Querydsl vs. JPA Criteria

Querydsl and JPA Criteria are widely used frameworks for creating type-safe queries in Java. Both offer methods to express queries with static typing, simplifying the process of writing efficient and maintainable code for database interactions. Let’s delve into understanding the differences between JPA Criteria and Querydsl.

1. Introduction

In the world of Java development, interacting with databases efficiently and safely is crucial. Two popular frameworks that help in constructing type-safe queries are Querydsl and JPA Criteria. Both frameworks aim to provide a way to build queries in a way that leverages the Java-type system, reducing the likelihood of runtime errors and improving maintainability.

1.1 What is Querydsl?

Querydsl is a framework that allows the construction of type-safe queries for various backends including JPA, SQL, MongoDB, and more. It provides a fluent API for building queries, which makes the code more readable and maintainable. Querydsl generates query types from your domain model, enabling you to write queries in a statically typed manner.

1.1.1 Key Features of Querydsl

• Type Safety: Queries are constructed using the generated Q-types, ensuring compile-time type checking.
• Fluent API: The fluent API makes the query construction process intuitive and easy to read.
• Multi-Backend Support: Querydsl supports various backends like JPA, SQL, MongoDB, and more.
• Integration: It integrates seamlessly with Spring Data JPA, allowing for powerful query capabilities in Spring-based applications.

1.2 What is JPA Criteria?

JPA Criteria API is part of the Java Persistence API (JPA) specification. It provides a way to build queries using a strongly typed, object-oriented approach. This API is built into JPA and provides a programmatic way to create queries, avoiding the need to write JPQL (Java Persistence Query Language) or SQL directly.

1.2.1 Key Features of JPA Criteria

• Type Safety: Similar to Querydsl, the JPA Criteria API ensures that queries are type-safe at compile time.
• Standardization: As part of the JPA specification, it is a standard API that works across all JPA implementations.
• Dynamic Query Construction: It allows dynamic construction of queries based on the criteria provided at runtime.
• Integration: It is built into the JPA specification and integrates well with all JPA providers.

1.3 Comparison of Querydsl and JPA Criteria

Both Querydsl and JPA Criteria provide type-safe query construction capabilities, but they differ in their approach and features:

• Ease of Use: Querydsl is generally considered easier to use due to its fluent API and auto-generated Q-types, which make the query syntax more readable and intuitive. JPA Criteria, on the other hand, can be more verbose and complex, especially for more complicated queries
• Flexibility: Querydsl offers more flexibility by supporting multiple backends, whereas JPA Criteria is limited to JPA implementations. This makes Querydsl a more versatile choice for projects that may interact with different types of databases or need to switch between them
• Integration: Both frameworks integrate well with Spring Data JPA, but Querydsl has a slight edge due to its built-in support through the QuerydslPredicateExecutor interface. This allows for seamless integration and powerful query capabilities in Spring applications

2. Important Methods in Querydsl and JPA Criteria

2.1 Key Methods in Querydsl

QUser user = QUser.user;
List<User> users = queryFactory.selectFrom(user).fetch();

List<User> users = queryFactory.selectFrom(user)
.where(user.age.gt(18))
.fetch();

QOrder order = QOrder.order;
List<User> users = queryFactory.selectFrom(user)
.join(user.orders, order)
.where(order.amount.gt(100))
.fetch();

List<User> users = queryFactory.selectFrom(user)
.orderBy(user.name.asc())
.fetch();

List<User> users = queryFactory.selectFrom(user)
.groupBy(user.country)
.fetch();

long updatedCount = queryFactory.update(user)
.where(user.age.lt(18))
.set(user.status, UserStatus.INACTIVE)
.execute();

2.2 Key Methods in JPA Criteria

CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaQuery<User> cq = cb.createQuery(User.class);
Root<User> userRoot = cq.from(User.class);
cq.select(userRoot);

cq.where(cb.greaterThan(userRoot.get("age"), 18));

Join<User, Order> orderJoin = userRoot.join("orders");
cq.where(cb.greaterThan(orderJoin.get("amount"), 100));

cq.orderBy(cb.asc(userRoot.get("name")));

cq.groupBy(userRoot.get("country"));

CriteriaUpdate<User> update = cb.createCriteriaUpdate(User.class);
Root<User> userRoot = update.from(User.class);
update.set("status", UserStatus.INACTIVE)
.where(cb.lessThan(userRoot.get("age"), 18));
int updatedCount = entityManager.createQuery(update).executeUpdate();

3. Comparing Querydsl and JPA Criteria

Let’s compare Querydsl and JPA Criteria from various perspectives. The entity and DTO classes used in the examples below can be downloaded from the Downloads section. To set up the code examples for Querydsl and JPA Criteria, you’ll need to include the necessary dependencies in your project configuration file.

For Querydsl, include the following dependencies in your Maven configuration:

<dependency>
    <groupId>com.querydsl</groupId>
    <artifactId>querydsl-core</artifactId>
    <version>your_version</version>
</dependency>

<dependency>
    <groupId>com.querydsl</groupId>
    <artifactId>querydsl-jpa</artifactId>
    <version>your_version</version>
</dependency>

JPA Criteria is part of the Java Persistence API (JPA) and is typically included as part of the JPA provider dependency. Ensure you have the appropriate JPA provider dependency in your project configuration. For example, if you’re using Hibernate as your JPA provider, include the following dependency:

<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-core</artifactId>
    <version>your_version</version>
</dependency>

Additionally, make sure you have the JDBC driver dependency for your chosen database included in your project configuration. For the below examples, I have used PostgreSQL running on Docker.

