3. Java Persistence API. 4. Java Persistence Query Language презентация

3. Java Persistence API 4. Java Persistence Query Language

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

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

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(); }

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; }}

MerchantServiceImpl Class @Named public class MerchantServiceImpl implements MerchantService{ @Inject private MerchantDao merchantDao; . . . . . . . . . . . . . public List<Merchant> findAll(){ return merchantDao.findAll(); } }

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()); }

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

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

Exercise: Find Payments Find all payments to the given merchant

DAO & Service Interfaces public interface PaymentDao { public List<Payment> findByMerchantId(int id); } public interface PaymentService { public List<Payment> findByMerchantId(int id); }

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(); } }

PaymentServiceImpl Class @Named public class PaymentServiceImpl implements PaymentService{ @Inject private PaymentDao paymentDao; public List<Payment> findByMerchantId(int id){ return paymentDao.findByMerchantId(id); } }

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()); }

Exercise: Find Payments See P342PaymentsWhere project for the full text

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

Join Example Get names of customers who payed more then 500.0 by the time

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); }

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(); }

CustomerServiceImpl Class public List<String> getNames(double sumPayed){ return customerDao.getNames(sumPayed); }

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); }

Join Example See P343PaymentJoin project for the full text

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.

Aggregate Example Find the sum of all payments

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(); }

PaymentDaoImpl Class public double getPaymentSum(){ TypedQuery<Double> query = em.createQuery ("SELECT SUM(p.sumPayed) FROM Payment p", Double.class); return query.getSingleResult(); }

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); }

Aggregate Example See P344Aggregation project for the full text

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

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); }

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(); }

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

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

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

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

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

Exercise: Sort Merchants Create a project to sort merchants by the value of needToSend field

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(); }

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(); }

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()); }

Exercise: Sort Merchants See P346Sort project for the full text

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

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

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

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.

Example: Grouping Payments Get general sum of charge for every merchant

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; } . . . . . . .

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(); }

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(); }

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()); }

Example: Grouping Payments See P347Grouping project for the full text