User.class,
one = @One(select = "com.alvin.mapper.UserMapper.queryUserById")),
})
public List<Account> queryAccountUserAll();
//支持用户的延时加载账户信息,所编写的方法
@Select("select * from Account where uid=#{uid}")
public List<Account> queryAccountByUid(Integer uid);