如何初始化Spring Data JPA的规范？

Question

I have a method that does a search with filters, so I'm using Specification to build a dynamic query:

public Page<Foo> searchFoo(@NotNull Foo probe, @NotNull Pageable pageable) {

        Specification<Foo> spec = Specification.where(null);  // is this ok?

        if(probe.getName() != null) {
            spec.and(FooSpecs.containsName(probe.getName()));
        }
        if(probe.getState() != null) {
            spec.and(FooSpecs.hasState(probe.getState()));
        }
        //and so on...

        return fooRepo.findAll(spec, pageable);
}

There is the possibility that there are no filters specified, so I would list everything without filtering. So having that in mind, how I should initialize spec ? Right now, the code above doesn't work as it always returns me the same result: all the registers of the table, no filtering have been aplied althought and operations have been made.

FooSpecs:

public class PrescriptionSpecs {

    public static Specification<Prescription> containsCode(String code) {
        return (root, criteriaQuery, criteriaBuilder) ->
            criteriaBuilder.like(root.get(Prescription_.code), "%" + code + "%");
    }

    // some methods matching objects...
    public static Specification<Prescription> hasContractor(Contractor contractor) {
        return (root, criteriaQuery, criteriaBuilder) ->
            criteriaBuilder.equal(root.get(Prescription_.contractor), contractor);
    }
    //... also some methods that access nested objects, not sure about this
    public static Specification<Prescription> containsUserCode(String userCode) {
        return (root, criteriaQuery, criteriaBuilder) ->
            criteriaBuilder.like(root.get(Prescription_.user).get(User_.code), "%" + userCode + "%");
    }
}

Answer 1

Specification.where(null) works just fine. It is annotated with @Nullable and the implementation handles null values as it should.

The problem is that you are using the and method as if it would modify the Specification , but it creates a new one. So you should use

spec = spec.and( ... );