Hibernate: the short version

Björn Granvik, Jayway

Overview

• Dry run: Theory• Wet run: Lab

– Tutorial part 1: Store two tables with straight Hibernate and do the same using Spring.

– Tutorial part 2: More relationships

Write the SQL

CREATE TABLE users (

LogonID varchar(20) NOT NULL default 0,

Name varchar(40) default NULL,

Password varchar(20) default NULL,

EmailAddress varchar(40) default NULL, LastLogon datetime default NULL,

PRIMARY KEY (LogonID)

);

Create the Pojo

public class User {private String userID;private String userName;private String password;...public String getID() {

return userID;}public void setID(String newUserID) {

userID = newUserID;}...

}

Write the hbm file

<hibernate-mapping>

<class name=”dbdemo.User" table="users">

<id name="ID" column="LogonId" type="string">

<generator class=”native"/>

</id>

<property name="userName"

column="Name” type="string"/>

<property name="password" type="string"/>

<property name="emailAddress" type="string"/>

<property name="lastLogon" type=”java.util.Date"/>

</class>

</hibernate-mapping>

Property file

hibernate.connection.driver_class=org.gjt.mm.mysql.Driver

hibernate.connection.url=jdbc:mysql://localhost/testdb

hibernate.connection.username = gsmith

hibernate.connection.password = sesame

...

caches etc

So far

• User.java - Java bean object to persist • User.hbm.xml - Hibernate mapping file • hibernate.properties - properties file with JDBC

connection info• SQL User table in your database

What to do

• Create a Pojo• Tell the DB about the type of objects you want to

store • Create a Session to your database of choice • Load, Save and Query your objects • flush() your Session back to the database

Example: Setup

// Set up configuration

... conf

// Then build a session to the database

SessionFactory sf = conf.buildSessionFactory();

session = sf.openSession();

Example: Save

// Create new User and store it in db

User newUser = new User();

newUser.setID("joe_cool");

newUser.setUserName("Joseph Cool");

...

// And call Hibernate to store it

session.save(newUser);

Example: Get single user

User newUser = (User)session.load(User.class, suserId);

Example: Get users

List myUsers = session.find("from User");

for (Iterator i = myUsers.iterator(); i.hasNext();) {

User nextUser = (User) i.next();

System.out.println("Resetting password for User: "

+ nextUser.getUserName());

nextUser.setPassword("secret");

}

...

Example: flush

// close our session and release resources

session.flush();

session.close();

OR vs. Relational model

• Java object identity, equality, primary keysa == b

a.equals(b)

• Polymorphism• Joining tables vs. navigating associations

– (bi)birectional relations

• Detach

Detached objects

Retrieve an AuctionItem and change the description:

Session session = sessionFactory.openSession();Transaction tx = session.beginTransaction();AuctionItem item =

(AuctionItem) session.get(ActionItem.class, itemId);tx.commit();session.close();

Bid bid = new Bid();bid.setAmount(bidAmount);bid.setItem(item);item.getBids().add(bid);

Session session2 = sessionFactory.openSession();Transaction tx = session2.beginTransaction();session2.update(item);tx.commit();session2.close();

One-to-One

Java usage:

Bar myBar = Foo.getBar();

Mapping file: Mapping file:

<class name=“Foo”>

...

<one-to-one name=“bar” class=“Bar” />

</class>

Schema:

Foo Bar

id id

One-to-Many

Java usage:

Set myBars = Foo.getBars();

Mapping file: Mapping file:

<class name=“Foo”> ”>

...

<set role=“bars” table=“bar” inverse=“true”>

<key column=”foo_id” />

<one-to-many class=“Bar”>

</set>

</class>

Schema:

Foo Bar

id id, foo_id

One-to-Many

Java usage:Set myBars = Foo.getBars();

Mapping file: Mapping file:<class name=“Foo”> ”>...

<set role=“bars” table=“bar” inverse=“true” lazy=“true” cascade=”orphan-delete”>

<key column=”foo_id” /><one-to-many class=“Bar”>

</set></class>

Schema:Foo Barid id, foo_id

Many-to-Many

Java usage:

Set myBars = Foo.getBars();

Mapping file: Mapping file:

<class name=“Foo”> ”>

...

<set role=“bars” table=“Foo_Bar”>

<key column=”foo_id” />

<many-to-many column=“bar_id” class=“Bar”>

</set>

</class>

Schema:

Foo Bar Foo_Bar

id id foo_id, bar_id

No relationalclass FooBar!

Much more

• Criteria• Query by example• Composites

• Version 3.0

CriteriaList cats = sess.createCriteria(Cat.class)

.add( Expression.like("name", "Fritz%") )

.add( Expression.between("weight",

minWeight, maxWeight) )

.list();

Query by exampleExample example = Example.create(cat

.excludeZeroes() //exclude zero valued properties

.excludeProperty("color") //exclude the property "color"

.ignoreCase(

.enableLike(); //use like for string comparisons

List results = session.createCriteria(Cat.class)

.add(example)

.list();