Презентация 3. Java Persistence API. 4. Java Persistence Query Language онлайн
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Слайды и текст к этой презентации:
№1 слайд
Содержание слайда: 3. Java Persistence API
4. Java Persistence Query Language
№2 слайд
Содержание слайда: Queries (1 of 2)
In JPA: SQL -> JP QL (Java Persistence Query Language)
A query is implemented in code as a Query or TypedQuery object. They are constructed using the EntityManager as a factory
A query can be customized according to the needs of the application
№3 слайд
Содержание слайда: Queries (2 of 2)
A query can be issued at runtime by supplying the JP QL query criteria, or a criteria object. Example:
TypedQuery<Merchant> query = em.createQuery("SELECT m FROM Merchant m", Merchant.class);
List<Merchant> listM = null;
listM = query.getResultList();
. . . . . . . . . . . .
See P341SelectMerchant project for the full text
№4 слайд
Содержание слайда: DAO & Service Interfaces
public interface MerchantDao {
public Merchant findById(int id);
public List<Merchant> findAll();
}
public interface MerchantService {
public Merchant findById(int id);
public List<Merchant> findAll();
}
№5 слайд
Содержание слайда: MerchantDaoImpl Class
@Repository
public class MerchantDaoImpl implements MerchantDao{
@PersistenceContext
private EntityManager em;
. . . . . . . . . . . .
public List<Merchant> findAll(){
TypedQuery<Merchant> query =
em.createQuery("SELECT m FROM Merchant m", Merchant.class);
List<Merchant> listM = null;
listM = query.getResultList();
return listM; }}
№6 слайд
Содержание слайда: MerchantServiceImpl Class
@Named
public class MerchantServiceImpl implements MerchantService{
@Inject
private MerchantDao merchantDao;
. . . . . . . . . . . . .
public List<Merchant> findAll(){
return merchantDao.findAll();
}
}
№7 слайд
Содержание слайда: Main Class
@SuppressWarnings("resource")
public static void main(String[] args) {
ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
MerchantService merchantService = context.getBean(MerchantService.class);
List<Merchant> list = merchantService.findAll();
for(Merchant m: list)
System.out.println("name = " + m.getName() + " charge = " +m.getCharge());
}
№8 слайд
Содержание слайда: Java Persistence Query Language
Java Persistence Query Language (JP QL) is a database-independent query language that operates on the logical entity model as opposed to the physical data model
Queries may also be expressed in SQL to take advantage of the underlying database
The key difference between SQL and JP QL is that instead of selecting from a table, an entity from the application domain model has been specified instead
№9 слайд
Содержание слайда: Filtering Results
JP QL supports the WHERE clause to set conditions on the data being returned
Majority of operators commonly available in SQL are available in JP QL:
basic comparison operators
IN expression
LIKE expression
BETWEEN expression
subqueries
№10 слайд
Содержание слайда: Exercise: Find Payments
Find all payments to the given merchant
№11 слайд
Содержание слайда: DAO & Service Interfaces
public interface PaymentDao {
public List<Payment> findByMerchantId(int id);
}
public interface PaymentService {
public List<Payment> findByMerchantId(int id);
}
№12 слайд
Содержание слайда: PaymentDaoImpl Class
@Repository
public class PaymentDaoImpl implements PaymentDao{
@PersistenceContext
private EntityManager em;
public List<Payment> findByMerchantId(int id){
TypedQuery<Payment> query = em.createQuery("SELECT p FROM Payment p WHERE p.merchantId = " + id, Payment.class);
return query.getResultList();
}
}
№13 слайд
Содержание слайда: PaymentServiceImpl Class
@Named
public class PaymentServiceImpl implements PaymentService{
@Inject
private PaymentDao paymentDao;
public List<Payment> findByMerchantId(int id){
return paymentDao.findByMerchantId(id);
}
}
№14 слайд
Содержание слайда: Main Class
@SuppressWarnings("resource")
public static void main(String[] args) {
ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
PaymentService paymentService = context.getBean(PaymentService.class);
List<Payment> list = paymentService.findByMerchantId(3);
for(Payment p: list)
System.out.println(p.toString());
}
№15 слайд
Содержание слайда: Exercise: Find Payments
See P342PaymentsWhere project for the full text
№16 слайд
Содержание слайда: Joins Between Entities
Just as with SQL and tables, if we want to navigate along a collection association and return elements of that collection, we must join the two entities together
In JP QL, joins may also be expressed in the FROM clause using the JOIN operator
№17 слайд
Содержание слайда: Join Example
Get names of customers who payed more then 500.0 by the time
№18 слайд
Содержание слайда: DAO & Service Interfaces
public interface CustomerDao {
public Customer findById(int id);
. . . . . . . . . . . . . .
