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

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. 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

10. 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

11. Post-insert POID generators • require data to be persisted to the database for an ID to be generated - strongly discouraged • identity • select (uses natural id) • sequence-identity • trigger-identity • native

12. 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

13. 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

14. 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

15. one-to-many relationship • relate one entity to another

16. Lazy loading collections • data isn'tloaded from the database until it is required by the application • fetch Movie (Id, Name, Description, UnitPrice, and Director, but no Actors) • creates an instance of the Movie object • sets the properties of the Movie object with the data from the db • creates a special lazy loading object that implements IList<ActorRole>, and sets the Actors property • returns Movie

17. foreach (var actor in movie.Actors) Console.WriteLine(actor.Actor); • lazy loading object is initialized • loads the associated ActorRoledata • disable lazy loading by adding the attribute lazy="false" to the list element

18. Lazy loading proxies • supports lazy loading through the use of proxy objects public class ActorRole : Entity { public virtual string Actor { get; set; } public virtual string Role { get; set; } public virtual Movie Movie { get; set; } } • proxy object is a subclass of Movie – requirements • Movie cannot be a sealedclass • Movie must have a protected or public constructor without parameters • All public members of Movie must be virtual. This includes methods

19. choices for the creation of these proxy objects • traditional choice DynamicProxy, part of the Castle • LinFu • Spring.NET • build your own • lazy="false" on the class element of our Movie mapping to disable

20. Collections • most common types • allcollections may also use the ICollectiontype • custom NHibernate.UserType.IuserCollection

21. Setting up a base entity class • NH relies on the Equals() to determine equality • application should not be aware of proxy objects • Product instance with an ID of 8 should be equal to a different Product instance or Product proxy with an ID of 8 • transient object is an object that has not been persisted to the db

22. Versioning and concurrency • optimistic and pessimistic concurrency • version element UPDATE Product SET Version = 2 /* @p0 */, Name = 'Junk' /* @p1 */, Description = 'Cool' /* @p2 */, UnitPrice= 100 /* @p3 */ WHERE Id = '764de11e-1fd0-491e-8158-9db8015f9be5' /* @p4 */ AND Version = 1 /* @p5 */ • If no rows updatedStaleStateException • the entity in memory is stale, or out of sync with the db

23. DateTime-based version fields • Datetime, DateTime2, timestamp • attribute optimistic-lock • <class name="Product"dynamic-update="true„optimistic-lock="dirty">

24. Other mappings options • Fluent Nhibernate public ProductMapping() { Id(p => p.Id) .GeneratedBy.GuidComb(); DiscriminateSubClassesOnColumn("ProductType"); Version(p => p.Version); NaturalId() .Not.ReadOnly() .Property(p => p.Name); Map(p => p.Description); Map(p => p.UnitPrice) .Not.Nullable(); }

25. ConfORM • convention-based mappings • mapper outputs anHbmMappingobject built from our conventions • ConfORM uses conventions and patterns to build a mapping directly from the model • Customizable

26. Bidirectional one-to-many class relationships • ORMsare designed to overcome the impedance mismatchbetween the object model and the relational model • inverse attribute - determine which end of the relationship controls the foreign key • we must keep both sides of relationship in sync

27. Mappings enumerations • improperly mapped enumeration can lead to unnecessary updates • by default, NH will map an enumeration to an int • AcctType= AccountTypes.Corporate • AcctTypedatabase field = 2 • int doesn't describe the businessmeaning • store the name of the enumeration value • AcctTypedatabase field „Corporate“ • typeattribute • we tell NHibernate to use a custom class for conversion between .NET types and the database

28. Configuring NHibernate with App.config • proxyfactory.factory_class • specifies the proxy framework we'll use • dialect • specifies a dialect class that NHibernate uses to build SQL syntax • connection.connection_string_name • references our connection string • adonet.batch_size • group SQL DMLstatements in a single ADO.NET command • mapping- where NHwillsearch for our mappings

29. components of NH app • session represents a unit of work • NH session tracks changes to entities and writes those changes back to the database all at once • transactional write-behind

30. Dialects and drivers • Microsoft SQL Server • CE, 7, 2000, 2005, 2008 • Oracle • Lite, 8i, 9i, 10g • MySql • MySql, MySql5 • PostgreSQL, DB2, Informix, Sybase, Firebird, SQLite, Ingres

31. Configuring NHibernate with hibernate.cfg.xml • separate xml configuration file