A ParameterExpression (extends Expression) represents a query parameter whose value is provided at the time when query is executed.

Following two methods are defined in CriteriaBuilder to create an instance of ParameterExpression:

ParameterExpression<T> parameter(Class<T> paramClass);

Quick example:

  CriteriaBuilder cb = entityManager.getCriteriaBuilder();
  //query creation
  CriteriaQuery<Employee> query = cb.createQuery(Employee.class);
  Root<Employee> employee = query.from(Employee.class);
  ParameterExpression<String> parameterExpression = cb.parameter(String.class);
  query.select(employee)
       .where(cb.equal(employee.get(Employee_.name), parameterExpression));
  //query execution 
  TypedQuery<Employee> typedQuery = entityManager.createQuery(query);
  typedQuery.setParameter(parameterExpression, "Diana");
  List<Employee> resultList = typedQuery.getResultList();

Following method is used to create a named parameter.

ParameterExpression<T> parameter(Class<T> paramClass, String name);

Quick example:

  //query execution
  CriteriaBuilder cb = entityManager.getCriteriaBuilder();
  CriteriaQuery<Employee> query = cb.createQuery(Employee.class);
  Root<Employee> employee = query.from(Employee.class);
  query.select(employee)
       .where(cb.equal(employee.get(Employee_.name), cb.parameter(String.class, "empName")));
  //query execution
  TypedQuery<Employee> typedQuery = entityManager.createQuery(query);
  typedQuery.setParameter("empName", "Diana");
  List<Employee> resultList = typedQuery.getResultList();

Example

Entity

@Entity
public class Employee {
    @Id
    @GeneratedValue
    private long id;
    private String name;
    private double salary;
    private String dept;
    .............
}

Using ParameterExpression

public class ExampleMain {
    private static EntityManagerFactory entityManagerFactory =
            Persistence.createEntityManagerFactory("example-unit");

    public static void main(String[] args) {
        try {
            persistEmployees();
            findAllEmployeeEntities();
            findEmployeeBySalaries();
            findEmployeeByDept();
        } finally {
            entityManagerFactory.close();
        }
    }

    public static void persistEmployees() {
        Employee employee1 = Employee.create("Diana", 2000, "IT");
        Employee employee2 = Employee.create("Rose", 4500, "Admin");
        Employee employee3 = Employee.create("Denise", 2000, "Admin");
        Employee employee4 = Employee.create("Mike", 4000, "IT");
        Employee employee5 = Employee.create("Linda", 4500, "Sales");
        EntityManager em = entityManagerFactory.createEntityManager();
        em.getTransaction().begin();
        em.persist(employee1);
        em.persist(employee2);
        em.persist(employee3);
        em.persist(employee4);
        em.persist(employee5);
        em.getTransaction().commit();
        em.close();
    }

    private static void findAllEmployeeEntities() {
        System.out.println("-- finding Employee entities - entity selection --");
        EntityManager em = entityManagerFactory.createEntityManager();
        CriteriaBuilder cb = em.getCriteriaBuilder();
        CriteriaQuery<Employee> query = cb.createQuery(Employee.class);
        Root<Employee> employee = query.from(Employee.class);
        query.select(employee);
        TypedQuery<Employee> typedQuery = em.createQuery(query);
        List<Employee> resultList = typedQuery.getResultList();
        resultList.forEach(System.out::println);
        em.close();
    }

    private static void findEmployeeBySalaries() {
        System.out.println("-- Employee with salaries greater than 2000 --");
        EntityManager em = entityManagerFactory.createEntityManager();
        CriteriaBuilder cb = em.getCriteriaBuilder();
        CriteriaQuery<Employee> query = cb.createQuery(Employee.class);
        Root<Employee> employee = query.from(Employee.class);
        ParameterExpression<Double> parameterExpression = cb.parameter(Double.class);
        query.select(employee)
             .where(cb.gt(employee.get(Employee_.salary), parameterExpression));
        TypedQuery<Employee> typedQuery = em.createQuery(query);
        typedQuery.setParameter(parameterExpression, Double.valueOf(2000));
        List<Employee> resultList = typedQuery.getResultList();
        resultList.forEach(System.out::println);
        em.close();
    }

    private static void findEmployeeByDept() {
        System.out.println("-- Employee in IT dept --");
        EntityManager em = entityManagerFactory.createEntityManager();
        CriteriaBuilder cb = em.getCriteriaBuilder();
        CriteriaQuery<Employee> query = cb.createQuery(Employee.class);
        Root<Employee> employee = query.from(Employee.class);
        ParameterExpression<String> parameterExpression = cb.parameter(String.class, "dept");
        query.select(employee)
             .where(cb.equal(employee.get(Employee_.dept), parameterExpression));
        TypedQuery<Employee> typedQuery = em.createQuery(query);
        typedQuery.setParameter("dept", "IT");
        List<Employee> resultList = typedQuery.getResultList();
        resultList.forEach(System.out::println);
        em.close();
    }
}

-- finding Employee entities - entity selection --
Employee{id=1, name='Diana', salary=2000.0, dept='IT'}
Employee{id=2, name='Rose', salary=4500.0, dept='Admin'}
Employee{id=3, name='Denise', salary=2000.0, dept='Admin'}
Employee{id=4, name='Mike', salary=4000.0, dept='IT'}
Employee{id=5, name='Linda', salary=4500.0, dept='Sales'}
-- Employee with salaries greater than 2000 --
Employee{id=2, name='Rose', salary=4500.0, dept='Admin'}
Employee{id=4, name='Mike', salary=4000.0, dept='IT'}
Employee{id=5, name='Linda', salary=4500.0, dept='Sales'}
-- Employee in IT dept --
Employee{id=1, name='Diana', salary=2000.0, dept='IT'}
Employee{id=4, name='Mike', salary=4000.0, dept='IT'}

Example Project

Dependencies and Technologies Used:

• h2 1.4.197: H2 Database Engine.
• hibernate-core 5.3.5.Final: Hibernate's core ORM functionality.
  Implements javax.persistence:javax.persistence-api version 2.2
• hibernate-jpamodelgen 5.3.5.Final: Annotation Processor to generate JPA 2 static metamodel classes.
• JDK 1.8
• Maven 3.5.4