How can I use Spring's pagination (using Pageable) while writing a dynamic query using QueryDSL?

Question

I am trying to use pagination with QueryDSL - using the com.mysema.querydsl package.

All my Querydsl query types look like this -

@Generated("com.mysema.query.codegen.EntitySerializer")
public class QCountry extends EntityPathBase<Country> {...}

Currently, my repository implementation class looks something like this -

     @Override
            public Page<Country> findPaginatedCountries(String country, Optional<String> status, Pageable pageable) {

                QCountry qCountry= QCountry.someObject;
                QActiveCountry qActiveCountry = QActiveCountry.activeCountry;

               JPAQuery jpaQuery = new JPAQuery(entityManager);

                QueryBase queryBase = jpaQuery.from(qCountry).innerJoin(qActiveCountry).fetch()
                        .where(qCountry.codeLeft.country.upper().eq(country.toUpperCase()))
                        .where(qCountry.codeRight.country.upper().eq(country.toUpperCase()));



                if(status.isPresent()){
                    queryBase = queryBase.where(qActiveCountry.id(qCountry.active.id))
                            .where(qActiveCountry.status.upper().eq(status.get().toUpperCase()));
                }
.......}

Now, I want this dynamic query to return a paginated response. I want to use Spring's pagination to do that and not manually set offset, size etc.

I know I can use QueryDslRepositorySupport class - as implemented here - https://github.com/keke77/spring-data-jpa-sample/blob/master/spring-data-jpa/src/main/java/com/gmind7/bakery/employee/EmployeeRepositoryImpl.java

Sample code from the above link -

@Override
    public Page<Employees> QFindByOfficeCode(long officeCode, Pageable pageable) {
        //JPAQuery query = new JPAQuery(em);
        JPQLQuery query = from(QEmployees.employees).where(QEmployees.employees.officeCode.eq(officeCode));
        query = super.getQuerydsl().applyPagination(pageable, query);
        SearchResults<Employees> entitys = query.listResults(QEmployees.employees);
        return new PageImpl<Employees>(entitys.getResults(), pageable, entitys.getTotal());
    }      

However, to do that -

1. I need to pass JPQLQuery object to the applyPagination method. How can I do that without changing my code (Ofcourse, the repository class will extend QueryDslRepositorySupport class). Currently, I am using JPAQuery as you can see.

OR

2. I probably need to change my QueryDSL types by having them extend EntityPath instead of EntityPathBase so that I can use JPQLQuery.from() to generate the query and then use the applyPagination method, which requires a JPQLQuery object. However, my Q classes are extending EntityPathBase class instead. Should I be use com.querydsl package instead of com.mysemsa.querydsl package to generate query types?

OR

3. Other option is to use the following - http://docs.spring.io/spring-data/commons/docs/current/api/org/springframework/data/querydsl/QueryDslPredicateExecutor.html#findAll-com.querydsl.core.types.Predicate-org.springframework.data.domain.Pageable-

Code snippet below -

 Page<T> page = QueryDslPredicateExecutor.findAll(org.springframework.data.querydsl.Predicate predicate, Pageable pageable)

However, I am making joins between two tables and then filtering results with a where clause (as you can see above in my code). How can I pass a predicate object in the findAll method above? Not sure how to include a join in it.

Please let me know if the problem is not clear, I can add more details.

EDIT: There is a many to one relationship between Country and ActiveCountry. Country class has an ActiveCountry reference. And we have to do a join between both ids. Is is possible that Country can have null ActiveCountry. Therefore, we want an inner join - only non null values for active country

@ManyToOne
@JoinColumn(name="id")
ActiveCountry active;

Answer 1

Step 1: Annotate the entity class with @QueryEntity

@Entity
@QueryEntity
public class Country {}

This seems to have been addressed already since the question shows Q classes.

Step 2: Have the repository interface extend QueryDslPredicateExecutor

public interface CountryRepository
                 extends PagingAndSortingRepository<Country, Long>
                         , QueryDslPredicateExecutor<Country> {
}

Step 3: Invoke the Page<T> findAll(Predicate query, Pageable page) method provided by QueryDslPredicateExecutor

public Page<Country> getCountries(String country, Optional<String> status, Pageable page) {
  QCountry root = QCountry.country;

  BooleanExpression query = root.codeLeft.country.equalsIgnoreCase(country);
  query = query.and(root.codeRight.country.equalsIgnoreCase(country));

  if (status.isPresent()) {
    query = query.and(root.active.status.equalsIgnoreCase(status));
  }

  return countryRepository.findAll(query, page);
}