2014 pre-msc-is-3 persistence layer

Andreas Martin -

Master of Science in Business Information Systems FHNW Pre-Master Information Systems

3. Persistence Layer

Andreas Martin


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Persistence Layer

Object- Relational Mapping (ORM)

Java Persistence API (JPA)

Java Transaction API (JTA)

Hands-on:

Hands-on 1: JAVA PERSISTENCE

Hands-on 2: MANAGING PERSISTENT OBJECTS


The Latte Macchiato «Layering» Principle

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Presentation Layer

Goal: Display of information, processing / forwarding of user interactions. Technologies: JavaServer Faces (JSF), JavaServer Pages (JSP), Servlets, etc.

Business (Logic) Layer

Goal: Reproduction of actions or «verbs» of the application (buy a book, print an order, deliver a book, etc.). Technologies: Enterprise Java Beans (EJBs)

Persistence Layer

Goal: Reproduction of database attributes, information or «nouns» in object / class attributes (Object-Relational Mapping, ORM). Technologies: Java Persistence API (JPA)


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JPA Specification at a Glance

ORM: Mapping of java objects and database relations.

Entity manager API: Database operations like: Create, Read, Update, Delete (CRUD).

Java Persistence Query Language (JPQL): Object oriented query language.

Java Transaction API (JTA): Transaction mechanism.


Source: Goncalves, 2010: Beginning Java™ EE 6 Platform with GlassFish™ 3 – Code (Apache-2.0 license): http://kenai.com/projects/beginningee6/

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Object-Relational Mapping (ORM)


Adapted from: Goncalves: Code and Models licensed under a CC BY-SA 3.0 License from https://github.com/agoncal/agoncal-book-javaee7

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Object-Relational Mapping (ORM)

@Entity: declares a database relation.

@Id: defines the primary key value(s).

@GeneratedValue: defines a value the will be automatically generated.

@Column: can be used to modify the standard mapping behaviour.


Listing: A Simple Book Entity @Entity public class Book { @Id @GeneratedValue private Long id; @Column(nullable = false) private String title; private Float price; @Column(length = 2000) private String description; private String isbn; private Integer nbOfPage; private Boolean illustrations; // Constructors, getters, setters }


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Simple Example of a Book Entity


Listing: Simple Example of a Book Entity @Entity public class Book { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; private String title; private Float price; private String description; private String isbn; private Integer nbOfPage; private Boolean illustrations; public Book() { } // Getters, setters }


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Simple Example of a Book Entity


Listing: Simple Example of a Book Entity

@Entity

public class Book {

@Id

@GeneratedValue(strategy =

GenerationType.AUTO)

private Long id;

private String title;

private Float price;

private String description;

private String isbn;

private Integer nbOfPage;

private Boolean illustrations;

public Book() {

}

// Getters, setters

}

Listing: Structure of the BOOK Table CREATE TABLE BOOK ( ID BIGINT NOT NULL, TITLE VARCHAR(255), PRICE DOUBLE(52, 0), DESCRIPTION VARCHAR(255), ISBN VARCHAR(255), NBOFPAGE INTEGER, ILLUSTRATIONS SMALLINT, PRIMARY KEY (ID) );


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Querying Entities using JPQL and EntityManager


EntityManagerFactory emf = Persistence.createEntityManagerFactory("primary");

EntityManager em = emf.createEntityManager();

em.persist(book);

The methods persist() and find() will be transferred by the EntityManager into JDBC calls (INSERT or SELECT SQL statements).


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Listing: A findBookByTitle Named Query @Entity @NamedQuery(name = "findBookWithTitleJava", query = "SELECT b FROM Book b WHERE b.title =‘Java'") public class Book { @Id @GeneratedValue private Long id; @Column(nullable = false) private String title; private Float price; @Column(length = 2000) private String description; private String isbn; private Integer nbOfPage; private Boolean illustrations; // Constructors, getters, setters }

Querying Entities using JPQL and EntityManager

Instead of using native SQL, it is more sophisticated to use JPQL:

SELECT b FROM Book b WHERE b.title = ‘Java‘;

JPQL is similar to SQL, which adds the object-point notation.



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Hands-on-1 Java Persistence


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Predefined Projects - Hands-on Projects @ GitHub …will be used for all the hands-on’s

1. First download “Hands-on Projects @ GitHub” ZIP- file from Moodle and extract it into a folder.

2. Import predefined projects in Eclipse:


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Database Connection …will be used for the next two hands-on’s

Create or modify the persistence.xml file:

Choose another student ‘number’ to avoid overwriting.


