Hibernate Introduction - 1

Present by Eric Yu

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Content

Understanding object/relational persistence

Introduction

Architecture

The core interfaces

Configuration

Persistent classes

Basic O/R mapping

Collection mapping

Association mapping

Component mapping

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Understanding O/R persistence

What is persistence?

Object-oriented applications

Relational database system

The paradigm mismatch

Object/relational mapping

What is ORM?

Why ORM (solution)?

productivity, maintainability

performance, vendor independence

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Understanding O/R persistence

What do RDBS do well?Work with large amounts of data

searching, sorting

Work with sets of data

joining, aggregating

Share

concurrency, many applications

Integrity

constraint, transaction isolation

What do RDBS do badly?Modeling

no polymorphism; fine-gained modeling is difficult

Biz logic in stored procedure

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Introduction

HibernateOpen Source (LGPL)

Mature and Popular (15,000 downloads/month)

Custom API

Will be referred by EJB 3.0 in its redesign of entity beans

FeaturesPersistence for POJOs (Plain Ordinary/Old Java Object)

Flexible and intuitive mapping

Support for fine-grained object models

Powerful, high performance queries

Two-level Caching Architecture

Toolset for roundtrip development

Support for detached persistent objects

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Architecture

Figure 1 Figure 2

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The core interfaces

SessionFactory A threadsafe (immutable) cache of compiled mappings for a single database. A factory for Session and a client of ConnectionProvider

Session A single-threaded, short-lived object representing a conversation between the application and the persistent store. Wraps a JDBC connection. Factory for Transaction.

Persistent Objects and CollectionsShort-lived, single threaded objects containing persistent state and business function. These might be ordinary JavaBeans/POJOs,

Transient and detached Objects and CollectionsInstances of persistent classes that are not currently associated with a Session.

Transaction A single-threaded, short-lived object used by the application to specify atomic units of work. Abstracts application from underlying JDBC, JTA or CORBA transaction. A Session might span several Transactions in some cases.

ConnectionProvider (Optional) A factory for (and pool of) JDBC connections. Abstracts application from underlying Datasource or DriverManager. Not exposed to application, but can be extended/implemented by the developer.

TransactionFactory (Optional) A factory for Transaction instances. Not exposed to the application, but can be extended/implemented by the developer.

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Configuration

Objective

Used to build an SessionFactory.

Main items

JDBC connection / datasource

Classes mapping files

Diff for managed and non-managed environments

Two styles

Properties configure file

XML configure file (recommended)

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Configuration

SampleProperties file for

Non-managed env

XML file for

Managed env

<hibernate-configuration><session-factory><property name="hibernate.connection.datasource"> synnex/jdbc/CISDB</property><property name=" hibernate.dialect">org.hibernate.dialect.SybaseDialect</property><property name="hibernate.transaction.factory_class">org.hibernate.transaction.JTATransactionFactory</property><mapping resource="Customer.hbm.xml" /><mapping resource="Address.hbm.xml" /></session-factory></hibernate-configuration>

<hibernate-configuration><session-factory><property name="hibernate.connection.datasource"> synnex/jdbc/CISDB</property><property name=" hibernate.dialect">org.hibernate.dialect.SybaseDialect</property><property name="hibernate.transaction.factory_class">org.hibernate.transaction.JTATransactionFactory</property><mapping resource="Customer.hbm.xml" /><mapping resource="Address.hbm.xml" /></session-factory></hibernate-configuration>

hibernate.connection.url = \ jdbc:sybase:Tds:192.168.200.11:4500/CIShibernate.connection.driver_class = \com.sybase.jdbc2.jdbc.SybDriverhibernate.connection.username = \ericyhibernate.connection.password = \synnex2k2hibernate.transaction.factory_class = \org.hibernate.transaction.JDBCTransactionFactory

hibernate.connection.url = \ jdbc:sybase:Tds:192.168.200.11:4500/CIShibernate.connection.driver_class = \com.sybase.jdbc2.jdbc.SybDriverhibernate.connection.username = \ericyhibernate.connection.password = \synnex2k2hibernate.transaction.factory_class = \org.hibernate.transaction.JDBCTransactionFactory