public List<String> getNames(double sumPayed);
}
public interface CustomerService {
public Customer findById(int id);
. . . . . . . . . . . . . .
public List<String> getNames(double sumPayed);
}
№19 слайд
Содержание слайда: CustomerDaoImpl Class
public List<String> getNames(double sumPayed){
String txt = "SELECT DISTINCT c.name FROM ";
txt += "Payment p, Customer c " ;
txt += "WHERE c.id = p.customerId AND p.sumPayed > " + sumPayed;
TypedQuery<String> query = em.createQuery(txt, String.class);
return query.getResultList();
}
№20 слайд
Содержание слайда: CustomerServiceImpl Class
public List<String> getNames(double sumPayed){
return customerDao.getNames(sumPayed);
}
№21 слайд
Содержание слайда: Main Class
@SuppressWarnings("resource")
public static void main(String[] args) {
ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
CustomerService customerService = context.getBean(CustomerService.class);
List<String> list = customerService.getNames(500.0);
for(String s: list)
System.out.println(s);
}
№22 слайд
Содержание слайда: Join Example
See P343PaymentJoin project for the full text
№23 слайд
Содержание слайда: Aggregate Queries
There are five supported aggregate functions (AVG, COUNT, MIN, MAX, SUM)
Results may be grouped in the GROUP BY clause and filtered using the HAVING clause.
№24 слайд
Содержание слайда: Aggregate Example
Find the sum of all payments
№25 слайд
Содержание слайда: DAO & Service Interfaces
public interface PaymentDao {
public List<Payment> findByMerchantId(int id);
public double getPaymentSum();
}
public interface PaymentService {
public List<Payment> findByMerchantId(int id);
public double getPaymentSum();
}
№26 слайд
Содержание слайда: PaymentDaoImpl Class
public double getPaymentSum(){
TypedQuery<Double> query = em.createQuery ("SELECT SUM(p.sumPayed) FROM Payment p", Double.class);
return query.getSingleResult();
}
№27 слайд
Содержание слайда: Main Class
@SuppressWarnings("resource")
public static void main(String[] args) {
ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
PaymentService paymentService = context.getBean(PaymentService.class);
double sum = paymentService.getPaymentSum();
System.out.println("total = " + sum);
}
№28 слайд
Содержание слайда: Aggregate Example
See P344Aggregation project for the full text
№29 слайд
Содержание слайда: Query Positional Parameters
Parameters are indicated in the query string by a question mark followed by the parameter number
When the query is executed, the developer specifies the parameter number that should be replaced
№30 слайд
Содержание слайда: DAO & Service Interfaces
public interface PaymentDao {
public List<Payment> findByMerchantId(int id);
public double getPaymentSum();
public List<Payment> getLargePayments(double limit);
}
public interface PaymentService {
public List<Payment> findByMerchantId(int id);
public double getPaymentSum();
public List<Payment> getLargePayments(double limit);
}
№31 слайд
Содержание слайда: PaymentDaoImpl Class
public List<Payment> getLargePayments(double limit){
TypedQuery<Payment> query = em.createQuery ("SELECT p FROM Payment p WHERE p.sumPayed > ?1", Payment.class);
query.setParameter(1, limit);
return query.getResultList();
}
№32 слайд
Содержание слайда: Main Class
@SuppressWarnings("resource")
public static void main(String[] args) {
ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
PaymentService paymentService = context.getBean(PaymentService.class);
List<Payment> list = paymentService.getLargePayments(750.0);
for (Payment p: list)
System.out.println(p.toString());
}
See P345Parameters project for the full text
№33 слайд
Содержание слайда: Query Named Parameters
Named parameters may also be used and are indicated in the query string by a colon followed by the parameter name
When the query is executed, the developer specifies the parameter name that should be replaced
№34 слайд
Содержание слайда: PaymentDaoImpl Class
public List<Payment> getLargePayments(double limit){
TypedQuery<Payment> query = em.createQuery ("SELECT p FROM Payment p WHERE p.sumPayed > :limit", Payment.class);
query.setParameter("limit", limit);
return query.getResultList();
}
See P245Parameters project for the full text
№35 слайд
Содержание слайда: Executing Queries
The TypedQuery interface provides three different ways to execute a query:
getSingleResult() - if the query is expected to return a single result
getResultList() - if more than one result may be returned
executeUpdate() - is used to invoke bulk update and delete queries
