JPA 条件查询与 Select 案例

Question

I'm writing JPA Criteria query with selectCase

CriteriaQuery<Tuple> query = builder.createTupleQuery();
Root<MyEntity> root = query.from(MyEntity.class);
Join document = ...
Join topic = ...


query.multiselect
(
        root.get("id"),
        document.get("id");
        builder.selectCase().when(builder.notEqual(document.get("id"), null), topic.get("id")),
        builder.selectCase().when(builder.notEqual(document.get("id"), null), topic.get("name")),
);
TypedQuery<Tuple> typedQuery = entityManager.createQuery(query);

The query works fine if I do not apply the 2 select cases.

But with above code I'm getting null pointer exception at entityManager.createQuery(query) .

My intention with select cases is to print topic's id & name when document's id is not null.

Exception :

java.lang.NullPointerException
    at org.hibernate.query.criteria.internal.predicate.ComparisonPredicate.render(ComparisonPredicate.java:172)
    at org.hibernate.query.criteria.internal.predicate.AbstractSimplePredicate.render(AbstractSimplePredicate.java:48)
    at org.hibernate.query.criteria.internal.Renderable.renderProjection(Renderable.java:34)

Please suggest what am I missing.

Edit: I've also tried:

builder.selectCase().when(builder.isNotNull(document), topic.get("id")),
    builder.selectCase().when(builder.isNotNull(document), topic.get("name"))

Answer 1

try add otherwhise:

builder.selectCase()
    .when(builder.isNotNull(document), topic.get("id"))
    .otherwhise(builder.literal("")), // assuming String is the type returned for the query
builder.selectCase()
    .when(builder.isNotNull(document), topic.get("name"))
    .otherwhise(builder.nullLiteral(String.class))    // assuming String is the type returned for the query