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Configuration

How to get SessionFactory

For properties file (hibernate.properties)

For XML file (hibernate.cfg.xml)

Configuration cfg = new Configuration().addResource(“Customer.hbm.xml").addResource(“Address.hbm.xml");

// If not use the default configure file// cfg.setProperties(<an instance of java.util.Properties>);SessionFactory sessionFactory = cfg.buildSessionFactory();

Configuration cfg = new Configuration().addResource(“Customer.hbm.xml").addResource(“Address.hbm.xml");

// If not use the default configure file// cfg.setProperties(<an instance of java.util.Properties>);SessionFactory sessionFactory = cfg.buildSessionFactory();

SessionFactory sf = new Configuration().configure().buildSessionFactory();

// If not use the default configure file SessionFactory sf = new Configuration().configure(“cisdb.cfg.xml”).buildSessionFactory();

SessionFactory sf = new Configuration().configure().buildSessionFactory();

// If not use the default configure file SessionFactory sf = new Configuration().configure(“cisdb.cfg.xml”).buildSessionFactory();

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Persistent classes

Example

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Persistent classes

Persistent classDeclare accessors and mutators for persistent fields

Implement a no-argument constructor

Provide an identifier property

Prefer non-final classes

Collection property is an interface

Class samplepublic class AuctionItem { private Long _id; private Set _bids; private Bid _successfulBid private String _description;

public AuctionItem () {};

public Long getId() { return _id; } private void setId(Long id) { _id = id; } public String getDescription() { return _description; } public void setDescription(String desc){ _description=desc; }

…}

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Persistent classes

XML MappingReadable metadata

Column/table mappings

Surrogate key generation strategy

Collection metadata

Fetching strategies

XML Sample<hibernate-mapping> <class name=“AuctionItem” table=“AUCTION_ITEM”>

<id name=“id” column=“ITEM_ID”><generator class=“native”/>

</id><property name=“description” column=“DESC”/><many-to-one name=“successfulBid”column=“SUCCESSFUL_BID_ID”

class=“Bid”/><set name=“bids” cascade=“all”

lazy=“true”><key column=“ITEM_ID”/><one-to-many class=“Bid”/>

</set> </class></hibernate-mapping>

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Persistent classes

Code sampleAuctionItem item = new AuctionItem();item.setItemName(“XXX”);…

Session session = null; Transaction tx = null;

try { session = sessionFactory.openSession();

tx = session.beginTransaction(); // do your work session.save(item); tx.commit();}catch (Exception e) { if (tx != null) tx.rollback(); throw e;}finally { if (session != null) session.close();}

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Basic O/R mapping

class<class

name="ClassName" (1)table="tableName" (2)discriminator-value="discriminator_value" (3)mutable="true|false" (4)schema="owner" (5)catalog="catalog“ (6)dynamic-update="true|false" (8)dynamic-insert="true|false" (9)select-before-update="true|false" (10)where="arbitrary sql where condition" (12)batch-size="N" (14)optimistic-lock="none|version|dirty|all" (15)lazy="true|false" (16)

/>

(1) name: The fully qualified Java class name of the persistent class (or interface).

(2) table (optional - defaults to the unqualified class name): The name of its database table.

(15)optimistic-lock (optional, defaults to version): Determines the optimistic locking strategy.

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Basic O/R mapping

id<id

name="propertyName" (1) type="typename" (2) column="column_name" (3) unsaved-value="null|any|none|undefined|id_value" (4) access="field|property|ClassName"> (5)

<generator class="generatorClass"/> (6)</id>

(1) name: The name of the identifier property.(2) type: A name that indicates the Hibernate type.(3) column (optional - defaults to the property name): The name of the primary key column.(4) unsaved-value (optional): An identifier property value that indicates that an

instance is newly instantiated (unsaved), distinguishing it from detached instances that were saved or loaded in a previous session.

