MyBatis-Plus——使用查询构造器Wrapper & 简单分页操作

    @Test
    public void testAllEq() {
        QueryWrapper<Student> qw=new QueryWrapper<>();
        //将查询条件封装到Map集合中，and
        Map<String,Object> map=new HashMap<>();
        map.put("name","张三");
        map.put("age",22);
        qw.allEq(map);
        List<Student> students=mapper.selectList(qw);
        students.forEach( student -> System.out.println(student));
    }

    @Test
    public void testAllEq2() {
        QueryWrapper<Student> qw=new QueryWrapper<>();
        //将查询条件封装到Map集合中
        Map<String,Object> map=new HashMap<>();
        map.put("name","张三");
        map.put("age",null);
        /**
         * 第二个参数为 true：处理null值，where条件中加入 字段 IS NULL
         *         为 false：直接忽略null值，不添加到where子句中
         */
        qw.allEq(map,true);
        List<Student> students=mapper.selectList(qw);
        students.forEach( student -> System.out.println(student));
    }

    @Test
    public void testEq() {
        QueryWrapper<Student> qw=new QueryWrapper<>();
        //eq等于
        qw.eq("name","李四");
        List<Student> students=mapper.selectList(qw);
        students.forEach( student -> System.out.println(student));
    }

    @Test
    public void testNe() {
        QueryWrapper<Student> qw=new QueryWrapper<>();
        //ne不等于
        qw.ne("name","李四");
        List<Student> students=mapper.selectList(qw);
        students.forEach( student -> System.out.println(student));
    }

    @Test
    public void testGt() {
        QueryWrapper<Student> qw=new QueryWrapper<>();
        //gt大于，ge大于等于
        //lt小于，le小于等于
        qw.gt("age",25);
        List<Student> students=mapper.selectList(qw);
        students.forEach( student -> System.out.println(student));
    }

    @Test
    public void testBetween() {
        QueryWrapper<Student> qw=new QueryWrapper<>();
        //between在两个值的范围之间（闭区间）
        //notBetween不在两个值范围之间（对应上面集合的补集）
        qw.between("age",30,36);
        List<Student> students=mapper.selectList(qw);
        students.forEach( student -> System.out.println(student));
    }

    @Test
    public void testLike() {
        QueryWrapper<Student> qw=new QueryWrapper<>();
        //like 匹配值 "%值%"
        //notLike 不匹配 "%值%"
        qw.like("name","周");
        List<Student> students=mapper.selectList(qw);
        students.forEach( student -> System.out.println(student));
    }

    @Test
    public void testLikeLeft() {
        QueryWrapper<Student> qw=new QueryWrapper<>();
        //likeLeft 匹配 like "%值"
        //likeRight 匹配 like "值%"
        qw.likeLeft("name","三");
        List<Student> students=mapper.selectList(qw);
        students.forEach( student -> System.out.println(student));
    }

    @Test
    public void testIsNull() {
        QueryWrapper<Student> qw=new QueryWrapper<>();
        //isNull 判断字段值为 null
        //isNotNull 字段值不为 null
        qw.isNull("age");
        List<Student> students=mapper.selectList(qw);
        students.forEach( student -> System.out.println(student));
    }

    @Test
    public void testIn() {
        QueryWrapper<Student> qw=new QueryWrapper<>();
        //in 在这个值列表中，在列表中的都是符合条件的。
        //notIn 不在列表中的
//        List<String> list=new ArrayList<>();
//        list.add("张三");
//        list.add("李四");
//        qw.in("name",list);
        //下面这行等价于上面注释掉的四行
        qw.in("name","张三","李四");
        List<Student> students=mapper.selectList(qw);
        students.forEach( student -> System.out.println(student));
    }

    @Test
    public void testInSql() {
        QueryWrapper<Student> qw=new QueryWrapper<>();
        //inSql 常用来做子查询 类似 in()
        //notInSql 类似 notIn()
        qw.inSql("age","select age from student where id=2");
        List<Student> students=mapper.selectList(qw);
        students.forEach( student -> System.out.println(student));
    }

    @Test
    public void testGroupBy() {
        QueryWrapper<Student> qw=new QueryWrapper<>();
        qw.select("status,count(*)");
        //groupBy 基于多个字段分组
        qw.groupBy("status");
        List<Student> students=mapper.selectList(qw);
        students.forEach( student -> System.out.println(student));
    }

    @Test
    public void testOrderByAsc() {
        QueryWrapper<Student> qw=new QueryWrapper<>();
        //orderByAsc 按字段升序
        //orderByDesc 按字段降序
        //orderBy 每个字段指定排序方向
        qw.orderByAsc("age");
        List<Student> students=mapper.selectList(qw);
        students.forEach( student -> System.out.println(student));
    }

    @Test
    public void testOr() {
        QueryWrapper<Student> qw=new QueryWrapper<>();
        //or 连接条件用 or，默认是 and
        //and 连接条件用 and
        qw.eq("name","张三").or().eq("age",24);
        List<Student> students=mapper.selectList(qw);
        students.forEach( student -> System.out.println(student));
    }

    @Test
    public void testLast() {
        QueryWrapper<Student> qw=new QueryWrapper<>();
        //last 拼接 sql 语句
        qw.eq("name","张三").or().eq("age",24).last("limit 1");
        List<Student> students=mapper.selectList(qw);
        students.forEach( student -> System.out.println(student));
    }

    @Test
    public void testExists() {
        QueryWrapper<Student> qw=new QueryWrapper<>();
        //exists 拼接 exists ( sql 语句 )
        //notExists 是 exists 的相反操作
        qw.exists("select id,name from student where age>36");
        List<Student> students=mapper.selectList(qw);
        students.forEach( student -> System.out.println(student));
    }

package com.szh.mybatisplus.config;
import com.baomidou.mybatisplus.extension.plugins.PaginationInterceptor;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
/**
 *
 */
@Configuration
public class MyConfig {
    //分页插件
    @Bean
    public PaginationInterceptor paginationInterceptor() {
        return new PaginationInterceptor();
    }
}

    @Test
    public void testPage() {
        QueryWrapper<Student> qw=new QueryWrapper<>();
        qw.gt("age",20);
        qw.orderByAsc("id");
        //设置分页的数据
        IPage<Student> page=new Page<>();
        page.setCurrent(1);//第1页
        page.setSize(3);//每页3条记录
        IPage<Student> result = mapper.selectPage(page, qw);
        List<Student> students = result.getRecords();
        System.out.println("总页数：" + result.getPages());
        System.out.println("总记录数：" + result.getTotal());
        System.out.println("当前页码：" + result.getCurrent());
        System.out.println("每页大小：" + result.getSize());
        students.forEach( student -> System.out.println(student));
    }