JDO Typesafe .vs. JPA Criteria

JPA2 introduced its "Criteria" queries, providing an API for typesafe query generation without the need to hardcode field names etc in queries; it built on the approach of Hibernate Criteria. DataNucleus includes a proposal for JDO "Typesafe" queries. It takes a slightly different approach aiming at usability and elegance. In this blog post we compare some queries using the two APIs.

In these examples we have two classes, Inventory and Product, where Inventory has a set of products.


Select of persistable objects with simple filter

JPQL single-string would be

SELECT p FROM Product p WHERE p.name = 'MP3 Extra'

whilst JDOQL single-string would be

SELECT FROM Product WHERE this.name == 'MP3 Extra'

JPA Criteria would be

CriteriaQuery<Product> criteria = builder.createQuery(Product.class);
Root<Product> productRoot = criteria.from(Product.class);
criteria.select(productRoot);
criteria.where(builder.equal(productRoot.get(Product_.name), "MP3 Extra"));
List<Product> products = em.createQuery(criteria).getResultList();

JDO Typesafe is

TypesafeQuery<Product> tq = pm.newTypesafeQuery(Product.class);
QProduct cand = QProduct.candidate();
List<Product> results = tq.filter(cand.name.eq("MP3 Extra")).executeList();

Select of result of attributes of persistable objects

JPQL single-string would be

SELECT p.value, p.manufacturer FROM Product p WHERE p.name = 'MP3 Extra'

JDOQL single-string would be

SELECT this.value, this.manufacturer FROM Product WHERE this.name == 'MP3 Extra'

JPA Criteria would be

CriteriaQuery criteria = builder.createQuery();
Root<Product> productRoot = criteria.from(Product.class);
criteria.multiselect(productRoot.get(Product_.value), 
productRoot.get(Product_.manufacturer);
criteria.where(builder.equal(productRoot.get(Product_.name), "MP3 Extra"));
List<Object[]> results = em.createQuery(criteria).getResultList();

JDO Typesafe is

TypesafeQuery<Product> tq = pm.newTypesafeQuery(Product.class);
QProduct cand = QProduct.candidate();
List<Object[]> results =
tq.filter(cand.name.eq("MP3 Extra"))
.executeResultList(cand.value, cand.manufacturer);

Select of aggregate of attribute of persistable objects

JPQL single-string would be

SELECT MAX(p.value) FROM Product p WHERE p.name = "MP3 Extra"

JDOQL single-string would be

SELECT MAX(this.value) FROM Product WHERE this.name == "MP3 Extra"

JPA Criteria would be

CriteriaQuery<Integer> criteria = builder.createQuery(Integer.class);
Root<Product> productRoot = criteria.from(Product.class);
criteria.select(builder.max(productRoot.get(Product_.value)));
criteria.where(builder.equal(productRoot.get(Product_.name), "MP3 Extra"));
Object result = em.createQuery(criteria).getSingleResult();

JDO Typesafe is

TypesafeQuery<Product> tq = pm.newTypesafeQuery(Product.class);
QProduct cand = QProduct.candidate();
Integer result =
tq.filter(cand.name.eq("MP3 Extra")).executeResultUnique(Integer.class, cand.value.max());

Select of persistable objects with simple filter and parameter

JPQL single-string would be

SELECT p FROM Product p WHERE p.name = :param

whilst JDOQL single-string would be

SELECT FROM Product WHERE this.name == :param

JPA Criteria would be

CriteriaQuery<Product> criteria = builder.createQuery(Product.class);
Root<Product> productRoot = criteria.from(Product.class);
criteria.select(productRoot);
ParameterExpression<String> valueParam = builder.parameter(String.class);
criteria.where(builder.equal(productRoot.get(Product_.name), valueParam));
TypedQuery<Product> query = em.createQuery(criteria);
query.setParameter(valueParam, "MP3 Extra");
List<Product> products = query.getResultList();

JDO Typesafe is

TypesafeQuery<Product> tq = pm.newTypesafeQuery(Product.class);
QProduct cand = QProduct.candidate();
List<Product> results =
tq.filter(cand.name.eq(tq.stringParameter("prefix")))
.setParameter("prefix", "MP3 Extra").executeList();

Select of persistable objects with joined filter condition

JPQL single-string would be

SELECT i FROM Inventory i JOIN i.products p WHERE (p.name = 'MP3 Extra')

JDOQL single-string would be

SELECT FROM Inventory WHERE this.products.contains(var) && var.name == "MP3 Extra"

JPA Criteria would be

CriteriaQuery<Inventory> criteria = builder.createQuery(Inventory.class);
Root<Inventory> invRoot = criteria.from(Inventory.class);
criteria.select(invRoot);
Join<Inventory, Product> productJoin = invRoot.join(Inventory_.products);
criteria.where(builder.equal(productJoin.get(Product_.name), "MP3 Extra"));
List<Inventory> inventories = em.createQuery(criteria).getResultList();

JDO Typesafe is

TypesafeQuery<Inventory> tq = pm.newTypesafeQuery(Inventory.class);
QProduct var = QProduct.variable("var");
QInventory cand = QInventory.candidate();
List<Inventory> results =
tq.filter(cand.products.contains(var).and(var.name.eq("MP3 Extra"))).executeList();

Select of persistable objects with subquery filter

JPQL single-string would be

SELECT p FROM Product p WHERE p.value < (SELECT AVG(q.value) FROM Product q)

JDOQL single-string would be

SELECT FROM Product WHERE this.value < (SELECT AVG(q.value) FROM Product q)

JPA Criteria would be

CriteriaQuery<Product> criteria = builder.createQuery(Product.class);
Root productRoot = criteria.from(Product.class);
criteria.select(productRoot);
Subquery<Double> sub = criteria.subquery(Double.class);
Root<Product> subRoot = sub.from(Product.class);
criteria.where(builder.lt(productRoot.get(Product_.value), 
sub.select(builder.avg(subRoot.get(Product_.value)))));
List<Product> products = em.createQuery(criteria).getResultList();

JDO Typesafe is

TypesafeQuery<Product> tq = pm.newTypesafeQuery(Product.class);
QProduct cand = QProduct.candidate();
TypesafeSubquery<Product> tqsub = tq.subquery(Product.class, "q");
QProduct candsub = QProduct.candidate("q");
List<Product> results = 
tq.filter(cand.value.lt(tqsub.selectUnique(candsub.value.avg()))).executeList();

As you have seen, for all typesafe queries JDO Typesafe is more elegant and shorter. It requires no "builder" too. Access of a field of a class is one particular example, typing "cand.value" instead of "productRoot.get(Product_.value)"