Try to use this query instead of yours, this works perfectly with EclipseLink provider, not sure what your query is not working in eclipselink but works in hibernate, I tested the query below and you will be able to select Products based on a ProductCategoryName.
EntityManagerFactory emf = Persistence.createEntityManagerFactory("jpaQuery");
EntityManager em = emf.createEntityManager();
String category = "cat2";
CriteriaBuilder builder = em.getCriteriaBuilder();
CriteriaQuery<Products> query = builder.createQuery(Products.class);
Root<Products> products = query.from(Products.class);
Subquery<Productscategory> squery = query.subquery(Productscategory.class);
Root<Productscategory> productCategoryRoot = squery.from(Productscategory.class);
Join<Productscategory, Products> join = productCategoryRoot.join("productsCollection");
squery.select(productCategoryRoot)
.where(builder.equal(join, products), builder.equal(productCategoryRoot.get("productcatgoryname"), category));
query.where( builder.exists(squery));
List<Products> productList = em.createQuery(query).getResultList();
for (Products product : productList) {
System.out.println(product);
}
In which category is the name of the category you are trying to search..
This solved the problem =).. If this works, don't forget to accept the answer XD.