如何在JPA中查询哪个值为null的列？

Question

I am using JPA namedQuery to select data from DB.

 @NamedQuery(name = "Concept.findByRefTableNull", query = "SELECT c FROM Concept c WHERE c.conceptName = :conceptName and c.refTable = :refTable"),

///
 List<Concept> attributeList 
                = em.createNamedQuery("Concept.findByRefTableNull")
                .setParameter("conceptName", "student").
                setParameter("refTable", null).
                getResultList();

        System.out.println(attributeList.size()); //return 0

The List size is 0, but I am sure it should have records. The reason is the refTable. How to query a column which value is null in JPA ?

Thanks.

Answer 1

只需将您的查询更改为

 @NamedQuery(name = "Concept.findByRefTableNull", query = "SELECT c FROM Concept c WHERE c.conceptName = :conceptName and c.refTable IS NULL"),

Answer 2

I'm not sure if this is a Spring Data JPA feature only but I just write a method in the repository interface of the form findByFieldName(Type field) where fieldName is the name of the column I need to do a null check on. I then use this method and pass null as a parameter.

Answer 3

You can use Criteri Api , like this :

private Specification<Object> nullData(String field) {
    return (root, query, cb) ->
            cb.isNull(cb.lower(root.get(field)));
}

Answer 4

i would avoid Queries altogether - it pretty much negates the sense of persistence-abstraction. Create dynamic queries via the Criteria API instead, this will ensure portability AND you will be able to switch databases to some extent without much hassle