№36 слайд
Содержание слайда: getResultList() Method
Returns a collection containing the query results
If the query did not return any data, the collection is empty
The return type is specified as a List instead of a Collection in order to support queries that specify a sort order
If the query uses the ORDER BY clause to specify a sort order, the results will be put into the result list in the same order
№37 слайд
Содержание слайда: Exercise: Sort Merchants
Create a project to sort merchants by the value of needToSend field
№38 слайд
Содержание слайда: DAO & Service Interfaces
public interface MerchantDao {
public Merchant findById(int id);
public List<Merchant> getSortedByNeedToPay();
}
public interface MerchantService {
public Merchant findById(int id);
public List<Merchant> getSortedByNeedToPay();
}
№39 слайд
Содержание слайда: MerchantDaoImpl Class
public List<Merchant> getSortedByNeedToPay(){
String txt = "SELECT m FROM Merchant m ORDER BY m.needToSend";
TypedQuery<Merchant> query = em.createQuery(txt, Merchant.class);
return query.getResultList();
}
№40 слайд
Содержание слайда: Main Class
@SuppressWarnings("resource")
public static void main(String[] args) {
ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
MerchantService merchantService = context.getBean(MerchantService.class);
List<Merchant> list = merchantService.getSortedByNeedToPay();
for(Merchant m: list)
System.out.println("name = " + m.getName() + " sumToPay = " + m .getNeedToSend());
}
№41 слайд
Содержание слайда: Exercise: Sort Merchants
See P346Sort project for the full text
№42 слайд
Содержание слайда: getSingleResult() Method
Instead of iterating to the first result in a collection, the object is directly returned
Throws a NoResultException exception when no results are available
Throws a NonUniqueResultException exception if multiple results are available after executing the query
№43 слайд
Содержание слайда: Working with Query Results
The result type of a query is determined by the expressions listed in the SELECT clause of the query:
Basic types, such as String, the primitive types, and JDBC types
Entity types
An array of Object
User-defined types created from a constructor expression
№44 слайд
Содержание слайда: Constructor expressions (1/2)
Provide developers with a way to map array of Object result types to custom objects
Typically this is used to convert the results into JavaBean-style classes that provide getters for the different returned values
A constructor expression is defined in JP QL using the NEW operator in the SELECT clause
№45 слайд
Содержание слайда: Constructor expressions (2/2)
The argument to the NEW operator is the fully qualified name of the class that will be instantiated to hold the results for each row of data returned
The only requirement on this class is that it has a constructor with arguments matching the exact type and order that will be specified in the query.
№46 слайд
Содержание слайда: Example: Grouping Payments
Get general sum of charge for every merchant
№47 слайд
Содержание слайда: Class Result
public class Result {
private String name;
private double sum;
public Result(){ }
public Result(String name, double sum){
this.name = name;
this.sum = sum;
}
public String getName() { return name; }
. . . . . . .
№48 слайд
Содержание слайда: DAO & Service Interfaces
public interface MerchantDao {
public Merchant findById(int id);
public List<Merchant> getSortedByNeedToPay();
public List<Result> getTotalReport();
}
public interface MerchantService {
public Merchant findById(int id);
public List<Merchant> getSortedByNeedToPay();
public List<Result> getTotalReport();
}
№49 слайд
Содержание слайда: MerchantDaoImpl Class
public List<Result> getTotalReport(){
String txt = "SELECT new com.bionic.edu.Result (m.name, SUM(p.chargePayed)) ";
txt += "FROM Payment p, Merchant m WHERE m.id = p.merchantId GROUP BY m.name";
TypedQuery<Result> query = em.createQuery(txt, Result.class);
return query.getResultList();
}
№50 слайд
Содержание слайда: Main Class
@SuppressWarnings("resource")
public static void main(String[] args) {
ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
MerchantService merchantService = context.getBean(MerchantService.class);
List<Result> list = merchantService.getTotalReport();
for(Result r: list)
System.out.format("%1$25s %2$8.2f \n", r.getName(), r.getSum());
}
№51 слайд
Содержание слайда: Example: Grouping Payments
See P347Grouping project for the full text
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