(6) The built-in generator: assigned, hilo, seqhilo, increment, identity, sequence, native, uuid (hibernate 3.0), foreign, select (hibernate 3.0)

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Basic O/R mapping

composite-id<composite-id

name="propertyName"class="ClassName"unsaved-value="undefined|any|none"access="field|property|ClassName">

<key-property name="propertyName" type="typename" column="column_name"/><key-many-to-one name="propertyName class="ClassName"

column="column_name"/>......</composite-id>

For Example :(1)<composite-id>

<key-property name=“orderNo“ column=“order_no”/><key-property name=“orderType“ colunm=“order_type”/>

</composite-id>(2)<composite-id>

<key-many-to-one name=“customerNo“ column=“cust_no” class=“Customer”/><key-property name=“locationNo“ colunm=“loc_no”/>

</composite-id>

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Basic O/R mapping

version<version

column="version_column“ (1)name="propertyName" (2)type="typename" (3)access="field|property|ClassName“ (4)unsaved-value="null|negative|undefined" (5)

/>

(1) column (optional - defaults to the property name): The name of the column holding the version number.

(2) name: The name of a property of the persistent class.(3) type (optional - defaults to integer): The type of the version number. Version numbers

may be of Hibernate type long, integer, short, timestamp or calendar.(4) access (optional - defaults to property): The strategy Hibernate should use for accessing the

property value.(5) unsaved-value (optional - defaults to undefined): A version property value that indicates

that an instance is newly instantiated (unsaved), distinguishing it from detached instances that were saved or loaded in a previous session. (undefined specifies that the identifier property value should be used.)

Declaring a nullable version or timestamp property is an easy way to avoid any problems with transitive reattachment in Hibernate, especially useful for people using assigned identifiers or composite keys!

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Basic O/R mapping

property<property name="propertyName" (1)

column="column_name" (2)type="typename" (3)update="true|false" (4)insert="true|false" (4)formula="arbitrary SQL expression" (5)lazy="true|false" (7)unique="true|false" (8)not-null="true|false" (9)optimistic-lock="true|false" (10)

/>(4) update, insert (optional - defaults to true) : specifies that the mapped columns should be

included in SQL UPDATE and/or INSERT statements. (5) formula (optional): an SQL expression that defines the value for a computed property.(7) lazy (optional - defaults to false): Specifies that this property should be fetched lazily when

the instance variable is first accessed.(8) unique (optional): Enable the DDL generation of a unique constraint for the columns. (9) not-null (optional): Enable the DDL generation of a nullability constraint for the columns.(10) optimistic-lock (optional - defaults to true): Specifies that updates to this property do or

do not require acquisition of the optimistic lock. In other words, determines if a version increment should occur when this property is dirty.

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Collection (<set>, <list>, <map>, <bag>, <array>)

Example - set

Collection mapping

element class

public class Product { private String serialNumber; private Set images = new HashSet();}===========================<class name="Product"> <id name="serialNumber" column="productSerialNumber"/>

<set name="images" table="ITEM_IMAGE"> <key column="ITEM_ID"/> <element type="string“ column="FILENAME" /></set>

</class>

public class Product { private String serialNumber; private Set parts = new HashSet();}==========================<class name="Product"> <id name="serialNumber" column="productSerialNumber"/>

<set name="parts"> <key

column="productSerialNumber“/> <one-to-many class="Part"/> </set>

</class>

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Collection mapping

Example - list Example - mappublic class Customer { private String customerNo; private List addresses

