Spring Data JPA: Creating Specification Query Fetch Joins

Specification class:

public class MatchAllWithSymbol extends Specification<Gene> {
    private String symbol;

    public CustomSpec (String symbol) {
    this.symbol = symbol;
    }

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

        //This part allow to use this specification in pageable queries
        //but you must be aware that the results will be paged in   
        //application memory!
        Class clazz = query.getResultType();
        if (clazz.equals(Long.class) || clazz.equals(long.class))
            return null;

        //building the desired query
        root.fetch("aliases", JoinType.LEFT);
        root.fetch("attributes", JoinType.LEFT);
        query.distinct(true);        
        query.orderBy(cb.asc(root.get("entrezGeneId")));
        return cb.equal(root.get("symbol"), symbol);
    }
}

Usage:

    List<Gene> list = GeneRepository.findAll(new MatchAllWithSymbol("Symbol"));