Hibernate Day2

8/2/2019 Hibernate Day2

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2008, InfosysTechnologies Ltd.

Confidential

Unit 2 : OR Mapping Relations andInheritance

ER/CORP/CRS//003


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Infosys Technologies Ltd.

2008, Infosys Technologies Ltd. Confidential

Hibernate Mapping Files

Object Relational mapping defined in XML document

Mapping documents are readable and hand-editable

Mapping language is java-centric, mapping constructedaround persistent classes not table declaration

Can use tool like XDoclet and annotation

Define identifier generation, properties, objectrelationship ..

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Mapping relationships

Types

one-to-one Either end can be the owner (only one)

many-to-one Many end must be the owner

one-to-many Many end must be the owner

many-to-many Either end can be owner

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One to One Relationship

Expresses a relationship between two classes where

each instance of the first class is mapped to a singleinstance of the second class or vice versa

One to One relationship can be implemented in thedatabase in different two ways

Giving each of the respective tables the same primarykey values

Using foreign key constraint from one table onto aunique identifier column of the other

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Email

PK Id

email

FK- userId

USER

PK Id

userName


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One-To-One Unidirectional

package org.demo;

class Person {

private int personId;

..

private Email address;...

}

package org.demo;

class Email {

private int pk_id;

... }

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The Mapping File

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One-to-Many and Many-to-one AssociationRelationship Representation

By foreign key, with no additional constraints

Link table by maintaining foreign key into each ofassociated tables

Unique constraint to be specified on the one side ofrelation (one to many) else it will be many to many

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USER

PK Id

userName

Email

PK Id

email

USER_Email

PK,FK userId

PK,FK emailId


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One-To-Many Relationship

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One to Many relationship: Creating ObjectInstance Country has many states

public class Country {

private Long countryid;

private String name;

// Country has one-to-many relationship with Statesprivate Set states;

}

public class State {

private Long stateid;private String name;

}

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1.One to Many :Using


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One to Many : Using Set in Domain Class

Country has many states

Country country=new Country();

country.setName(India");

country.setStates(new HashSet());country.getStates().add(new State(Maharashtra));

country. getStates().add(new State(Gujarat));

session.saveOrUpdate(country);

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One to Many relationship :List

public class Author{

private int id;


private List books;

public void setBooks(List l) {bools = l;

}

public List getBooks() {

return books;}

// ...

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2. One to Many relationship:

Author has written many books

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One to Many relationship :

public class Author{

private int id;


private Book[ ] books;

public void setBooks(List l) {bools = l;

}

public List getBooks() {

return books;}

// ...

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One to Many relationship :Object Instance

ArrayList list = new ArrayList();

list.add(new Book(Java"));

list.add(new Book("Servlets"));

list.add(new Book("JSP"));Author sp = new Author(Author1);

sp.setBooks(list);

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Many to Many relationship:

Event has many speakers

public class EventManyToMany {

private Long id;


private int duration;private Set speakers;

public void setSpeakers(Set speakers) {

this.speakers = speakers;

}

public Set getSpeakers() {

return speakers;

}// ...

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Many to Many relationship:

A speaker speaks in many events

public class SpeakerManyToMany {

private Long id;

private String first_Name;

private String last_Name;private Set events;

public Set getEvents() {

return this.events;

}

public void setEvents(Set events) {

this.events = events;

}20


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Many to Many relationship

One Event has many speakers and one speakersparticipates in many events

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2008, InfosysTechnologies Ltd.

Confidential

Mapping Object Inheritance

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Inheritance

Three strategies

One table per class

One table per subclass

One table per concrete class

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Example

class Payment

payment_id

amount

class CreditCardPayment

creditcard_type

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One table per class hierarchy

One table for the whole class hierarchy

A discriminator column is a key to uniquely identify

the base type

Advantages

This hierarchy offers the best performance even for inthe deep hierarchy since single select may suffice

Disadvantages

Changes to members of the hierarchy require column to

be altered, added or removed from the table

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One Table per Class Hierarchy

How to define the mapping

Use element and extend superclass usingextends

define discriminator-value attributes

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One table per Class Hierarchy


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One Table per Subclass

One table for each subclass

Foreign key relationship exists between common

table and subclass tables

Advantages

Using this hierarchy, does not require complexchanges to the database schema when a singleparent class is modified

It works well with shallow hierarchy

Disadvantages As the hierarchy, it may result in poor performance

The number of joins required to construct asubclass class also grows

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Use element and extends attributes

that defines the superclass

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Mapping Inheritance:1 Table for ConcreteClass

Map each of the concrete classes as a normal persistent

class Advantages

It is easiest to implement

Disadvantages

Data that belongs to a parent class is scatteredacross a number of subclass tables, whichrepresents concrete classes

A query couched in terms of parent class is likely tocause a large number of select operations

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Mapping Inheritance:One Table for ConcreteClass Changes to a parent class is reflected to large number of

tables This hierarchy is not recommended for most cases

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One Table per Concrete Class

The mapping of the subclass repeats the properties of

the parent class

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One Table per Concrete Class