= new ArrayList(); … … }

=====================<class name=“Customer">… <list name="addresses"> <key column="cust_no"/> <index column="addr_no"/> <one-to-many

class="Address"/> </list>…</class>

public class Customer { private String customerNo; private Map addresses

= new HashMap(); … … }

=====================<class name=“Customer">… <map name="addresses"> <key column="cust_no"/> <index column="addr_no“ type=“integer”/> <one-to-many

class="Address"/> </map>…</class>

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 Association mapping

many-to-one<many-to-one

name="propertyName" (1)column="column_name" (2)class="ClassName" (3)cascade="cascade_style" (4)fetch="join|select" (5)update="true|false" (6)insert="true|false" (6)property-ref="propertyNameFromAssociatedClass" (7)access="field|property|ClassName" (8)unique="true|false" (9)not-null="true|false" (10)optimistic-lock="true|false" (11)lazy="true|false" (12)

/>(1)name: The name of the property(2)column (optional): The name of the foreign key column. This may also be specified

by nested <column> element(s).(3)class (optional): The name of the associated class.(4)cascade (optional): Specifies which operations should be cascaded from the parent

object to the associated object.(5)fetch (optional - defaults to select): Chooses between outer-join fetching or

sequential select fetching.

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Association mapping

many to one (example)

<class name="Person"> <id name="id" column="personId">

<generator class="native"/> </id> <many-to-one name="address"

column="addressId"not-null="true“class=“Address”/>

</class>

<class name="Address"> <id name="id" column="addressId">

<generator class="native"/> </id></class>

create table Person ( personId bigint not null primary key, addressId bigint not null )create table Address ( addressId bigint not null primary key )

create table Person ( personId bigint not null primary key, addressId bigint not null )create table Address ( addressId bigint not null primary key )

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 Association mapping

one to one (example)A one-to-one association on a foreign key

<class name="Person"> <id name="id" column="personId">

<generator class="native"/> </id> <many-to-one name="address“ column="addressId“

unique="true“ not-null="true"/></class>

<class name="Address"> <id name="id" column="addressId">

<generator class="native"/> </id></class>

create table Person ( personId bigint not null primary key, addressId bigint not null unique)create table Address ( addressId bigint not null primary key )

create table Person ( personId bigint not null primary key, addressId bigint not null unique)create table Address ( addressId bigint not null primary key )

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 Association mapping

one to one (example)A one-to-one association on a primary key

<class name="Person"> <id name="id" column="personId">

<generator class="native"/> </id></class>

<class name="Address"> <id name="id" column="personId">

<generator class="foreign"><param name="property">person</param>

</generator> </id> <one-to-one name="person" constrained="true"/></class>

create table Person ( personId bigint not null primary key )create table Address ( personId bigint not null primary key )

create table Person ( personId bigint not null primary key )create table Address ( personId bigint not null primary key )

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 Association mapping

one to many (example)A one-to-many association on a foreign key

<class name="Person"> <id name="id" column="personId">

<generator class="native"/> </id> <set name="addresses">

<key column="personId“ not-null="true"/> <one-to-many class="Address"/> </set></class>

<class name="Address"> <id name="id" column="addressId">

<generator class="native"/> </id></class>

create table Person ( personId bigint not null primary key )create table Address ( addressId bigint not null primary key, personId bigint not null )

create table Person ( personId bigint not null primary key )create table Address ( addressId bigint not null primary key, personId bigint not null )

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 Association mapping

one to many (example)A one-to-many association on a join table

<class name="Person"> <id name="id" column="personId">

<generator class="native"/> </id> <set name="addresses" table="PersonAddress">

<key column="personId"/><many-to-many column="addressId“ unique="true“ class="Address"/>

</set></class>

<class name="Address"> <id name="id" column="addressId">

<generator class="native"/> </id></class>

create table Person ( personId bigint not null primary key )create table PersonAddress ( personId not null, addressId bigint not null)create table Address ( addressId bigint not null primary key )

create table Person ( personId bigint not null primary key )create table PersonAddress ( personId not null, addressId bigint not null)create table Address ( addressId bigint not null primary key )

