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1. Overview

In this tutorial, we’ll discuss a very useful JPA feature – Criteria Queries.

It not only enables us to write queries without doing raw SQL, but also gives us some Object Oriented control over the queries, which is one of the main features of Hibernate. The Criteria API allows us to build up a criteria query object programmatically, where we can apply different kind of filtration rules and logical conditions.

Since Hibernate 5.2, the Hibernate Criteria API is deprecated and new development is focused on the JPA Criteria API. We’ll explore how to use Hibernate and JPA to build Criteria Queries.

2. Maven Dependencies

To illustrate the API, we’ll use the reference JPA implementation – Hibernate.

To use Hibernate make sure you add the latest version of it to your pom.xml file:

<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-core</artifactId>   
    <version>5.3.2.Final</version>
</dependency>

The latest version of Hibernate can be found here.

3. Simple Example Using Criteria

Let’s start by looking at how to retrieve data using Criteria queries. We’ll have a look at how to get all the instances of a particular class from the database.

We have an Item class which represents the tuple “ITEM” in the database:

public class Item implements Serializable {

    private Integer itemId;
    private String itemName;
    private String itemDescription;
    private Integer itemPrice;

   // standard setters and getters
}

Let’s look at a simple criteria query which will retrieve all the rows of “ITEM” from the database:

Session session = HibernateUtil.getHibernateSession();
CriteriaBuilder cb = session.getCriteriaBuilder();
CriteriaQuery<Item> cr = cb.createQuery(Item.class);
Root<Item> root = cr.from(Item.class);
cr.select(root);

Query<Item> query = session.createQuery(cr);
List<Item> results = query.getResultList();

The above query is a simple demonstration of how to get all the items. Let’s see what was done, step by step:

  1. Create an instance of Session from the SessionFactory object
  2. Create an instance of CriteriaBuilder by calling the getCriteriaBuilder() method
  3. Create an instance of CriteriaQuery by calling the CriteriaBuilder createQuery() method
  4. Create an instance of Query by calling the Session createQuery() method
  5. Call the getResultList() method of the query object which gives us the results

Now that we’ve covered the basics, let’s move on to some of the features of criteria query:

3.1. Using Expressions

The CriteriaBuilder can be used to restrict query results based on specific conditions. By using CriteriaQuery where() method and provide Expressions created by CriteriaBuilder.

Here’re some examples of commonly used Expressions:

To get items having a price more than 1000:

cr.select(root).where(cb.gt(root.get("itemPrice"), 1000));

Next, getting items having itemPrice less than 1000:

cr.select(root).where(cb.lt(root.get("itemPrice"), 1000));

Items having itemNames contain Chair:

cr.select(root).where(cb.like(root.get("itemName"), "%chair%"));

Records having itemPrice in between 100 and 200:

cr.select(root).where(cb.between(root.get("itemPrice"), 100, 200));

To check if the given property is null:

cr.select(root).where(cb.isNull(root.get("itemDescription")));

To check if the given property is not null:

cr.select(root).where(cb.isNotNull(root.get("itemDescription")));

You can also use the methods isEmpty() and isNotEmpty() to test if a List within a class is empty or not.

Now inevitably the question comes, whether we can combine two or more of the above comparisons or not. The answer is, of course, yes – the Criteria API allows us to easily chain expressions:

Predicate[] predicates = new Predicate[2];
predicates[0] = cb.isNull(root.get("itemDescription"));
predicates[1] = cb.like(root.get("itemName"), "chair%");
cr.select(root).where(predicates);

To add two expressions with logical operations:

Predicate greaterThanPrice = cb.gt(root.get("itemPrice"), 1000);
Predicate chairItems = cb.like(root.get("itemName"), "Chair%");

Items with the above-defined conditions joined with Logical OR:

cr.select(root).where(cb.or(greaterThanPrice, chairItems));

To get items matching with the above-defined conditions joined with Logical AND:

cr.select(root).where(cb.and(greaterThanPrice, chairItems));

3.2. Sorting

Now that we know the basic usage of Criteria, let’s have a look at the sorting functionalities of Criteria.

In the following example we order the list in an ascending order of the name and then in a descending order of the price:

cr.orderBy(
  cb.asc(root.get("itemName")), 
  cb.desc(root.get("itemPrice")));

In the next section, we will have a look at how to do aggregate functions.

3.3. Projections, Aggregates And Grouping Functions

So far we have covered most of the basic topics. Now let’s have a look at the different aggregate functions:

Get row count:

CriteriaQuery<Long> cr = cb.createQuery(Long.class);
Root<Item> root = cr.from(Item.class);
cr.select(cb.count(root));
Query<Long> query = session.createQuery(cr);
List<Long> itemProjected = query.getResultList();

The following is an example of aggregate functions:

Aggregate function for Average:

CriteriaQuery<Double> cr = cb.createQuery(Double.class);
Root<Item> root = cr.from(Item.class);
cr.select(cb.avg(root.get("itemPrice")));
Query<Double> query = session.createQuery(cr);
List avgItemPriceList = query.getResultList();

Other useful aggregate methods that are available are sum(), max(), min() , count() etc.

4. Advantage Over HQL

In the previous sections we’ve covered how to use Criteria Queries.

Clearly, the main and most hard-hitting advantage of Criteria queries over HQL is the nice, clean, Object Oriented API.

We can simply write more flexible, dynamic queries compared to plain HQL. The logic can be refactored with the IDE and has all the type-safety benefits of the Java language itself.

There are of course some disadvantages as well, especially around more complex joins.

So, generally speaking, we’ll have to use the best tool for the job – that can be the Criteria API in most cases, but there are definitely cases where we’ll have to go lower level.

5. Conclusion

In this article, we focused on the basics of Criteria Queries in Hibernate and JPA, and also on some of the advanced features of the API.

The code discussed here is available in the Github repository.

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