Spring Mybatis 基本使用过程(推荐)
作者:JOJO___
Mybatis是一个半自动ORM(Object Relational Mapping)框架,它可以简化数据库编程,让开发者更专注于SQL本身,本文给大家介绍Spring Mybatis 基本使用过程,感兴趣的朋友跟随小编一起看看吧
1. 简介
Mybatis库可以简化数据库的操作,专注于sql语句。
2.搭建步骤
2.1 在pom.xml引入mybatis
<dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.5.11</version> </dependency>
2.2 在resources下新建mybatis配置文件
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Mapper 3.0/EN" "https://mybatis.org/dtd/mybatis-3-config.dtd"> <configuration> <settings> <!-- <setting name="logImpl" value="STDOUT_LOGGING"/><!– 开启mybatis的日志输出 –>--> <setting name="mapUnderscoreToCamelCase" value="true"/><!-- 开启驼峰式自动映射 a_big => aBig --> </settings> <typeAliases> <typeAlias alias="goods" type="com.jojo.pojo.Goods"/><!-- 单独设置别名 --> <package name="com.jojo.pojo"/><!-- 批量设置别名, com.jojo.pojo包下的所有类名的别名为类的首字母小写--> </typeAliases> <environments default="development"> <environment id="development"> <transactionManager type="JDBC"/> <!-- 自动开启事务 --> <dataSource type="POOLED"><!-- mybatis维护连接池 --> <property name="driver" value="com.mysql.cj.jdbc.Driver"/> <property name="url" value="jdbc:mysql://localhost:3306/mybatis-example"/> <property name="username" value="root"/> <property name="password" value="a12345678"/> </dataSource> </environment> </environments> <mappers> <!-- 指定mapper xml文件的位置 --> <mapper resource="mappers/GoodsMapper.xml"/> </mappers> </configuration>
2.3 在resources/mapper下新建mapper的xml配置文件:
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0/EN" "https://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.jojo.mapper.GoodsMapper"><!-- 对应Mapper的全限定符 --> <!-- 这里写sql语句 --> <insert id="insert" useGeneratedKeys="true" keyColumn="id" keyProperty="id"> insert into goods (name) value(#{name}) </insert> <update id="update"> update goods set name=#{name} where id=#{id} </update> <delete id="delete"> delete from goods where id = #{id} </delete> <select id="selectById" resultType="goods"> select * from goods where id = #{id} </select> <select id="selectAll" resultType="goods"> select * from goods </select> </mapper>
2.4 新建pojo类
import lombok.Data; @Data//lombook插件的@Data标签可以自动生成get和set以及toString方法 public class Goods { private Integer id; private String name; }
2.5 新建mapper接口
public interface GoodsMapper { int insert(Goods goods); int update(Goods goods); int delete(Integer id); Goods selectById(Integer id); List<Goods> selectAll(); }
2.6 测试
public class MybatisTest { @Test public void test() throws IOException { //1.读取外部配置文件 InputStream ips = Resources.getResourceAsStream("mybatis-config.xml"); //2.创建sqlSessionFactory SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(ips); //3.根据sqlSessionFactory创建sqlSession SqlSession sqlSession = sqlSessionFactory.openSession(); //4.获取接口的代理对象,调用代理对象的方法就会查找mapper接口的方法 GoosdMapper mapper = sqlSession.getMapper(GoosdMapper.class); Goods goods = mapper.queryById(1); System.out.println(goods); //5.提交事务和释放资源 //sqlSession.commit(); sqlSession.close(); } }
3.常用mapper语句
3.1 传入值
<!-- #{id} = 使用占位符?,防止sql注入攻击,但不能替代表名表项--> <!-- ${id} = 不使用占位符?,不能防止sql注入攻击,但可以替代表名表项--> <select id="queryById" resultType="com.jojo.pojo.Employee"> select emp_id empId,emp_name empName, emp_salary empSalary from t_emp where emp_id = #{id} </select> <delete id="deleteById"> delete from t_emp where emp_id = #{id} <!-- 传入Integer类型,id可以改写成任意字符串--> </delete> <select id="queryBySalary" resultType="com.jojo.pojo.Employee"> select emp_id empId,emp_name empName, emp_salary empSalary from t_emp where empSalary = #{salary} <!-- 传入Double类型,salary可以改写成任意字符串--> </select> <insert id="insertEmp"> insert into t_emp (emp_name, emp_salary) values (#{empName},#{empSalary});<!-- 传入对象时,要写传入对象的属性 --> </insert> <select id="queryByNameAndSalary" resultType="com.jojo.pojo.Employee"> select emp_id empId,emp_name empName, emp_salary empSalary from t_emp where empSalary = #{a} and empName = #{b} <!-- 传入两个基本类型,根据接口中的@Param("名称")来指定--> </select> <select id="queryByNameAndSalary" resultType="com.jojo.pojo.Employee"> select emp_id empId,emp_name empName, emp_salary empSalary from t_emp where empSalary = #{arg0} and empName = #{arg1} <!-- 法2:传入两个基本类型,可以根据顺序来取arg0...arg1...--> </select> <select id="queryByNameAndSalary" resultType="com.jojo.pojo.Employee"> select emp_id empId,emp_name empName, emp_salary empSalary from t_emp where empSalary = #{param1} and empName = #{param2} <!-- 法3:传入两个基本类型,可以根据顺序来取param1...param2...--> </select> <insert id="insertEmpMap"> insert into t_emp (emp_name, emp_salary) values (#{name},#{salary});<!-- 传入Map时,要写传入Map的key --> </insert>
