Intoduction to NHibernate

Agenda

• Overview of NHibernate• Models and Mappings• Configuration• Sessions and Transactions• Queries

What is Nhibernate ?

• mature, ORM solution for .NET platform• free, GNU Lesser General Public License• mapping an object-oriented domain model to a relational

database• home == nhforge.org• files on sourceforge• groups http://groups.google.com/group/nhusers• Commercial support

– hibernating rhinos - Ayende Rahien– imeta - Steve Strong, Fabio Maulo

History• started as port of the popular Java O/R mapper

Hibernate to .NET• Hibernate was started in 2001 by Gavin King• NHibernate was started around 2003

– ver 1.0 mirrored the feature set of Hibernate 2.1– ver 1.2.1, released in 11/2007, features from Hibernate 3 and

support for .NET 2.0, stored procedures, generics, and nullable types

– ver 2.0 was released 08/2008. Comparable to Hibernate 3.2. .NET 1.1

– ver 3.0 - December 04, 2010 - .NET 3.5. • LINQ support, strongly typed criteria-like API called QueryOver, new AST-

based parser for NHibernate's HQL, ...

– http://sourceforge.net/projects/nhibernate/files/NHibernate/

Mappings

• mapping a class with XML– Keys, ID generators

• table-per-class hierarchy• table per class• table per concrete class• one-to-many relationship

– lazy loading collections, lazy loading proxies

• setting up a base entity class• handling versioning and concurrency

• bidirectional one-to-many class relationships• mappings enumerations• creating class components

mapping a class with XML

• 2x .xsd – intellisense• mapping file - XML - extension .hbm.xml• set Build Action to Embedded Resource !!!• model - collection of classes that will be

persisted in the database• persistent class - any class that will be

persisted (e.g. Person, Address)• entity class - a persistent class with an ID

• entity - an instance of an entity class• POCO - Plain Old CLR Object

– POCOs are objects not burdened with inheritance or attributes needed for specific frameworks

• all entity classes should be persistence ignorant

– strongly held design decisions in NHibernate

• Id property - primary key value from the db• persistent object identifier (POID)

Persistence and the layered architecture

• business layer – is responsible for implementing any business rules or

system requirements that users would understand as part of the problem domain

• persistence layer – group of classes and components responsible for

saving application data to and retrieving it from data store

– defines a mapping between the business domain

entities and the database. – NH lives here !!!

Approaches to begin developing an NH application

• model-first– create model -> map the model -> generate our

database tables from the model and mappings

• configuration-first • database-first

Non-insert POID generators

• assign an identity to a persistent object without writing the object's data to the db

• hilo• guid• guid.comb• guid.native• uuid.hex, uuid.string• counter, increment• sequence, seqhilo

Post-insert POID generators

• require data to be persisted to the database for an ID to be generated

• identity• select (uses natural id)• sequence-identity• trigger-identity• native

table-per-class hierarchy

• data for our entire hierarchy is stored in a single table

• discriminator column ProductType– distinguish among products, books, and movies– by default, the contains the class name– Eg.Core.Product, Eg.Core.Book, or Eg.Core.Movie

• subclass properties as must be nullable• suggested method for mapping class hierarchies

table-per-class

• properties of the base class in a shared table• each subclass gets its own table• joined-subclass element

– key element to name the primary key column

table-per-concrete class

• each class gets its own table • containing columns for all properties of the class

and the base class• there is no duplication of data• union-subclass element