java - Spring Data JPA Specification to Select Specific Columns

Question

We can select specific columns by writing custom @Query methods in our Repository Interface. However, I don't want to write so many methods for different properties.

I tried this, but it returns the entire object all the time.

public class MySpecifications {

    public static Specification<MyInfo> propertiesWithId(final String[] properties, final Object id, final String idProperty)
    {

        return new Specification<MyInfo>() {

            @Override
            public Predicate toPredicate(Root<MyInfo> root,
                    CriteriaQuery<?> query, CriteriaBuilder cb) {

                query = cb.createTupleQuery(); //tried cb.createQuery(MyInfo.class); as well

                List<Selection<? extends Object>> selectionList = new ArrayList<Selection<? extends Object>>();

                for (String property : properties) {

                    Selection<? extends Object> selection = root.get(property);

                    selectionList.add(selection);
                }

                return query.multiselect(selectionList).where(cb.equal(root.get(idProperty), id)).getRestriction();
            }

        };
    }
}

used as:

MyInfo findOne(Specification(properties,idValue, idProperty));

Is this the correct way? Where is the mistake?

Answer 1

The current spring data jpa specification executor is limited to criteria in the where clause, so you can't change the selected columns, it's implicitely limited to full entities only (take a look at JpaSpecificationExecutor interface documentation). You'll have to go with a custom repository implementation, or move to named queries-

Spring Data JPA and Querydsl to fetch subset of columns using bean/constructor projection