了解Mybatis的基础

<?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核心配置  配置文件的根元素 --><configuration>     <!-- 属性：定义配置外在化 -->     <properties></properties>     <!-- 设置：定义mybatis的一些全局性设置 -->     <settings>         <!-- 具体的参数名和参数值 -->         <setting name="" value=""/>     </settings>     <!-- 类型名称：为一些类定义别名 -->     <typeAliases>         <!-- 实体类少 建议 第一种取别名方式-->         <typeAlias type="包路径" alias="别名"></typeAlias>         <!--实体类多 建议  第二种取别名方式         默认情况下用这种方式 别名为类名 首字母最好小写         -->         <package name="包名"/>     </typeAliases>     <!-- 类型处理器：定义Java类型与数据库中的数据类型之间的转换关系 -->     <typeHandlers></typeHandlers>     <!-- 对象工厂 -->     <objectFactory type=""></objectFactory>     <!-- 插件：mybatis的插件,插件可以修改mybatis的内部运行规则 -->     <plugins>         <plugin interceptor=""></plugin>     </plugins>     <!-- 环境：配置mybatis的环境 -->     <environments default="development">         <!-- 环境变量：可以配置多个环境变量，比如使用多数据源时，就需要配置多个环境变量 -->         <environment id="development">             <!-- 事务管理器 -->             <transactionManager type="JDBC"/>             <!-- 数据源 配置连接我的数据库-->             <dataSource type="POOLED">                 <property name="driver" value="com.mysql.jdbc.Driver"/>                 <property name="url"                           value="jdbc:mysql://localhost:3306/mybatis?serverTimezone=GMT%2B8&useSSL=true&useUnicode=true&characterEncoding=UTF-8"/>                 <property name="password" value="123"/>                 <property name="username" value="root"/>             </dataSource>         </environment>     </environments>     <!-- 数据库厂商标识 -->     <databaseIdProvider type=""></databaseIdProvider>     <!-- 映射器：指定映射文件或者映射类 -->     <mappers>         <mapper resource="com/kang/w/dao/impl/UserMapper.xml"></mapper>     </mappers></configuration>

  List<User> getUserByLimit(Map<String, Object> map);

   <select id="getUserByLimit" parameterType="map" resultType="user">         select *         from mybatis.user         limit ${starIndex},${pageSize}    </select>

<resultMap id="map" type="User">         <result property="pwd" column="password"></result>     </resultMap>

 @Test     public void getUserByLimitTest() {         SqlSession sqlSession = MyBatisUtils.getSqlSession ();         UserMapper mapper = sqlSession.getMapper (UserMapper.class);         HashMap hashMap = new HashMap<String, Object> ();         hashMap.put ("starIndex", 1);         hashMap.put ("pageSize", 2);         List userByLimit = mapper.getUserByLimit (hashMap);         for (Object o : userByLimit) {             System.out.println (o);         }          sqlSession.close ();     }

<select id="getUserList" resultType="user">         select *         from mybatis.user    </select>

 /**      * 测试使用RowBounds实现分页      */@Test     public void getUserByLimitRowBoundsTest() {         SqlSession sqlSession = MyBatisUtils.getSqlSession ();         RowBounds rowBounds = new RowBounds (0, 2);         List<User> userList = sqlSession.selectList ("com.kuang.w.dao.UserMapper.getUserList", null, rowBounds);         for (User user : userList) {             System.out.println (user);         }         //关闭         sqlSession.close ();     }

package com.kuang.w.pojo;  import lombok.Data;  /**  * @author W  */ @Data public class Teacher {     private int tId;     private String tName;  }

package com.kuang.w.pojo;import lombok.Data;/**  * @author W  */@Datapublic class Student {     private int id;     private int tid;     private String name;     private String password;     private Teacher teacher;}

   List<Student> getStudentList();

  <!-- 多对一查询     1 子查询 mysql 通过一个表里是数据   与另一个表的一个数据相的情况下 查询另一个的数据 一起显示   -->     <select id="getStudentList" resultMap="studentTeacher">         select *         from mybatis.user;    </select>     <resultMap id="studentTeacher" type="Student">         <!--  复杂属性 对象用 ：association 集合用：collection-->         <!--column 数据库中的字段 property 实体类中的属性-->         <result property="id" column="id"/>         <result property="name" column="name"/>         <result property="password" column="password"/>         <!--javaType	一个 Java 类的全限定名         ，或一个类型别名（关于内置的类型别名，可以参考上面的表格）。         如果你映射到一个 JavaBean，MyBatis 通常可以推断类型。         然而，如果你映射到的是 HashMap，         那么你应该明确地指定 javaType 来保证行为与期望的相一致。-->         <association property="teacher" column="tid" javaType="Teacher" select="getTeacher"></association>     </resultMap>     <select id="getTeacher" resultType="Teacher">         select *         from mybatis.teacher_table         where tid = #{id};    </select>

 <!--2 多表联查-->     <select id="getStudentList" resultMap="StudentList">         select u.id       uid,                u.name     uname,                u.password upassword,                u.tid      utid,                t.tname         from mybatis.user u,              mybatis.teacher_table t         where t.tid = u.tid;    </select>      <!-- 映射-->     <resultMap id="StudentList" type="Student">         <result column="uid" property="id"/>         <result column="utid" property="tid"/>         <result column="uname" property="name"/>         <result column="upassword" property="password"/>         <association property="teacher" javaType="Teacher">             <result property="tName" column="tname"></result>         </association>     </resultMap>

