Презентация 3. Java Persistence API. 4. Entity Relationships онлайн
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Слайды и текст к этой презентации:
№1 слайд
Содержание слайда: 3. Java Persistence API
4. Entity Relationships
№2 слайд
Содержание слайда: Basics
A foreign key can be one or more columns that reference a unique key, usually the primary key, in another table
A foreign key and the primary parent key it references must have the same number and type of fields
Foreign keys represents relationships from a column or columns in one table to a column or columns in another table
№3 слайд
Содержание слайда: Multiplicity in Entity Relationships
Multiplicities are of the following types:
Many-to-one: Multiple instances of an entity can be related to a single instance of the other entity
One-to-one: Each entity instance is related to a single instance of another entity
One-to-many: An entity instance can be related to multiple instances of the other entities
Many-to-many: The entity instances can be related to multiple instances of each other.
№4 слайд
Содержание слайда: CM Database Schema
№5 слайд
Содержание слайда: Many-to-One Mappings
A many-to-one mapping is defined by annotating the attribute in the source entity (the attribute that refers to the target entity) with the @ManyToOne annotation
A @JoinColumn(name=Fkname) annotation discribes a foreing key of a relationship
№6 слайд
Содержание слайда: Exercise: Read a Payment
Create a project for read payment data by payment id with a merchant name instead of merchant id
№7 слайд
Содержание слайда: CM Database Schema
№8 слайд
Содержание слайда: Payment Entity (1 of 2)
@Entity
public class Payment {
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private int id;
private double charge;
private double total;
private String goods;
private java.sql.Date dt;
@ManyToOne
@JoinColumn(name="merchantId")
private Merchant merchant;
№9 слайд
Содержание слайда: Payment Entity (2 of 2)
public Merchant getMerchant(){ return merchant; }
public void setMerchant(Merchant value){
merchant = value;
}
. . . . . . . . . . . . . . . .
public String getStringForPrint() {
String txt = "id = " + id + "; date = ";
SimpleDateFormat dtFrm = new SimpleDateFormat("dd.MM.yyyy");
txt += dtFrm.format(dt) + "; merchant = " + merchant.getName();
txt += "; total = " + total + "; charge = " + charge;
return txt;
}
№10 слайд
Содержание слайда: DAO & Service Interfaces
public interface PaymentDao {
public List<Payment> findByMerchantId(int id);
public double getPaymentSum();
public Payment findById(int id);
}
public interface PaymentService {
public List<Payment> findByMerchantId(int id);
public double getPaymentSum();
public Payment findById(int id);
}
№11 слайд
Содержание слайда: PaymentDaoImpl Class
public Payment findById(int id){
return em.find(Payment.class, id);
}
№12 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);
Payment p = paymentService.findById(2);
System.out.println(p.toString());
}
№13 слайд
Содержание слайда: Exercise: Read a Payment
See P351ReadPayment project for the full text
№14 слайд
Содержание слайда: Exercise: Group Payments
Modify P237Grouping project using entities from the previous project
№15 слайд
Содержание слайда: PaymentDaoImp Class
public List<Result> getTotalReport(){
String txt = "SELECT new com.bionic.edu.Result
(p.merchant.name, count(p), SUM(p.chargePayed))";
txt += "FROM Payment p GROUP BY p.merchant.name";
TypedQuery<Result> query = em.createQuery(txt, Result.class);
return query.getResultList();
}
№16 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<Result> list = paymentService.getTotalReport();
for(Result r: list)
System.out.format("%1$25s %2$3d %3$8.2f \n", r.getName(), r.getCount(), r.getSum());
}
№17 слайд
Содержание слайда: Exercise: Group Payments
See P352GroupPayment project for the full text
№18 слайд
Содержание слайда: One-to-Many Mappings
An entity instance can be related to multiple instances of the other entities
One-to-many relationships use the @OneToMany annotation on the corresponding persistent property or field
The mappedBy element is needed to refer to the attribute annotated by ManyToOne in the corresponding entity:
@OneToMany(mappedBy=“attribute”)
A one-to-many association needs to map the collection of entities
№19 слайд
Содержание слайда: Exercise: Read a Merchant’s Payments
Create a project for read payment data that correspond to a merchant given by its id
№20 слайд
Содержание слайда: CM Database Schema
№21 слайд
Содержание слайда: Merchant Entity
@Entity
public class Merchant {
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private int id;
private String name;
private double charge;
private int period;
private double total;
@OneToMany(mappedBy="merchant")
private Collection<Payment> payments;
№22 слайд
Содержание слайда: Main Class (1 of 2)
@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("=======================");
System.out.println(m.getName());
№23 слайд
Содержание слайда: Main Class (2 of 2)
System.out.println(" ");
Collection<Payment> payments = m.getPayments();
for (Payment p : payments) {
