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 ProjectDependencies 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
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