NHibernate for .NET

NHibernate for .NET
Albert Kuo
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Introduction to ORM
Introduction to NHibernate
Scenario
NHibernate Demo
Demo Process
Hibernate-config.xml
Mapping files & classes
SessionManager
DAO (Data Access Object)
Create ASPX to do testing
Reference
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Agenda

Introduction to ORM
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Object-relational mapping (aka ORM, O/RM, and O/R mapping) is a programming technique for converting data between incompatible type systems in relational databases and object-oriented programming languages (Wikipedia)
Objects are hierarchical
Databases are relational
What is ORM?
ORM
objects
relational
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Productivity
Eliminates lots of repetitive code – focus on business logic
Database schema is generated automatically
Maintainability
Fewer lines of code – easier to understand
Easier to manage change in the object model
Performance
Lazy loading – associations are fetched when needed
Caching
Database vendor independence
The underlying database is abstracted away
Can be configured outside the application
ORM Benefits
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ORM and Architacture
Oracle, MS SQL Server, DB2, MySQL, Sybase, etc.

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Initially developed for Java
created in late 2001 by Gavin King
absorbed by the JBossGroup / Red Hat
Ported to .NET 1.1, 2.0, 3.5
Resulting product called “NHibernate”
All popular databases supported
Oracle, SQL Server, DB2, SQLite, PostgreSQL, MySQL, Sybase, Firebird, …
XML-based configuration files
Good community support
Free/open source -NHibernateis licensed under the LGPL (Lesser GNU Public License)
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High-level overview of the Nhibernate API

NHibernate managing database access
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Access Persistent Object

ISessionFactory
One per database (or application)
Expensive to create
Reads configuration
ISession
Portal to the database
Saves, retrieves
ITransaction
Encapsulates database transactions
Nhibernate in a Nutshell
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Scenario
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One people may have more than one contact
One contact belongs to one people
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Database schema

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Use Case Diagram

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Sequence diagram – create

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Sequence diagram – Read

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Sequence diagram – Update

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Sequence diagram – Delete

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Project Directories
Stored persistence tier-related code
Stored presentation tier-related code
Data access objects
Value objects and mapping files

NHibernate
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Libraries
Required library
Required for lazy loading
Antlr3.Runtime.dll
Iesi.Collections.dll
log4net.dll
NHibernate.dll
Castle.Core.dll
Castle.DynamicProxy2.dll
NHibernate.ByteCode.Castle.dll
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Demo Process

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<class> declare a persistent class
<id> defines the mapping from that property to the primary key column
Specifies strategy
<property> declares a persistent property of the class
<component> maps properties of a child object to columns of the table of a parent class.
Associations
One-to-Many
Many-to-One
Many-to-Many
One-to-One (uncommon)
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Mapping Concepts

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Mapping Collections

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Mapping files & classes
ORM
objects
relational

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Mapping files & classes – cont.

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Session Manager
[ISession]

Obtained from a SessionFactory instance
Responsible for storing and retrieving objects
Think of it as a collection of loaded objects related to a single unit of work

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DAO (Data Access Object)

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DAO (Data Access Object) – cont.

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Transaction: A set of database operations which must be executed in entirety or not at all
Should end either with a commit or a rollback
All communication with a database has to occur inside a transaction!
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Transactions

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Transactions – cont.

Create a new record

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Read data by criteria

Update record

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Delete record

O/R Mapping
http://en.wikipedia.org/wiki/Object-relational_mapping
Official site
www.hibernate.org
NHibernate in Action
NHibernate Made Simple
http://www.codeproject.com/KB/database/Nhibernate_Made_Simple.aspx
NHibernate Best Practices
http://www.codeproject.com/KB/architecture/NHibernateBestPractices.aspx
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Reference