CriteriaOperator (CrOp)

CriteriaOperator is a lightweight, zero dependency, and type-safe wrapper around Java Persistence Criteria API, which simplifies building queries, particularly useful within REST SQL (RSQL) context.

Example of REST query that can be interpreted by the library:

http://localhost:64503/pets?birthdate.gte=2010-01-11&nickname.like=Ba

Which results in the following select:

select
    p1_0.id,
    p1_0.birthdate,
    p1_0.name,
    p1_0.pet_type_id 
from
    pet p1_0 
where
    p1_0.name like ? escape '' 
    and p1_0.birthdate>=?

There are a couple of easy steps to achieve the above:

1. Add the dependency

<dependency>
    <groupId>com.apulbere</groupId>
    <artifactId>crop</artifactId>
    <version>0.1.0</version>
</dependency>

2. Define a DTO that contains all fields necessary for filtering. For example, if you want to do filtering on String type then you choose StringCriteriaOperator from com.apulbere.crop.operator package.

@Getter
@Setter
public class PetSearchCriteria {
    private StringCriteriaOperator nickname;
    private LocalDateCriteriaOperator birthdate;
}

3. Create an instance of the service that will parse the query. It requires EntityManager in the constructor.

@Bean
CriteriaOperatorService cropService(EntityManager entityManager) {
    return new CriteriaOperatorService(entityManager);
}

4. Finally, invoke the service's create method with the root entity and filter object. The result is a builder that lets you match the entity's meta-model with each field from the DTO. When done, execute the query.

@GetMapping("/pets")
List<PetRecord> search(PetSearchCriteria petSearchCriteria) {
    return cropService.create(Pet.class, petSearchCriteria)
            .match(PetSearchCriteria::getNickname, Pet_.name)
            .match(PetSearchCriteria::getBirthdate, Pet_.birthdate)
            .getResultList()
            .stream()
            .map(petMapper::map)
            .toList();
}

For full example and to see all the capabilities of the library checkout pet-shop demo repository.