3.1 Simple Queries

Both Querydsl and JPA Criteria can be used to construct simple queries. Let’s look at an example where we fetch all users from a database.

Querydsl

QUser user = QUser.user;
JPAQueryFactory queryFactory = new JPAQueryFactory(entityManager);
List<User> users = queryFactory.selectFrom(user).fetch();

In Querydsl, we use the QUser class, which is generated from our User entity. The JPAQueryFactory is used to create the query, and we fetch the results with fetch().

JPA Criteria

CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaQuery<User> cq = cb.createQuery(User.class);
Root<User> userRoot = cq.from(User.class);
cq.select(userRoot);
List<User> users = entityManager.createQuery(cq).getResultList();

With JPA Criteria, we first obtain a CriteriaBuilder from the EntityManager. We then create a CriteriaQuery, specify the root entity, and execute the query to fetch the results.

3.2 Filtering, Ordering, and Grouping

Let’s add filtering, ordering, and grouping to our queries.

Querydsl

List<User> users = queryFactory.selectFrom(user)
    .where(user.age.gt(18))
    .orderBy(user.name.asc())
    .groupBy(user.country)
    .fetch();

Querydsl provides a fluent API to chain filtering, ordering, and grouping clauses. Here, we filter users by age, order by name, and group by country.

JPA Criteria

cq.select(userRoot)
    .where(cb.greaterThan(userRoot.get("age"), 18))
    .orderBy(cb.asc(userRoot.get("name")))
    .groupBy(userRoot.get("country"));
List<User> users = entityManager.createQuery(cq).getResultList();

In JPA Criteria, we use the CriteriaBuilder to add filtering, ordering, and grouping clauses to our query.

3.3 Complex Queries With JOINs

Next, we’ll look at performing complex queries involving JOINs.

Querydsl

QOrder order = QOrder.order;
List<User> users = queryFactory.selectFrom(user)
    .join(user.orders, order)
    .where(order.amount.gt(100))
    .fetch();

In Querydsl, we use the join method to perform a JOIN operation. Here, we join the orders collection in the User entity and filter orders by amount.

JPA Criteria

Join<User, Order> orderJoin = userRoot.join("orders");
cq.select(userRoot)
    .where(cb.greaterThan(orderJoin.get("amount"), 100));
List<User> users = entityManager.createQuery(cq).getResultList();

In JPA Criteria, we use the join method on the Root to perform the join and then add the filtering condition.

3.4 Modifying Data

Both frameworks support updating and deleting records.

Querydsl

long updatedCount = queryFactory.update(user)
    .where(user.age.lt(18))
    .set(user.status, UserStatus.INACTIVE)
    .execute();

In Querydsl, the update method allows us to update records. Here, we update the status of users who are younger than 18.

JPA Criteria

CriteriaUpdate<User> update = cb.createCriteriaUpdate(User.class);
Root<User> userRoot = update.from(User.class);
update.set("status", UserStatus.INACTIVE)
    .where(cb.lessThan(userRoot.get("age"), 18));
int updatedCount = entityManager.createQuery(update).executeUpdate();

In JPA Criteria, we create a CriteriaUpdate object, set the update conditions, and execute the update.

3.5 Integration With Spring Data JPA

Both Querydsl and JPA Criteria can be integrated with Spring Data JPA.

Querydsl

public interface UserRepository extends JpaRepository<User, Long>, QuerydslPredicateExecutor<User> {
}

Spring Data JPA provides built-in support for Querydsl through the QuerydslPredicateExecutor interface. This allows us to use Querydsl predicates in repository methods.

JPA Criteria

public interface UserRepository extends JpaRepository<User, Long> {
    default List<User> findActiveUsers(EntityManager em) {
        CriteriaBuilder cb = em.getCriteriaBuilder();
        CriteriaQuery<User> cq = cb.createQuery(User.class);
        Root<User> userRoot = cq.from(User.class);
        cq.select(userRoot).where(cb.equal(userRoot.get("status"), UserStatus.ACTIVE));
        return em.createQuery(cq).getResultList();
    }
}

For JPA Criteria, we can define custom query methods directly in the repository implementation. Here, we fetch active users using a criteria query.

4. Performance Comparison of Querydsl and JPA Criteria

The performance of query frameworks can be influenced by several factors, including:

• Query construction time
• Query execution time
• Overhead associated with the framework
• Integration with other frameworks and libraries

4.1 Performance Comparison

QUser user = QUser.user;
List<User> users = queryFactory.selectFrom(user)
.where(user.age.gt(18))
.fetch();

CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaQuery<User> cq = cb.createQuery(User.class);
Root<User> userRoot = cq.from(User.class);
cq.select(userRoot)
.where(cb.greaterThan(userRoot.get("age"), 18));
List<User> users = entityManager.createQuery(cq).getResultList();

5. Conclusion

Choosing between Querydsl and JPA Criteria largely depends on your project requirements and personal preference. Querydsl’s fluent API and multi-backend support make it a popular choice for many developers, while JPA Criteria’s standardization and integration with JPA providers make it a reliable and consistent option.

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