Understand the basics of Mybatis
Free learning recommendation: mysql video tutorial
##mybatis
mybatis-config.xml detailed configuration (when configuring, you must delete the redundant attributes and cannot have Chinese characters, otherwise an error will be reported!)<?xml version="1.0" encoding="UTF-8" ?>nbsp;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></setting> </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></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></package> </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></objectfactory> <!-- 插件:mybatis的插件,插件可以修改mybatis的内部运行规则 --> <plugins> <plugin></plugin> </plugins> <!-- 环境:配置mybatis的环境 --> <environments> <!-- 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> <!-- 事务管理器 --> <transactionmanager></transactionmanager> <!-- 数据源 配置连接我的数据库--> <datasource> <property></property> <property></property> <property></property> <property></property> </datasource> </environment> </environments> <!-- 数据库厂商标识 --> <databaseidprovider></databaseidprovider> <!-- 映射器:指定映射文件或者映射类 --> <mappers> <mapper></mapper> </mappers></configuration>
Paging
Reduce the amount of data access limt implements paging
sql statement: select * from table name limt 0,5;
- 0: The starting position of the data
- 5: Data length
The first type: using Mybatis 1 interface
List<user> getUserByLimit(Map<string> map);</string></user>
<select> select * from mybatis.user limit ${starIndex},${pageSize} </select>
<resultmap> <result></result> </resultmap>
@Test public void getUserByLimitTest() { SqlSession sqlSession = MyBatisUtils.getSqlSession (); UserMapper mapper = sqlSession.getMapper (UserMapper.class); HashMap hashMap = new HashMap<string> (); hashMap.put ("starIndex", 1); hashMap.put ("pageSize", 2); List userByLimit = mapper.getUserByLimit (hashMap); for (Object o : userByLimit) { System.out.println (o); } sqlSession.close (); }</string>
Second: Use RowBounds method 1. Interface
List getUserList();
2. Implement the interface
<select> 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 (); }</user>
Third method: Use Mybatis’ paging plug-in pageHeIper
sql Many-to-one processing
Database:
pojo The teacher-table table in the database corresponds to the entity class Teacher
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();</student>
<!-- 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> select * from mybatis.user; </select> <resultmap> <!-- 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></result> <result></result> <result></result> <!--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></association> </resultmap> <select> select * from mybatis.teacher_table where tid = #{id}; </select>
<!--2 多表联查--> <select> 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> <result></result> <result></result> <result></result> <result></result> <association> <result></result> </association> </resultmap>
<?xml version="1.0" encoding="UTF8" ?>nbsp;configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"><configuration> <properties></properties> <settings> <setting></setting> </settings> <typealiases> <typealias></typealias> <typealias></typealias> </typealiases> <environments> <environment> <transactionmanager></transactionmanager> <datasource> <property></property> <property></property> <property></property> <property></property> </datasource> </environment> </environments> <mappers> <!-- <mapper resource="com/kuang/w/dao/TeacherMapper.xml"></mapper> <mapper resource="com/kuang/w/dao/StudentMapper.xml"></mapper>--> <mapper></mapper> <mapper></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 (); }</student>
sql one-to-many processing
The entity class corresponding to the data table structure remains unchanged
First way: Multi-table joint query 1 interface
List<teacher> getTeacher(int tid);</teacher>
<select> 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> <result></result> <result></result> <!-- 复杂属性 对象用 :association 集合用:collection--> <collection> <!--javaType 指定属性类型 一个 Java 类的全限定名--> <result></result> <result></result> <result></result> <result></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 (); }</teacher>
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)Second way: Subquery1Interface
2 Implement interfaceList<teacher> getTeacher(int tid);</teacher>Copy after login3Test the same as above<!--第二种方式: 子查询--> <select> select * from mybatis.teacher_table where tid = #{tid}; </select> <resultmap> <!-- 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></result> <result></result> <collection> </collection> </resultmap> <select> select * from mybatis.user where tid = #{tid}; </select>Copy after login. . . .
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