使用 querydsl 按 null 搜索

Question

I have a controller method for searching like so

@RequestMapping(method = RequestMethod.GET)
public Page<MyEntity> find(@QuerydslPredicate(root = MyEntity.class)
                                     Predicate predicate,
                         Pageable pageable) {

    return this.myEntityRepository.findAll(predicate, pageable);
}

It works great. I can issue a GET request with various query string parameters, and it filters accordingly, but now I want to search by null. I tried doing something like /myentity?myParam1=& , but the predicate argument is always null .

How can I search where specific fields are null?

Answer 1

There is no way to search an entity by null parameters like myParam1=null , because it throws a NullPointerException. I had the same problem and this is the only way I could make it work.

@RequestMapping(method = RequestMethod.GET)
public Page find(@QuerydslPredicate(root = MyEntity.class) Predicate predicate, Pageable pageable, @RequestParam MultiValueMap parameters) {

    Page entities = myEntityRepository.findAll(predicate, pageable);
    if(parameters.get("myParam1") != null && 
            parameters.get("myParam1").get(0) != null &&
            parameters.get("myParam1").get(0).isEmpty()) {

        QEntity entity = QEntity.entity;
        BooleanExpression myParam1IsNull = entity.in(entities.getContent()).and(entities.myParam1.isNull());
        entities = myEntityRepository.findAll(myParam1IsNull, pageable);
    }

    return entities;
}

It performs two queries to the database, but it solves the problem. I hope this helps you.