<?xml version="1.0" encoding="UTF8" ?><!DOCTYPE configuration         PUBLIC "-//mybatis.org//DTD Config 3.0//EN"         "http://mybatis.org/dtd/mybatis-3-config.dtd"><configuration>     <properties resource="db.properties"/>     <settings>         <setting name="logImpl" value="STDOUT_LOGGING"/>     </settings>     <typeAliases>         <typeAlias type="com.kuang.w.pojo.Teacher" alias="teacher"/>         <typeAlias type="com.kuang.w.pojo.Student" alias="student"/>     </typeAliases>      <environments default="development">         <environment id="development">             <transactionManager type="JDBC"/>             <dataSource type="POOLED">                 <property name="driver" value="${driver}"/>                 <property name="url" value="${url}"/>                 <property name="password" value="${password}"/>                 <property name="username" value="${username}"/>             </dataSource>         </environment>     </environments>     <mappers>         <!--   <mapper resource="com/kuang/w/dao/TeacherMapper.xml"></mapper>            <mapper resource="com/kuang/w/dao/StudentMapper.xml"></mapper>-->         <mapper class="com.kuang.w.dao.StudentMapper"></mapper>         <mapper class="com.kuang.w.dao.TeacherMapper"></mapper>     </mappers></configuration>

 @Test     public void getStudentListTest() {         SqlSession sqlSession = MyBatisUtils.getSqlSession ();         StudentMapper mapper = sqlSession.getMapper (StudentMapper.class);           List<Student> studentList = mapper.getStudentList ();         for (Student student : studentList) {             System.out.println (student);         }          sqlSession.commit ();         sqlSession.close ();     }

  <select id="getTeacher" resultMap="TeacherStudent">         select t.tid, t.tname, u.id, u.name, u.password         from mybatis.user u,              mybatis.teacher_table t         where t.tid = u.tid           and t.tid = #{tid};    </select>

<resultMap id="TeacherStudent" type="Teacher">         <result property="tName" column="tname"/>         <result property="tId" column="tid"/>         <!--  复杂属性 对象用 ：association 集合用：collection-->         <collection property="students" ofType="Student">             <!--javaType 指定属性类型 一个 Java 类的全限定名-->             <result column="id" property="id"></result>             <result column="name" property="name"></result>             <result column="password" property="password"></result>             <result column="tid" property="tid"></result>         </collection>     </resultMap>

 /*测试一对多*/     @Test     public void getTeacherTest2() {         SqlSession sqlSession = MyBatisUtils.getSqlSession ();         TeacherMapper mapper = sqlSession.getMapper (TeacherMapper.class);         List<Teacher> teacher = mapper.getTeacher (1);         for (Teacher teacher1 : teacher) {             System.out.println (teacher1);         }  		//提交事务   架子  这里可以不要         sqlSession.commit ();         // 关闭         sqlSession.close ();     }

com.intellij.rt.junit.JUnitStarter -ideVersion5 -junit4 com.kuang.w.dao.myTest,getTeacherTest2 Logging initialized using 'class org.apache.ibatis.logging.stdout.StdOutImpl' adapter.PooledDataSource forcefully closed/removed all connections.PooledDataSource forcefully closed/removed all connections.PooledDataSource forcefully closed/removed all connections.PooledDataSource forcefully closed/removed all connections.Opening JDBC Connection Created connection 164974746.Setting autocommit to false on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@9d5509a]==>  Preparing: select t.tid, t.tname, u.id, u.name, u.password from mybatis.user u, mybatis.teacher_table t where t.tid = u.tid and t.tid = ?; ==> Parameters: 1(Integer)<==    Columns: tid, tname, id, name, password<==        Row: 1, 狂神, 1, 天王盖地虎, 111<==        Row: 1, 狂神, 2, 小波, 123<==        Row: 1, 狂神, 3, 雷神, 922<==        Row: 1, 狂神, 5, 马儿扎哈, 123<==      Total: 4Teacher(tId=1, tName=狂神, students=[Student(id=1, tid=1, name=天王盖地虎, password=111), Student(id=2, tid=1, name=小波, password=123), Student(id=3, tid=1, name=雷神, password=922), Student(id=5, tid=1, name=马儿扎哈, password=123)])Resetting autocommit to true on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@9d5509a]Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@9d5509a]Returned connection 164974746 to pool.Process finished with exit code 0

 <!--第二种方式： 子查询-->     <select id="getTeacher3" resultMap="TeacherStudent3">         select *         from mybatis.teacher_table         where tid = #{tid};    </select>     <resultMap id="TeacherStudent3" type="Teacher">         <!--  复杂属性 对象用 ：association 集合用：collection         我们需要单独处理对象: association 集合: collection         javaType=""指定属性的类型!         集合中的泛型信息，我们使用ofType 获取         -->         <result column="tid" property="tId"/>         <result column="tname" property="tName"/>         <collection property="students" javaType="ArrayList" ofType="Student" select="getStudentByTeacherId"                     column="tid">         </collection>     </resultMap>     <select id="getStudentByTeacherId" resultType="Student">         select *         from mybatis.user         where tid = #{tid};    </select>