一、查询不显示全部列——select的使用

第一种情况——直接选定要显示的列

//    SELECT id,name FROM user WHERE (name LIKE ? AND age < ?)
    @Test
    public void selectByWrapperSupper(){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();

        queryWrapper.select("id","name").like("name","J").lt("age",20);

        List<User> userList = userMapper.selectList(queryWrapper);
        userList.forEach(System.out::println);
    }

第二种情况——反向设定不要显示的列（适用于要显示的列有很多的情况）

//    SELECT id,email FROM user WHERE (name LIKE ? AND age < ?) 
    @Test
    public void selectByWrapperSupper2(){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();

        queryWrapper.like("name","J").lt("age",20).select(User.class,
                info->!info.getColumn().equals("age")&&!info.getColumn().equals("name"));

        List<User> userList = userMapper.selectList(queryWrapper);
        userList.forEach(System.out::println);
    }

二、方法的第三个参数——condition执行条件的使用

//    SELECT id,name,age,email FROM user WHERE (name LIKE ?) 
    @Test
    public void testCondition(){
        String name = "J";
        String email = "";
        condition(name, email);
    }
    private void condition(String name,String email){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();

//        if(StringUtils.isNotBlank(name)){
//            queryWrapper.like("name", name);
//        }
//        if(StringUtils.isNotBlank(email)){
//            queryWrapper.like("email", email);
//        }

//        使用第三个参数condition参数来控制条件后
        queryWrapper.like(StringUtils.isNotBlank(name),"name",name)
                .like(StringUtils.isNotBlank(email), "email", email);

        List<User> userList = userMapper.selectList(queryWrapper);
        userList.forEach(System.out::println);
    }

三、当使用实体作为条件构造器的构造参数时

注1：实体作为构造参数和条件构造器单独设置的条件同时存在，所以注意不要设置重复了。

//    SELECT id,name,age,email FROM user WHERE name=? AND age=? AND (name LIKE ? AND age < ?)
    @Test
    public void selectByWrapperEntity(){
        User user = new User();
        user.setName("Jack");
        user.setAge(20);

        QueryWrapper<User> queryWrapper = new QueryWrapper<>(user);

        queryWrapper.like("name","J").lt("age",20);

        List<User> userList = userMapper.selectList(queryWrapper);
        userList.forEach(System.out::println);
    }

注2：实体作为构造参数传入后如果想做模糊查询，只需要在实体上对应字段添加注解

    @TableField(condition = SqlCondition.LIKE)
    private String name;

注3：%s表示字段，#{%s}表示字段对应的值，自定义一个条件

//    SELECT id,name,age,email FROM user WHERE name LIKE CONCAT('%',?,'%') AND age<? AND (name LIKE ? AND age < ?) 
    @TableField(condition = "%s&lt;#{%s}")
    private int age;

四、allEq用法

第一种情况：某个条件的值为null时，查出来的sql就是is null

//  SELECT id,name,age,email FROM user WHERE (name = ? AND age IS NULL) 
    @Test
    public void selectByWrapperAllEq(){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();

        Map<String,Object> params = new HashMap<>();
        params.put("name","Jack");
        params.put("age",null);
        queryWrapper.allEq(params);

        List<User> userList = userMapper.selectList(queryWrapper);
        userList.forEach(System.out::println);
    }

第二种情况：某个条件的值为null，allEq方法添加第二个参数为false时，查出来的sql忽略值为null的条件

//  SELECT id,name,age,email FROM user WHERE (name = ?) 
    @Test
    public void selectByWrapperAllEq(){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();

        Map<String,Object> params = new HashMap<>();
        params.put("name","Jack");
        params.put("age",null);
        queryWrapper.allEq(params,false);

        List<User> userList = userMapper.selectList(queryWrapper);
        userList.forEach(System.out::println);
    }

第三种情况：allEq方法中添加过滤条件参数，只保留符合条件的参数作为条件

//  SELECT id,name,age,email FROM user WHERE (age IS NULL)   
    @Test
    public void selectByWrapperAllEq2(){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();

        Map<String,Object> params = new HashMap<>();
        params.put("name","Jack");
        params.put("age",null);
        queryWrapper.allEq((k,v)->!k.equals("name"),params);

        List<User> userList = userMapper.selectList(queryWrapper);
        userList.forEach(System.out::println);
    }

第四种情况：在上面第三种情况基础上再添加第三个布尔条件为false，忽略值为null的条件

//  SELECT id,name,age,email FROM user 
    @Test
    public void selectByWrapperAllEq2(){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();

        Map<String,Object> params = new HashMap<>();
        params.put("name","Jack");
        params.put("age",null);
        queryWrapper.allEq((k,v)->!k.equals("name"),params,false);

        List<User> userList = userMapper.selectList(queryWrapper);
        userList.forEach(System.out::println);
    }

第五种情况：在上面基础上添加condition执行条件

//  SELECT id,name,age,email FROM user WHERE (name = ?)   
    @Test
    public void selectByWrapperAllEq2(){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();

        Map<String,Object> params = new HashMap<>();
        params.put("name","Jack");
        params.put("age",null);
        queryWrapper.allEq(StringUtils.isNotBlank((String)params.get("name")),(k,v)->!k.equals("age"),params,false);

        List<User> userList = userMapper.selectList(queryWrapper);
        userList.forEach(System.out::println);
    }