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 Association mapping

many to many (example)A many-to-many association on a join table

<class name="Person"> <id name="id" column="personId">

<generator class="native"/> </id> <set name="addresses" table="PersonAddress">

<key column="personId"/><many-to-many column="addressId“ class="Address"/>

</set></class>

<class name="Address"> <id name="id" column="addressId">

<generator class="native"/> </id></class>

create table Person ( personId bigint not null primary key )create table PersonAddress ( personId not null, addressId bigint not null)create table Address ( addressId bigint not null primary key )

create table Person ( personId bigint not null primary key )create table PersonAddress ( personId not null, addressId bigint not null)create table Address ( addressId bigint not null primary key )

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 Component mapping

dependent objects

<class name="Person" table="person"> <id name=“id" column=" personId " type="string">

<generator class="uuid.hex"/> </id> <property name=“name" type=“string"/> <component name=“address" class=“Address">

<property name=“street"/><property name=“zipcode"/><property name=“city"/><property name=“state"/><property name=“country"/>

</component></class>

create table Person ( personId bigint not null primary key,name varchar not null, street varchar null, zipcode varchar null, city varchar null, state varchar null, country varchar null)

create table Person ( personId bigint not null primary key,name varchar not null, street varchar null, zipcode varchar null, city varchar null, state varchar null, country varchar null)

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Inheritance mapping

table per class-hierarchySuppose we have an interface Payment, with implementors CreditCardPayment, CashPayment, ChequePayment. The table per class-hierarchy mapping would look like:

<class name="Payment" table="PAYMENT"> <id name="id" type="long" column="PAYMENT_ID">

<generator class="native"/> </id> <discriminator column="PAYMENT_TYPE" type="string"/> <property name="amount" column="AMOUNT"/>... <subclass name="CreditCardPayment" discriminator-value="CREDIT">

<property name="creditCardType" column="CCTYPE"/> ... </subclass> <subclass name="CashPayment" discriminator-value="CASH"> ... </subclass> <subclass name="ChequePayment" discriminator-value="CHEQUE"> ... </subclass></class>

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Inheritance mapping

table per subclassFour tables are required. The three subclass tables have primary key associations to the superclass table.

<class name="Payment" table="PAYMENT"> <id name="id" type="long" column="PAYMENT_ID">

<generator class="native"/> </id> <property name="amount" column="AMOUNT"/> ... <joined-subclass name="CreditCardPayment" table="CREDIT_PAYMENT">

<key column="PAYMENT_ID"/><property name="creditCardType" column="CCTYPE"/>...

</joined-subclass> <joined-subclass name="CashPayment" table="CASH_PAYMENT">

<key column="PAYMENT_ID"/>...

</joined-subclass> <joined-subclass name="ChequePayment" table="CHEQUE_PAYMENT">

<key column="PAYMENT_ID"/>...

</joined-subclass></class>

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Inheritance mapping

table per subclass, using a discriminator<class name="Payment" table="PAYMENT">

<id name="id" type="long" column="PAYMENT_ID"><generator class="native"/>

</id><discriminator column="PAYMENT_TYPE" type="string"/><property name="amount" column="AMOUNT"/>...<subclass name="CreditCardPayment" discriminator-value="CREDIT">

<join table="CREDIT_PAYMENT"><property name="creditCardType" column="CCTYPE"/>

...</join>

</subclass><subclass name="CashPayment" discriminator-value="CASH">

<join table="CASH_PAYMENT">...

</join></subclass><subclass name="ChequePayment" discriminator-value="CHEQUE">

<join table="CHEQUE_PAYMENT" fetch="select">...</join></subclass>

</class>

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Inheritance mapping

table per concrete classThree tables are involved – no table for the interface (super class).

<class name="Payment"><id name="id" type="long" column="PAYMENT_ID">

<generator class="native"/></id><property name="amount" column="AMOUNT"/>...<union-subclass name="CreditCardPayment" table="CREDIT_PAYMENT">

<property name="creditCardType" column="CCTYPE"/>...

</union-subclass><union-subclass name="CashPayment" table="CASH_PAYMENT">

...</union-subclass><union-subclass name="ChequePayment" table="CHEQUE_PAYMENT">...</union-subclass>

</class>