System.out.println(p.toString());
}
}
}
№24 слайд
Содержание слайда: Exercise: Read a Merchant’s Payments
See P353MerchantPayments project for the full text
№25 слайд
Содержание слайда: Many-to-Many Mappings
The entity instances can be related to multiple instances of each other
Many-to-many relationships use the @ManyToMany annotation on the corresponding persistent property or field
We must use a third table to associate the two entity types (join table)
№26 слайд
Содержание слайда: @JoinTable Annotation
@JoinTable(name=“table name”,
joinColumns=@JoinColumn(name=“c1Id”),
inverseJoinColumns=
@JoinColumn(name=“c2Id”))
№27 слайд
Содержание слайда: Exercise: Read Customer’s Merchants
Create a project to read data about merchants whose goods were bought by a given customer
№28 слайд
Содержание слайда: Customer Entity (1 of 2)
@Entity
public class Customer {
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private int id;
private java.sql.Date maturity;
private String ccType;
private String ccNo;
private String eMail;
private String address;
private String name;
№29 слайд
Содержание слайда: Customer Entity (2 of 2)
@ManyToMany
@JoinTable(name="Payment", joinColumns=@JoinColumn(name="customerId"),
inverseJoinColumns=@JoinColumn(name="merchantId"))
private Collection<Merchant> merchants;
№30 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);
Customer customer = customerService.findById(1);
if (customer != null){
System.out.println(customer.toString());
Collection<Merchant> merchants = customer.getMerchants();
for (Merchant m : merchants) { System.out.println(m.getName());}}}
№31 слайд
Содержание слайда: Exercise: Read Customer’s Merchants
See P354CustAndMerch project for the full text
№32 слайд
Содержание слайда: Lazy Relationships
The fetch mode can be specified on any of the four relationship mapping types:
@ManyToOne(fetch=FetchType.LAZY)
Lazy loading can essential enhance performance
№33 слайд
Содержание слайда: One-to-One Mappings
Each entity instance is related to a single instance of another entity
One-to-one relationships use the @OneToOne annotation on the corresponding persistent property or field
Example of One-To-One mapping: Employee and ParkingSpace entities
№34 слайд
Содержание слайда: Embedded Objects (1 of 2)
An embedded object is one that is dependent on an entity for its identity
It has no identity of its own, but is merely part of the entity state
The state of the embedded object is stored with the rest of the entity state in the database row, with no distinction between the state in the Java entity and that in its embedded object
№35 слайд
Содержание слайда: Embedded Objects (2 of 2)
We can share the same embedded object type with other entities that also have the same internal representation
Example: the home address of the employee (contains Street, City, State, ZipCode fields)
№36 слайд
Содержание слайда: Embedded Type
An embedded type is marked as such by adding the @Embeddable annotation to the class definition
Its fields and properties will be persistable as part of an entity
We might also want to define the access type of the embeddable object so it is accessed the same way regardless of which entity it is embedded in
№37 слайд
Содержание слайда: Address Embedded Type
@Embeddable
@Access(AccessType.FIELD)
public class Address {
private String street;
private String city;
private String state;
private String zipCode;
// ...
}
№38 слайд
Содержание слайда: Using an Embedded Object
@Entity
public class Employee {
@Id
private int id;
private String name;
private long salary;
@Embedded
private Address address;
// ...
}
№39 слайд
Содержание слайда: Reuse of Embedded Type
An Address class could be reused in both Employee and Company entities
№40 слайд
Содержание слайда: Database Schema Generation
Automatically generation the tables and database schema for a persistence unit can be done through the "eclipselink.ddl-generation" persistence unit property
The tables and constraints will be generated for all of the classes defined in that persistence unit.
№41 слайд
Содержание слайда: eclipselink.ddl-generation Values
create-tables – if the table already exists then it will not be dropped or replaced, the existing table will be used
drop-and-create-tables - will first drop the existing table, and then create the new table. Note that this will lose all of the data in the tables when they are dropped!!
№42 слайд
Содержание слайда: Schema Generation Practice
One of the complaints around schema generation is that you can’t specify everything that you need to be able to finely tune the schema.
There are too many differences between databases and too many different settings to try to put in options for every database type.
№43 слайд
Содержание слайда: Schema Generation Practice
If every database-tuning option were exposed through JPA then we would end up duplicating the features of Data Definition Language (DDL) in an API
The final schema will typically be tuned by a database administrator or someone with the appropriate level of database experience.
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