Hibernate Configuration

1
Hibernate Configuration

• Shahid Amlani
• Abdul Basit
• Hamdan Ahmed
• Sukhmeet Toor

2
Overview

• Hibernate Configuration File
• Persistent Classes
• O/R Mapping
• Associations

3
Configuration

• 2 ways to perform configuration
• hibernate.cfg.xml
• new Configuration().configure()
• Direct Instantiation
• By specifying .addClass(), .addProperty()
• Ultimately interested in session
• sessionFactory configuration().sessionFactory()
• sessionFactory.getCurrentSession()

4
Auto Mapping

• An alternative (sometimes better) way is to
  specify the mapped class, and let Hibernate find
  the mapping document for you
• Configuration cfg new Configuration()
  .addClass(org.hibernate.auction.Item.class)
  .addClass(org.hibernate.auction.Bid.class)

5
Persistent Classes

• Look like Java Beans.
• 2 requirements
• No argument constructor so that
  Constructor.newInstance() can be called
• Unique identifier property
• Each class has a corresponding hibernate xml file

6
O/R Mapping

• For objects, ends with .hbm.xml for every
  persistent class
• These can get very complex. Well just look at
  the top level

7
Associations

• 4 types
• Many-to-One
• An ordinary association to another persistent
  class is declared using a many-to-one element.
  The relational model is a many-to-one
  association a foreign key in one table is
  referencing the primary key column(s) of the
  target table.
• One-to-One
• A one-to-one association to another persistent
  class is declared using a one-to-one element.

8
Collection Mappings

• The Hibernate mapping element used for mapping a
  collection depends upon the type of the
  interface. For example, a element is used
  for mapping properties of type Set.
• Apart from , there is also , ,
  , and mapping
  elements.

9
Associationscont

• Many-to-Many
• Any collection of values or many-to-many
  association requires a dedicated collection table
  with a foreign key column or columns, collection
  element column or columns and possibly an index
  column or columns.
• One-to-Many
• A one to many association links the tables of two
  classes via a foreign key, with no intervening
  collection table.

10
Hibernate Query Language (HQL)

• Hibernate is equipped with an extremely powerful
  query language that (quite intentionally) looks
  very much like SQL.
• Mainly differs from SQL by being object-oriented
  rather than Tuple based.

11
The basics

• The simplest query
• from eg.Cat
• from Cat
• from Cat as cat
• from Cat cat
• All are equivalent and return all persistent
  instances of class Cat

12
Joins

• HQL supports all types of joins from SQL
• Examples
• from Formula, Parameter
• from Cat as cat inner join cat.mate as mate
  left outer join cat.kittens as kitten
• from Cat as cat left join cat.mate.kittens as
  kittens

13
The Select clause

• The select clause picks which objects and
  properties to return in the query result set.
• Examples
• select matefrom Cat as cat inner join cat.mate
  as mate
• select cust.name.firstName from Customer as cust

14
More on Select

• Queries may return multiple objects and/or
  properties as an array of type Object
• select mother, offspr, mate.name from
  DomesticCat as mother inner join mother.mate as
  mate left outer join mother.kittens as offspr
• or as a List,
• select new list(mother, offspr, mate.name) from
  DomesticCat as mother inner join mother.mate as
  mate left outer join mother.kittens as offspr

15
More on Select

• Or as an actual typesafe Java object,
• select new Family(mother,mate,offspr) from
  DomesticCat as mother join mother.mate as mate
  left join mother.kittens as offspr(assuming
  that the class Family has an appropriate
  constructor)
• Provides a lot of flexibility in a single query

16
Where is Where?

• The where clause allows you to narrow the list of
  instances returned
• from Cat where name'Fritz'
• from Cat as cat where cat.name'Fritz'
• select foo from Foo foo, Bar bar where
  foo.startDate bar.date

17
Caveats

• HQL is extremely powerful, but has limitations
• Report generation
• Simple HQL translates to really complicated SQL
  (can be a real MESS)

18
References

• An excellent tutorial on Hibernate
• http//www.hibernate.org/hib_docs/v3/reference/en/
  html/tutorial.html
• Questions?