How to use Criteria Queries in Spring Boot Data Jpa Application

Question

I have an application that uses Spring Boot Data jpa . So far i am using a repository like this

public interface StudentRepository extends CrudRepos         


        

Answer 1

JPA 2 introduces a criteria API that can be used to build queries programmatically.

You can extend a new interface from JpaSpecificationExecutor

public interface CustomerRepository extends 
  CrudRepository, 
  JpaSpecificationExecutor {

  default List findCustomers() {
    return findAll(CustomerSpecs.findCustomers());
  }

Then create a customer specs

public final class CustomerSpecs {

    public static Specification findCustomers() {
        return new Specification() {
            public Predicate toPredicate(Root root, CriteriaQuery query,
            CriteriaBuilder builder) {

         LocalDate date = new LocalDate().minusYears(2);
         return builder.lessThan(root.get("birthday"), date);
      }
    };
}

The above can be simplified using lambdas as follows

public interface CustomerRepository extends 
  CrudRepository, 
  JpaSpecificationExecutor {

  default List findCustomers() {
    return findAll(
      (root, query, cb) -> {
         LocalDate date = new LocalDate().minusYears(2);
         return builder.lessThan(root.get("birthday"), date);
      }
    );
  }

For more details, refer this spring doc here

https://docs.spring.io/spring-data/jpa/docs/current/reference/html/#specifications