<?xml version="1.0" encoding="UTF-8"?>

<persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence

http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">

<persistence-unit name="primary" transaction-type="RESOURCE_LOCAL">

<provider>org.hibernate.ejb.HibernatePersistence</provider>

<properties>

<property name="hibernate.connection.username" value="premscis"/>

<property name="hibernate.connection.password" value="premscis"/>

<property name="hibernate.connection.url" value="jdbc:mysql://mature.iwi.wirtschaft.fhnw.ch:80/student0"/>

<property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver"/>

<property name="hibernate.cache.provider_class" value="org.hibernate.cache.NoCacheProvider"/>

<property name="hibernate.hbm2ddl.auto" value="update"/>

</properties>

</persistence-unit>

</persistence>

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Hands-on 1: Overview

Now we know what an entity or the entity manager is.

In this hands-on we are going to write a small application, which stores an entity into a database.

Create a Book entity and a Main class including a main method, that stores a book entry into our MySQL database (use the premscis scheme).

Use the predefined maven project and watch out the pre-configurations.


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Hands-on 1

1. Import (or create from blueprint) the hands-on-1 project. All the source code will be placed into the ch.fhnw.mscbis.premscis.handson1 package.

2. Create a Book entity with the following attributes: id, title, price, description, isbn, numberOfPages and illustrations. Choose the right datatypes.

3. Generate Getter & Setter methods.


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Hands-on 1

4. Create a Main class and a main method where you create a book.


// Create a book EntityManagerFactory emf = Persistence.createEntityManagerFactory("primary"); EntityManager em = emf.createEntityManager(); EntityTransaction tx = em.getTransaction(); tx.begin(); em.persist(book); tx.commit(); em.close(); emf.close();


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@Annotations

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@Table

@Table(name = ""): is used to define the name of the database table.

Btw.: @javax.persistence.Table would be the full path to the annotation, we can use the short form in combination with an include.


Listing: The Book Entity Being

Mapped to a T_BOOK Table

@Entity

@Table(name = "t_book")

public class Book {

@Id

private Long id;


private Float price;

private String description;

private String isbn;

private Integer nbOfPage;

private Boolean illustrations;

public Book() {

}

// Getters and setters

}


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@SecondaryTable



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@SecondaryTable


Listing: Attributes of the Address Entity Mapped in Three Different Tables @Entity @SecondaryTables( { @SecondaryTable(name = "city"), @SecondaryTable(name = "country") }) public class Address { @Id private Long id; private String street1; private String street2; @Column(table = "city") private String city; @Column(table = "city") private String state; @Column(table = "city") private String zipcode; @Column(table = "country") private String country; // Constructors, getters, setters }


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Composite Primary Key using @EmbeddedId


Listing: DDL of the NEWS Table with a Composite Primary Key create table NEWS ( CONTENT VARCHAR(255), TITLE VARCHAR(255) not null, LANGUAGE VARCHAR(255) not null, primary key (TITLE, LANGUAGE) );

Listing: The Entity Embeds the Primary Key Class with @EmbeddedId @Entity public class News { @EmbeddedId private NewsId id; private String content; // … }

Listing: The Primary Key Class Is

Annotated with @Embeddable

@Embeddable

public class NewsId {


private String language;

// …

}


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Relationship Mapping



Annotation Direction

@OneToOne Unidirectional

@OneToOne Bidirectional

@OneToMany Unidirectional

@ManyToOne / @OneToMany Bidirectional

@ManyToOne Unidirectional

@ManyToMany Unidirectional

@ManyToMany Bidirectional

All possible mappings:

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@OneToOne



Listing: The Customer Entity @Entity public class Customer { @Id @GeneratedValue private Long id; private String firstName; private String lastName; private String email; private String phoneNumber; @OneToOne @JoinColumn(name = "address_fk") private Address address; // Constructors, getters, setters } Listing: An Address Entity @Entity public class Address { @Id @GeneratedValue private Long id; private String street1; private String street2; private String city; private String state; private String zipcode; private String country; @OneToOne(mappedBy = "address") private Customer customer; // Constructors, getters, setters }

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@OneToMany Unidirectional


Listing: The Order Entity with a Join Column @Entity public class Order { @Id @GeneratedValue private Long id; @Temporal(TemporalType.TIMESTAMP) private Date creationDate; @OneToMany(fetch = FetchType.EAGER) @JoinColumn(name = "order_fk") private List<OrderLine> orderLines; // Constructors, getters, setters }

Listing: An OrderLine @Entity @Table(name = "order_line") public class OrderLine { @Id @GeneratedValue private Long id; private String item; private Double unitPrice; private Integer quantity; // Constructors, getters, setters }


