The Basics Of NHibernate Object Relational Mapper For 'Net

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The Basics Of NHibernateObject Relational Mapper
For .Net

• Oren Eini
• Orene_at_we-can.co.il

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What Is Object Relational Mapping?
3
NHibernate Overview

• NHibernate is a mature ORM with its roots in
  Javas Hibernate.
• Uses XML to map database structure to object
  structure.
• Very flexible and extensible.
• Active Community and Projects around it.
• Developed Supported by JBoss (www.jboss.org)

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The Unit Of Work Pattern

• "Maintains a list of objects affected by a
  business transaction and coordinates the writing
  out of changes and the resolution of concurrency
  problems." Martin Fowler,http//www.shrinkster.
  com/eha
• Manages a set of changes to business objects. All
  objects that were changed during the Unit Of Work
  are saved when the Unit Of Work is concluded.
• NHibernate works out of the box using Unit Of
  Work. An NHibernate Session has 11 match to a
  Unit Of Work.

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Key Concepts

• Entities
• Value Types
• The Session Factory
• The Session
• Mapping (hbm.xml)

• Advanced Topics
• Components
• User Types

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The Session Factory

• Contains all the information needed to talk to a
  database
• Connection String
• Object Mapping
• Database dialect
• Thread Safe
• Highly Concurrent
• Expensive to create
• Exception Safe (doesnt mean that it wont
  throw!)

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The Session

• Main point to interact with the database
• Responsible for objects persistence and loading.
• Not thread safe
• Not exception safe
• Cheap to create

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Common Usages Patterns

• Session Per Request
• NHibernate Http Module
• Session open on Request_Start
• Session disposed on Request_End
• Session Per Conversation
• Single Session (often disconnected)
• Multiply interactions with the user
• All changes are persisted in the end of the
  conversation.

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Getting To Know The Session

• Find()
• Load()
• Get()
• Save()
• Update()

• BeginTransaction()
• Flush()

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Xml Mapping

• lt?xml version'1.0' encoding'utf-16'?gt
• lthibernate-mapping
• xmlnsxsi'http//www.w3.org/2001/XMLSchema-inst
  ance'
• xmlnsxsd'http//www.w3.org/2001/XMLSchema'
  xmlns'urnnhibernate-mapping-2.0'gt
• ltclass name'NHibernate.Demos.ToDoItem,
  NHibernate.Demos'
• table'ToDo'gt
• ltid name'Id'gt
• ltgenerator class'identity' /gt
• lt/idgt
• ltproperty name'DueDate' /gt
• ltproperty name'Title' /gt
• ltproperty name'Description' /gt
• ltproperty name'PrecentageDone' /gt
• lt/classgt
• lt/hibernate-mappinggt

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Configuration

• lt?xml version"1.0" encoding"utf-8" ?gt
• lthibernate-configuration xmlns"urnnhibernate-con
  figuration-2.0" gt
• ltsession-factorygt
• ltproperty name"connection.provider"gt
  NHibernate.Connection.DriverConnectionProviderlt/pr
  opertygt
• ltproperty name"connection.driver_class"gt
  NHibernate.Driver.SqlClientDriverlt/propertygt
• ltproperty name"connection.connection_string"gt
  Data SourcelocalhostInitial
  CatalogTestIntegrated SecurityTruelt/propertygt
• ltproperty name"dialect"gt NHibernate.Dialect.M
  sSql2000Dialectlt/propertygt
• ltmapping assembly"NHibernate.Demos"/gt
• lt/session-factorygt
• lt/hibernate-configurationgt

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Logging

• NHibernate offers a wealth of information that
  can be turned on / off at runtime using log4nets
  capabilities.
• ltfilter type"log4net.Filter.LoggerMatchFilter"gt
• ltloggerToMatch value"NHibernate" /gt
• ltacceptOnMatch value"true" /gt
• lt/filtergt
• ltfilter type"log4net.Filter.DenyAllFilter" /gt

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What it is not meant for

• Bulk data manipulations Use SPs or SqlBulkCopy
  for this.
• Free developers from understanding the database /
  NHibernate.
• Let you forget the profiler.

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Resources

• Forumshttp//shrinkster.com/egu
• Mailing Listshttp//shrinkster.com/egv
• Hibernate In Action (highly recommended)http//sh
  rinkster.com/egw 
• How to ask questionsPost with relevant code and
  mapping, include what you expected to happen and
  what happened. If an exception occurred, include
  the exception message and full stack.

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Questions Comments
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