idea使用Mybatis逆向工程插件详情

 //作用：升序还是降序
 //参数格式：字段+空格+asc(desc)
 protected String orderByClause;  
 //作用：去除重复
 //true是选择不重复记录，false，反之
 protected boolean distinct;
 //自定义查询条件
 //Criteria的集合，集合中对象是由or连接
 protected List<Criteria> oredCriteria;
 // 分页的显示条数
 private Integer limit;
 // 分页的起始下标   
 private Long offset;
 //内部类Criteria包含一个Cretiron的集合，
 //每一个Criteria对象内包含的Cretiron之间是由  AND连接的
 public static class Criteria extends GeneratedCriteria {
  protected Criteria() {super();}
 }
 //是mybatis中逆向工程中的代码模型
 protected abstract static class GeneratedCriteria {......}
 //是最基本,最底层的Where条件，用于字段级的筛选
 public static class Criterion {......}

package org.ywz.test;
 
import org.junit.jupiter.api.Test;
import org.junit.platform.commons.util.StringUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.ywz.dao.StudentDao;
import org.ywz.pojo.Student;
import org.ywz.pojo.StudentExample;
 
import java.util.List;
 
/**
 * Example类使用说明
 */
@SpringBootTest
class MybatisDemoApplicationTests {
    @Autowired
    private StudentDao studentDao;
 
    @Test
    void contextLoads() {
        StudentExample studentExample = new StudentExample();
 
        // 查询数据的总条数 类似于：select count(*) from student
        long l = studentDao.countByExample(studentExample);
        System.out.println("---------------总条数----------------");
        System.out.println("数据库的总条数：" + l);
        System.out.println("----------------and条件---------------");
        // where条件查询或多条件查询
        Student student = new Student();
        student.setName("王五");
        student.setSex("男");
        selectAndCondition(student);
        System.out.println("---------------or条件----------------");
        selectOrCondition(student);
        System.out.println("-----------------模糊查询--------------");
        student.setName("王");
        selectLikeCondition(student);
        System.out.println("-----------------分页查询--------------");
        selectLimit();
    }
 
    /**
     * where条件查询或多条件查询
     * 类似于：select * from student where name={#student.name} and sex={#student.sex} order by score asc;
     *
     * @param student
     */
    private void selectAndCondition(Student student) {
        StudentExample studentExample = new StudentExample();
        StudentExample.Criteria criteria = studentExample.createCriteria();
        studentExample.setOrderByClause("score asc"); //升序
        studentExample.setDistinct(false); //不去重
        if (StringUtils.isNotBlank(student.getName())) {
            criteria.andNameEqualTo(student.getName());
        }
        if (StringUtils.isNotBlank(student.getSex())) {
            criteria.andSexEqualTo(student.getSex());
        }
        List<Student> students = studentDao.selectByExample(studentExample);
        students.forEach(System.out::println);
    }
 
    /**
     * 类似于：select * from student where name={#student.name} or sex={#student.sex} ;
     *
     * @param student
     */
    private void selectOrCondition(Student student) {
        StudentExample studentExample = new StudentExample();
        StudentExample.Criteria criteria1 = studentExample.createCriteria();
        StudentExample.Criteria criteria2 = studentExample.createCriteria();
        if (StringUtils.isNotBlank(student.getName())) {
            criteria1.andNameEqualTo(student.getName());
        }
        if (StringUtils.isNotBlank(student.getSex())) {
            criteria2.andSexEqualTo(student.getSex());
        }
        studentExample.or(criteria2);
        List<Student> students = studentDao.selectByExample(studentExample);
        students.forEach(System.out::println);
    }
 
    /**
     * 类似于：select * from student where name like %{#student.name}%
     *
     * @param student
     */
    private void selectLikeCondition(Student student) {
        StudentExample studentExample = new StudentExample();
        StudentExample.Criteria criteria = studentExample.createCriteria();
        if (StringUtils.isNotBlank(student.getName())) {
            criteria.andNameLike("%" + student.getName() + "%");
        }
        List<Student> students = studentDao.selectByExample(studentExample);
        students.forEach(System.out::println);
    }
 
    /**
     * 类似于：select * from student limit offset,limit
     */
    public void selectLimit() {
        StudentExample studentExample = new StudentExample();
        studentExample.setOffset(2l);
        studentExample.setLimit(5);
        List<Student> students = studentDao.selectByExample(studentExample);
        students.forEach(System.out::println);
    }
}