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QUERY FACILITY INHIBERNATE

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Query Facility in Hibernate

We can get data from the database using hibernate in 3

different ways 1.Criteria Query

2.HQL

3.Native SQL

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Criteria Query API

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Criteria Query API

Queries can be constructed using a set of Java Objects

instead of query language Lets you assemble nested, structured query expressions

in Java programming language

Compile time syntax checking possible

Polymorphic behavior is supported Eg:get instances of X & subclass(X)

Supports Query By Example (QBE)

Querying by providing an example object whichcontain properties that has to be retrieved

Supports aggregation methods (from Hibernate 3onwards)

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Creating Criteria object

Steps for a Simple Query

1.Create Criteria object(org.hibernate.Criteria) viacreateCriteria() factory method of the Session

2.Pass persistent object's class or the entity name to thecreateCriteria() method

3Call list() method of the Criteria object

Eg:

1.Get all instances of Employee class and its subclasses

Criteria crit = sess.createCriteria(Employee.class);

List results = crit.list();

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Selecting Fewer Rows using :-Restrictions

To the Criteria query object add restrictions with add()

method The add() method takes an Criterion object that

represents an individual restriction

Eg:2// Retrieve Employee data whose name has apattern

Criteria crit = session.createCriteria(Employee.class);

Criterion c= Restrictions.eq(name, Infy)

crit.add(c);


You can have any number of restriction for a Criteriaquery

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Methods of Restriction Class

Restrictions.eq(name, Infy)

Restrictions.ne(name, NoName)

Restrictions.like(name, Sa%)

Restrictions.ilike(name, sa%)

Restrictions.isNull(name);Restrictions.gt(price,new Double(30.0))

Restrictions.between(age, new Integer(2), new

Integer(10))

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Logical Grouping - Restrictions

Eg-3 :Retrieve Employee objects whose name has a

pattern and whose exp is 10 or nullList people = sess.createCriteria(Employee.class)

.add( Restrictions.like("name", R%") )

.add( Restrictions.or(

Restrictions.eq( exp", new Integer(10) ),

Restrictions.isNull(exp)) )

.list();

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Pagination through ResultSet

Hibernate handles the pagination

Retrieving fixed number of objects

Two methods of Criteria class

setFirstResult() To set the first row in the result

setMaxResults() The number of rows to beretrieved

Eg:4 Using pagination


crit.setFirstResult(2);crit.setMaxResults(50);


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Aggregate Functions

avg(String propertyName)

average of a property's value

count(String propertyName)

number of times the given property has a value

countDistinct(String propertyName)

number of unique values the said property contains

max(String propertyName)

min(String propertyName)

sum(String propertyName) sum of the property values

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Aggregate Functions [contd]

We can call different aggregate functions using the

Projections factory class.

Once the projection object is created add it to the criteriaobject using setProjection() method

Eg:-The result will contain one object, an Integer that

Holds the results of executing Avg(Salary)SQL

statement


crit.setProjection( Projections. avg (salary) );List results = crit.list();

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Hibernate Query Language (HQL)

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Hibernate Query Capabilities in 3.0

Newly improved Hibernate Criteria Query API


queries that are provided in the native SQL dialect of thedatabase is also supported

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Very similar to SQL but less verbose

Understands OO concepts like inheritance,polymorphism , association, aggregation, composition

Selection

from, as

Projection

select, elements

Constraints

where Associations and joins-

outer join, full join, inner join, right outer join

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Other constructs-> aggregate functions,

expressions,

group by clauses,

order by clauses,

polymorphic selections,

sub-queries

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Differences from SQL

HQL is fully object-oriented and understands notions

like, polymorphism ,association and inheritance Queries are case-insensitive,but for the names of Java

classes and properties

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Alias

Multiple classes may emerge, resulting in a Cartesian

product or "cross" join.from Employee, Dependants

from Formula as emp, Dependants as deps

Tip:query aliases can be named using an initial lowercase

so that it is consistent with Java naming standards for localvariables

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Join

We may also assign aliases to elements of a collection

of values or to associated entities, using a joinEg1. from Event as evt inner join evt.speakers as spk

left outer join sp.venue as venue

Eg:2 from Event as evt left join evt.speakers.venue as

venue

Eg:3 from Formula form full join form.parameter param

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Join types supported

inner join

left outer join

right outer join

full join (not usually useful)

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select clause

The select clause picks which properties & objects to

return in the query result setselect spk

from Event as evt

inner join evt.speaker as spk

Compact form

select evt.speaker from Event evt

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select clause

properties of any value type including the properties of

component type can be returned by Queriesselect evt.name from Event evt

where evt.name like Hib%'

select cust.name.firstName from Customer as cust

properties as an array of type Object[ ] and/or multiple

objects can be returned by Queries

select mother, offspr, mate.name from DomesticCatas mother inner join mother.mate as mate left outer

join mother.kittens as offspr

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where clause

The list of instances returned can be narrowed by the

Where clause. you may refer to properties by name ,If no alias exists

from Event where name=Hibernate Session'

use a qualified property name ,If there is an alias :

from Event as evt where evt.name= Hibernate Session'

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where clause [cont]

Return all instances of Event for which there exists an

instance of Speaker with a id property equal to the spkidproperty of the Event

select evt

from Event evt, Speaker spk

where evt.spkid = spk.id

Compound path expressions make the where clauseextremely powerful.

from Event evt where evt.speaker.name is not null

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Native SQL Query

Native SQL is SQL in the native format for the database

you are connected to, to performs operations like create,update, delete and select.

