Intoduction to NHibernate

1. Intoduction to NHibernate

2. Agenda • Overview of NHibernate • Models and Mappings • Configuration • Sessions and Transactions • Queries

3. 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

4. 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 • ver1.0 mirrored the feature set of Hibernate 2.1 • ver1.2.1, 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'sHQL, ... • http://sourceforge.net/projects/nhibernate/files/NHibernate/

5. Mappings • mappinga 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 • settingup a base entity class • handling versioning and concurrency

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

7. 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

8. 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)

9. Persistence and the layered architecture • business layer • is responsible for implementingany business rules or system requirements that users would understand as part of the problem domain • persistence layer • group of classes and componentsresponsible for saving application data to and retrieving it from data store • defines a mapping between the business domain entitiesand the database. • NH lives here !!!

10. Approachesto 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

11. 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

12. 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

13. 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

14. table-per-class • properties of the base class in a shared table • each subclass gets its own table • joined-subclasselement • key element to name the primary key column

15. 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