如何在JPA中查询哪个值为null的列？ [英] How to query a column which value is null in JPA?

问题描述

我正在使用JPA namedQuery从DB中选择数据。

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

列表大小为0，但我确信它应该有记录。原因是refTable。如何在JPA中查询哪个值为空的列？

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 ?

谢谢。

推荐答案

只需将查询更改为

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

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