3.2 返回值
<select id="queryNameById" resultType="string"><!-- resultType指定返回的类型,写类的全限定符或者mybatis提供的别名(在mybatis官网查)--> select emp_name from t_emp where emp_id = #{id} </select> <select id="queryById" resultType="employee"> <!-- resultType指定返回的为对象时,select的行需要起别名来与类的属性完全一致--> select emp_id empId,emp_name empName, emp_salary empSalary from t_emp where emp_id = #{id} </select> <select id="queryById" resultType="employee"><!-- resultType指定返回的为对象时,开启驼峰映射(mapUnderscoreToCamelCase)后,select的行不再需要起别名来与类的属性完全一致--> select * from t_emp where emp_id = #{id} </select> <select id="selectEmpNameAndMaxSalary" resultType="map"> <!-- resultType返回的值没有未定义类时,可以用map接值,map的每一项的key对应一个列名 --> select emp_name 员工姓名, emp_salary 员工工资, (SELECT AVG(emp_salary) from t_emp) 部门平均工资 from t_emp where emp_salary=(select max(emp_salary) from t_emp) </select> <select id="queryNamesBySalary" resultType="string"><!--如果返回类型时List<String>,那么指定String即可--> select emp_name from t_emp where emp_salary > #{ salary}; </select> <select id="queryAll" resultType="employee"><!--如果返回类型时List<Employee>,那么指定Employee即可--> select * from t_emp; </select> <insert id="insertEmp" useGeneratedKeys="true" keyColumn="emp_id" keyProperty="empId"><!-- 主键自增长型:插入时,获取插入的id放在empId中 --> insert into t_emp (emp_name, emp_salary) value(#{empName},#{empSalary}); </insert> <insert id="insertTeacher"> <selectKey order="BEFORE" resultType="string" keyProperty="tId"> select replace(UUID(),'-',''); <!-- 插入前由数据库生成uuid并放在tId中--> </selectKey> insert into teacher (t_id,t_name) value (#{tId},#{tName}) </insert>
4.多表查询
4.1 一对一
1对1关系:一个A类中包含一个B类:
public class A { private Integer Id; private String aName; private Integer bId; private B b; } public class B { private Integer bId; private String bName; }
使用resultMap来装数据:
<resultMap id="aMap" type="a"> <!-- a的主键 id标签--> <id column="a_id" property="aId"/> <!-- order的普通列 custom标签--> <result column="a_name" property="aName"/> <result column="b_id" property="bId"/> <!-- 给第二层对象属性赋值 --> <association property="b" javaType="b"> <id column="b_id" property="bId"/> <result column="b_name" property="bName"></result> </association> </resultMap> <select id="queryAById" resultMap="aMap"> SELECT * FROM t_a ta join t_b tb on ta.b_id = tb.b_id where ta.a_id = #{id}; </select>
在config文件中加入:
<settings> <!-- 开启驼峰式自动映射 a_big => aBig --> <setting name="mapUnderscoreToCamelCase" value="true"/> <!-- 开启自动映射 a_big => aBig --> <setting name="autoMappingBehavior" value="FULL"/> </settings>
后可省略主键以外的映射关系:
<resultMap id="aMap" type="a"> <!-- a的主键 id标签--> <id column="a_id" property="aId"/> <!-- 给第二层对象属性赋值 --> <association property="b" javaType="b"> <id column="b_id" property="bId"/> </association> </resultMap> <select id="queryAById" resultMap="aMap"> SELECT * FROM t_a ta join t_b tb on ta.b_id = tb.b_id where ta.a_id = #{id}; </select>
4.2 一对多
1对多关系:一个A类中包含多个B类(List):
public class A { private Integer Id; private String aName; private Integer bId; private List<B> bList; } public class B { private Integer bId; private String bName; }
使用resultMap来装数据:
<resultMap id="aMap" type="a"> <id column="a_id" property="aId"/> <result column="a_name" property="aName"/> <result column="b_id" property="bId"/> <!--针对List<A>属性使用collection --> <collection property="bList" ofType="b"> <id column="b_id" property="bId"></id> <result column="b_name" property="bName"/> </collection> </resultMap> <select id="queryAList" resultMap="aMap"> select * from t_a ta join t_b tb on ta.customer_id = tb.customer_id </select>
在config文件中加入:
<settings> <!-- 开启驼峰式自动映射 a_big => aBig --> <setting name="mapUnderscoreToCamelCase" value="true"/> <!-- 开启自动映射 a_big => aBig --> <setting name="autoMappingBehavior" value="FULL"/> </settings>
后可省略主键以外的映射关系:
<resultMap id="aMap" type="a"> <id column="a_id" property="aId"/> <!--针对List<A>属性使用collection --> <collection property="bList" ofType="b"> <id column="b_id" property="bId"></id> </collection> </resultMap> <select id="queryAList" resultMap="aMap"> select * from t_a ta join t_b tb on ta.customer_id = tb.customer_id </select>
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