NHibernate 3.0 实战手册

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"NHibernate.3.0.Cookbook - 一本关于ORM的好书，由Jason Dentler撰写，包含了70个强大的解决方案，涵盖了NHibernate生态系统的全范围应用。" 《NHibernate 3.0 Cookbook》是针对ORM(Object-Relational Mapping)框架NHibernate的一本实用指南，由Jason Dentler编著。ORM是一种编程技术，它允许开发人员在关系数据库和面向对象程序之间进行映射，从而简化数据访问和管理。这本书特别关注NHibernate 3.0版本，该版本是.NET平台上广泛使用的ORM库。本书的核心在于其70个极具威力的实战食谱，这些食谱旨在帮助开发者充分利用NHibernate的各种功能和解决方案。每个食谱都针对特定问题，提供了详尽的步骤和示例代码，以便读者能够快速理解和应用到实际项目中。食谱内容可能包括但不限于以下主题： 1. **NHibernate安装与配置**：如何在项目中引入NHibernate，设置数据库连接，以及配置映射文件。 2. **对象关系映射**：学习如何定义实体类，映射属性到数据库字段，处理关联关系（一对一、一对多、多对多）。 3. **会话管理**：掌握会话的创建、打开、关闭，以及事务处理策略。 4. **查询语言**：使用HQL（NHibernate查询语言）和 Criteria API 进行复杂查询，包括分页、排序和过滤。 5. **性能优化**：了解缓存策略，延迟加载，批处理和减少数据库交互次数以提高性能。 6. **事件监听和拦截器**：利用NHibernate的事件系统来实现自定义逻辑，如日志记录、数据验证等。 7. **实体生命周期管理**：理解持久化对象的创建、更新、删除操作，以及状态转换。 8. **复杂映射**：处理继承结构，多态性，集合映射，以及自定义类型。 9. **单元测试与集成测试**：使用NHibernate在测试环境中进行数据操作，确保代码质量。 10. **错误调试和最佳实践**：如何识别并解决常见的NHibernate问题，以及遵循的最佳编码和设计原则。通过《NHibernate 3.0 Cookbook》，开发者不仅可以深入理解NHibernate的工作原理，还能获得解决实际问题的宝贵经验。无论你是初学者还是经验丰富的开发者，这本书都将是你在使用NHibernate时不可或缺的参考资料。

Models and Mappings

In this chapter, we will cover the following topics:

f Mapping a class with XML

f Creating class hierarchy mappings

f Mapping a one-to-many relationship

f Setting up a base entity class

f Bidirectional one-to-many class relationships

f Handling versioning and concurrency

f Creating mappings uently

f Mapping with ConfORM

Introduction

NHibernate is a popular, mature, open source object / relational mapper (ORM) based on

Java's Hibernate project. ORMs, such as LINQ to SQL, Entity Framework, and NHibernate,

translate between the database's relational model of tables, columns, and keys to the

application's object model of classes and properties.

The NHibernate homepage,

http://NHForge.org, contains blog posts, a wiki, the

complete reference documentation, and a bug tracker. Support is available through the

very active nhusers Google group at http://groups.google.com/group/nhusers.

The NHibernate source code is hosted on SourceForge at http://sourceforge.net/

projects/nhibernate/

. Precompiled binaries of NHibernate releases are also available

on SourceForge.

Models and Mappings

7. In the editor, enter the following XML in Product.hbm.xml. Let the IntelliSense

guide you.

<?xml version="1.0" encoding="utf-8" ?>

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"

assembly="Eg.Core"

namespace="Eg.Core">

</id>

<property name="UnitPrice" not-null="true"

type="Currency" />

</class>

</hibernate-mapping>

How it works...

In this recipe, we begin by creating our model. The model is the collection of classes that will

be persisted or stored in the database. A persistent class is any class that will be persisted.

An entity class is a persistent class with an ID. An instance of an entity class is called an

entity. So far, our model only contains the Product entity class. We will expand on this model

over the next few recipes.

Notice that our Product class looks just like any other Plain Old CLR Object (POCO) class.

One of the strongly held design decisions in NHibernate is that all entity classes should be

persistence ignorant, that is, they should not know about, or be dependent on NHibernate.

Let's examine the Id property a little closer. The Id property of each Product instance will

contain the primary key value from the database. In NHibernate, this is named the persistent

object identier (POID). Just as the primary key value uniquely identies a row in a database

table, the POID will uniquely identify an entity in memory.

If you are new to NHibernate, this protected setter may look strange to you.

public virtual Guid Id { get; protected set; }

This is a shorthand way to limit access to the Id property. Code outside of the Product class

is unable to change the value of the Id property. However, NHibernate sets properties using

highly optimized reection, ignoring the protected restriction. This keeps your application

from inadvertently altering this value.

Chapter 1

Next, we create our mapping for the Product entity class. Visual Studio uses the

nhibernate-mapping.xsd schema to provide IntelliSense while completing this mapping.

As a general rule, all NHibernate mapping les end with a.hbm.xml extension, and have a

build action of Embedded Resource. NHibernate searches through the embedded resources

in your assembly, loading each one with this extension.

One of the most common mistakes in mapping is forgetting to set the build

action to Embedded Resource. This leads to the "No Persister for class"

MappingException.

Let's break down this XML mapping. Every XML mapping document contains a single

hibernate-mapping element. The xmlns attribute sets the XML namespace. Along

with the schema in our Schema folder, Visual Studio uses this to enable IntelliSense

inside NHibernate mappings.

The

assembly attribute tells NHibernate which assembly, by default, contains our types.

Similarly, the namespace attribute sets the default .NET namespace types in this mapping le.

Together, they allow us to use the simple name Product instead of the full assembly qualied

name of Eg.Core.Product, Eg.Core. Inside the hibernate-mapping element, we have

a class element. The name attribute tells NHibernate that this class element denes the

mapping for our entity class Product.

The

Id element denes the POID. The name attribute refers to the Id property of our

Product class. It is case-sensitive, just as in the C# language.

The

generator element denes how NHibernate will generate POIDs. In this case, we've told

NHibernate to use the guid.comb algorithm. Several other options exist.

The

property elements dene properties on our Product class. Each name attribute

matches the name of a property on our Product class. By default, NHibernate allows null

values. Adding not-null="true" tells NHibernate to disallow null values.

Avoid redundant mappings

In general, it's best to keep your mappings as short and concise as possible.

NHibernate intelligently scans your model and combines this knowledge

with the information provided in the mapping. In most cases, specifying

the types of properties in your mappings only creates redundancies that

must be maintained. The default table name matches the class name,

and each column name matches the corresponding property by default.

It's not necessary to specify this information again. Similarly, you should

avoid setting an attribute in your mapping when it matches an NHibernate

default. For example, adding not-null="false" to each of your

properties is redundant, and makes your mapping difcult to read.

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