java queue 定义大小 java中query

一、Java中QueryWrapper的基本使用

 

1.单表查询

@GetMapping("/list")
public TableDataInfo list(Student student){
    LambdaQueryWrapper<Student> lqw = new LambdaQueryWrapper<Student>();
    lqw.eq(Student::getName, student.getName());
    lqw.like(Student::getClass,student.getClass());
    lqw.between("age",student.getAge1(),student.getAge2());
    lqw.orderByAsc("age");
    List<Student> list = studentService.list(lqw);
}

对应的sql语句为：

select * from student where name = '?' and class like '%?%' and age between '?' and '?' order by '?' asc

1.1、单表查询的基本用法

函数名	说明	例子
eq	等于	例：eq(“name”,“张子”) ===> name = ‘张子’
ne	不等于	例：ne(“name”,“张子”) ===> name <> ‘张子’
gt	大于	例：gt(“age”,“18”) ===> age>18
lt	小于	例：lt(“age”,“18”) ===> age<18
between	在值1到值2之间	例：between(“age”,18,30) ===> 18<age<30’
like	模糊查询	例：like(“name”,“张”) ===> name like ‘%张%’
isNull	字段为NULL	例：isNull(“name”) ===> name is null

 

2、多表查询

//Controller
@GetMapping("/listAndClass")
public TableDataInfo listAndClass(Student student)
{
    QueryWrapper<Student > qw = new QueryWrapper<Student >();
    if(StringUtils.isNotBlank(student.getName())){
        qw.eq("s.name",student.getName());
    }
    if(StringUtils.isNotBlank(student.getClassName())){
        qw.like("c.name",student.getClassName());
    }
    startPage();
    List<Student > list = studentService.listAndClass(qw);
    return getDataTable(list);
}

//Service
 List<Student> listAndClass(QueryWrapper<Student> qw);

//Service impl
@Override
public List<Student> listAndClass(QueryWrapper<Student> qw) {
    return this.getBaseMapper().listAndClass(qw);
}

//Mapper
@Select("select s.*,c.name from student s left join class c on s.id = c.student_id "+
        "${ew.customSqlSegment}")
List<YwSpaqjgDj> listAndClass(@Param(Constants.WRAPPER) QueryWrapper<Student> qw);