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@ManyToMany Bidirectional – read & write


Listing: One Artist Appears on Several CD Albums @Entity public class Artist { @Id @GeneratedValue private Long id; private String firstName; private String lastName; @ManyToMany(cascade = CascadeType.ALL) @JoinTable(name = "jnd_art_cd", joinColumns = @JoinColumn(name = "artist_fk"), inverseJoinColumns = @JoinColumn(name = "cd_fk")) private List<CD> appearsOnCDs; // Constructors, getters, setters }

Listing: One CD is Created by Several Artists @Entity public class CD { @Id @GeneratedValue private Long id; private String title; private Float price; private String description; @ManyToMany(cascade = CascadeType.ALL) @JoinTable(name = "jnd_art_cd", joinColumns = @JoinColumn(name = "cd_fk"), inverseJoinColumns = @JoinColumn(name = "artist_fk")) private List<Artist> createdByArtists; // Constructors, getters, setters }


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Managing Persistent Objects


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Recap our Hands-on 1


Listing: A Main Class Persisting and Retrieving a Book Entity public class Main { public static void main(String[] args) { // 1-Create an instance of the Book entity Book book = new Book(); book.setId(1234L); book.setTitle("The Hitchhiker's Guide to the Galaxy"); book.setPrice(12.5F); book.setDescription("Science fiction created by Douglas Adams."); book.setIsbn("1-84023-742-2"); book.setNbOfPage(354); book.setIllustrations(false); // 2-Get an entity manager and a transaction EntityManagerFactory emf = Persistence.createEntityManagerFactory(«primary"); EntityManager em = emf.createEntityManager(); EntityTransaction tx = em.getTransaction(); // 3-Persist the book to the database tx.begin(); em.persist(book); tx.commit(); // 4-Retrieve the book by its identifier book = em.find(Book.class, 1234L); System.out.println(book); em.close(); emf.close(); } }


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Persisting an Entity


Listing: Persisting a Customer with an Address EntityManager em = …; Customer customer = new Customer("Antony", "Balla", "[email protected]"); Address address = new Address("Ritherdon Rd", "London", "8QE", "UK"); customer.setAddress(address); tx.begin(); em.persist(customer); em.persist(address); tx.commit(); assertNotNull(customer.getId()); assertNotNull(address.getId());


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JPQL


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UPDATE <entity name> [[AS] <identification variable>]

SET <update statement> {, <update statement>}*

[WHERE <conditional expression>]

DELETE FROM <entity name> [[AS] <identification var.>]


JPQL

SELECT- Syntax

DELETE- Syntax

UPDATE- Syntax

The JPQL syntax is comparable to the SQL syntax is used in a MySQL or Apache Derby environment.

Extensions in JPQL e.g.:


Source: Goncalves, 2010: Beginning Java™ EE 6 Platform with GlassFish™ 3 – Code (Apache-2.0 license): http://kenai.com/projects/beginningee6/

SELECT <expression>

FROM <clause>


[ORDER BY <clause>]

[GROUP BY <clause>]

[HAVING <clause>]

SELECT CASE b.author WHEN 'Martin'

THEN b.price * 1.5

ELSE b.price * 0.8

END

FROM Book b

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Named Queries

Named Queries like Dynamic Queries: Query query = em.createNamedQuery("findAll"); List<Customer> customers = query.getResultList();

as Named Typed Query: TypedQuery<Customer> query = em.createNamedQuery("findAll", Customer.class); List<Customer> customers = query.getResultList();

and including parameters Query query = em.createNamedQuery("findWithParam"); query.setParameter("fname", "Vincent"); List<Customer> customers = query.getResultList();


Listing: The Customer Entity Defining Named Queries @Entity @NamedQueries( { @NamedQuery(name = "findAll", query="select c from Customer c"), @NamedQuery(name = "findVincent", query="select c from Customer c where c.firstName = 'Vincent'"), @NamedQuery(name = "findWithParam", query="select c from Customer c where c.firstName = :fname") }) public class Customer { @Id @GeneratedValue private Long id; private String firstName; /* etc. */ }


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Hands-on 2 MANAGING PERSISTENT OBJECTS


Based on: Goncalves, 2010: Beginning Java™ EE 6 Platform with GlassFish™ 3

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Hands-on 2

1. Import the «hands-on-2» project.

2. Create the following entities: Address and Customer

Fields of Address: id, street1, city, zipcode und country.

Fields of Customer: id, firstName, lastName, email und address.

Please give the entities a unique table name.

3. Write a main method in a Main class and enter some data into the database.


2014 pre-msc-is-3 persistence layer

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