Use createSQLQuery() method of session Object topass the query string.

It returns a SQLQuery object Invoke the list() to get the data from the selected

database table

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Native SQL Query [contd]

// Build SQL query

{System.out.println("\n---Using SQL query with where clause...");String sql = "select * from Supplier supplier";SQLQuery query = session.createSQLQuery(sql);query.addEntity("supplier", Supplier.class);List results = query.list();

displaySupplierList(results);

}

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Demo Program


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Demo Program

ID name salary joining_date

1001 John 10000 12-jan-2009

1002 Tommy 20000 13-mar-2008

1003 Angel 23000 14-jun-2008

1004 Joy 22000 23-apr-2007

Table Name:EMPOLOYEE

Entity class Name :Employee

Program to find out the lowest salary amount


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Program to find out the lowest salary amountfrom the table (Aggregate Function)

package demo;

importjava.util.List;import org.hibernate.Query;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.cfg.Configuration;

public class HibernateHQLMinFunction {

public static void main(String[] args) {// TODO Auto-generated method stubSession sess = null;try {SessionFactory sf = new

Configuration().configure().buildSessionFactory();sess = sf.openSession();



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Program to find out the lowest salary amountfrom the table (Aggregate Function) [contd]

String SQL_QUERY = "select min

(salary) from Employee emp";Query query = sess.createQuery(SQL_QUERY);List list = query.list();System.out.println("Min Salary Amount: " + list.get(0));

}catch(Exception e){System.out.println(e.getMessage());

}}



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Program to find out the lowest salary amountfrom the table (Aggregate Function) [contd]

Output:

Min Salary Amount: 10000

Demo 2: Select HQL Example


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Demo 2: Select HQL Example

package demo;;

import org.hibernate.Session;import org.hibernate.*;import org.hibernate.cfg.*;importjava.util.*;

public class SelectHQLExample {public static void main(String[] args) {Session session = null;

try{// prepare hibernate for use after reading the hibernate.cfg.xml

SessionFactory sessionFactory = newConfiguration().configure().buildSessionFactory();

session =sessionFactory.openSession();
http://www.roseindia.net/hibernate/hibernatefromclauseexample.shtmlhttp://www.roseindia.net/hibernate/hibernatefromclauseexample.shtmlhttp://www.roseindia.net/hibernate/hibernatefromclauseexample.shtmlhttp://www.roseindia.net/hibernate/hibernatefromclauseexample.shtml


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Demo 2: Select HQL Example [contd]

//Using from Clause

String SQL_QUERY ="from Employee emp";Query query = session.createQuery(SQL_QUERY);for(Iterator it=query.iterate();it.hasNext();)

{

Employee emp=(Employee)it.next();System.out.println("ID: " + emp.getId());System.out.println("First Name: " + emp.getName());} session.close();

}catch(Exception e){

System.out.println(e.getMessage()); }finally{}}}

Demo 3:Select HQL program->returns an array


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Demo 3:Select HQL program >returns an arrayof Object package demo

import org.hibernate.Session;import org.hibernate.*;import org.hibernate.cfg.*;

importjava.util.*;public class SelectClauseExample {public static void main(String[] args) {Session session = null;

try{

// prepare hibernate for use after reading the hibernate.cfg.xmlSessionFactory sessionFactory = new

Demo 3:Select HQL program->returns an array
http://www.roseindia.net/hibernate/hibernatefromclauseexample.shtmlhttp://www.roseindia.net/hibernate/hibernatefromclauseexample.shtml


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Configuration().configure().buildSessionFactory();session =sessionFactory.openSession();

//Create Select Clause HQLString SQL_QUERY ="Select emp.id,emp.name," + emp.salary,emp.joining

_date from Employee emp";Query query = session.createQuery(SQL_QUERY);

for(Iterator it=query.iterate();it.hasNext();){Object[] row = (Object[]) it.next();System.out.println("ID: " + row[0]);System.out.println("Name: " + row[1]);System.out.println("Amount: " + row[2]);

} session.close();}catch(Exception e){System.out.println(e.getMessage());

}finally{} }}

Demo 3:Select HQL program >returns an arrayof Object [contd]

S


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Summary

Introduction- Introduction to ORM & Hibernate

Hibernate Architecture and FrameworkHibernate Instance States ,Lifecycle Operation

Hibernate Configurations

Primary Key Generation, Composite Key, Hibernate Data

Types

OR Mapping-Relations and Inheritance

Criteria Query API, HQL & native SQL

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Date post:	05-Apr-2018
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Hibernate Day2

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