NHibernate 2. Beginner's Guide. Rapidly retrieve data from your database into.net objects. Aaron B. Cure BIRMINGHAM - MUMBAI

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2 NHibernate 2 Beginner's Guide Rapidly retrieve data from your database into.net objects Aaron B. Cure BIRMINGHAM - MUMBAI

3 NHibernate 2 Beginner's Guide Copyright 2010 Packt Publishing All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews. Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the author, nor Packt Publishing, and its dealers and distributors will be held liable for any damages caused or alleged to be caused directly or indirectly by this book. Packt Publishing has endeavored to provide trademark information about all of the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information. First published: May 2010 Production Reference: Published by Packt Publishing Ltd. 32 Lincoln Road Olton Birmingham, B27 6PA, UK. ISBN Cover Image by Louise Barr (lou@frogboxdesign.co.uk)

4 Table of Contents Preface 1 Chapter 1: First Look 7 What is NHibernate? 8 Why would I use it? 8 Where do I get it? 8 Can I get help using NHibernate? 9 Database table 9 The XML mapping file (hbm.xml) 10 Plain Old CLR Object ( POCO ) 11 Data access 11 Look how easy it is to use! 12 Summary 14 Chapter 2: Database Layout and Design 15 Before you get started 15 Laying the foundation table layouts 16 Time for action creating an ordering system database 16 Table layouts 19 NHibernate assigned IDs 20 Relationships 21 Normal Form 25 Putting it all together 26 Time for action adding some tables to our Ordering system database 26 Summary 35 Chapter 3: A Touch of Class 37 Start up our applications 37 Creating objects 37 Time for action creating our first class 38 Public properties and private variables 45

5 Table of Contents Time for action adding a few properties 46 Converting SQL database types to.net types 50 Properties for Foreign Keys 51 Summary 54 Chapter 4: Data Cartography 55 What is mapping? 55 Types of mapping 56 XML mapping 56 Getting started 57 Classes 57 Properties 58 ID columns 59 Mapping our types 60 Time for action mapping basic types 60 Relationships 72 One-to-many relationships 72 Many-to-many relationships 74 Getting started 76 Time for action mapping relationships 77 Fluent mapping 79 Summary 82 Chapter 5: The Session Procession 83 What is an NHibernate session? 83 Time for action getting ready 84 What is a session factory? 93 Creating your first session 94 Why do we call.commit()? 95 NHibernate session versus database session? 96 Time for action creating a session and doing some CRUD 96 Sessions in ASP.NET 102 Summary 104 Chapter 6: I'm a Logger 105 Why do we need to log? 105 Why log4net? 106 Getting started 107 Configuration 108 Time for action adding some logging 110 NHibernate log messages 113 Appenders 115 [ ii ]

6 Table of Contents Creating a logger 118 Time for action adding some custom logging 120 Summary 123 Chapter 7: Configuration 125 Looking back 125 The basics of configuration 126 Taking a look at the SQL 129 Abstracting the configuration 130 Time for action moving our configuration 132 XML configuration 135 Summary 136 Chapter 8: Writing Queries 137 Using Data Access Objects 137 The basic Data Access Object 138 Time for action creating our basic Data Access Object 139 Data Access Object methods 143 Time for action adding some CRUD methods 146 Coding some GetX() methods 149 The FieldNames structure 150 Time for action expanding our capabilities 152 The ICriteria object 154 Creating a GetAll() method 155 Paging and Sorting GetAll() methods 157 Filtering ICriteria 159 Time for action replacing our inline code 161 Summary 162 Chapter 9: Binding Data 163 Why should we use data binding? 164 Time for action adding an ASP.NET project 164 Basic data binding techniques 170 Common data binding methods 173 A simple templated control 176 Creating a control instance 177 The <asp:listview> control 179 The <asp:objectdatasource> control 180 Time for action adding our first data bound control 182 Direct data binding 188 One last control the <asp:formview> 190 Summary 195 [ iii ]

7 Table of Contents Chapter 10:.NET Security 197 Built-in controls 197 Time for action adding a login to our page 200 Membership providers 201 Location security 202 Configuring our provider 204 Time for action create a membership provider 205 User roles 209 Role providers 210 Provider configuration 210 Summary 212 Chapter 11: It's a Generation Thing 213 Judging requirements 214 CodeSmith 215 nhib-gen 217 AjGenesis 218 Visual NHibernate 221 MyGeneration 221 Time for action using MyGeneration 223 NGen NHibernate Code Generator 227 NHModeller 228 Microsoft T4 templates 232 T4 hbm2net 232 Summary 233 Chapter 12: Odds and Ends 235 Unit of Work and Burrow 235 How does this relate to NHibernate? 237 Blog.Net blogging components 237 maxrequestlength 237 Converting CSS templates 238 Time for action converting a CSS template 239 XML documentation & GhostDoc 246 Summary 248 Appendix: Pop Quiz Answers 249 Chapter 2 Database Layout and Design 249 Relationships 249 Chapter 3 A Touch of Class 249 Mapping 249 Chapter 4 Data Cartography 250 Class mapping 250 [ iv ]

8 Table of Contents Chapter 5 The Session Procession 250 Creating and updating records 250 Chapter 6 I'm Logger 250 Logging 250 Chapter 7 Configuration 251 Basic configuration 251 Chapter 8 Writing Queries 251 Fieldnames and ICriteria 251 Chapter 9 Binding Data 251 Basic data binding 251 Chapter 10.NET Security 252 Access configuration 252 Chapter 12 Odds and Ends 252 Burrowing in 252 Index 253 [ v ]

9 Preface NHibernate is a popular, fast growing Object-Relational Mapper (ORM) with a helpful community of seasoned developers. It is used in thousands of commercial and open source projects. Armed with a set of simple (and mostly free) tools and the knowledge you'll gain from this book, you can quickly and easily create an entire data-bound website, desktop application, windows or web service, or virtually any other.net project you can conceive. What this book covers Chapter 1, First Look, discusses what an object-relational mapper is, what NHibernate is, and the features it provides us. Chapter 2, Database Layout and Design, discusses how your database is constructed, how the data is related, and how to optimize it for the best performance using NHibernate. Chapter 3, A Touch of Class, explains how creating classes to represent your data makes it easy for you to work with the data and allows you to branch from the design of the database, if need be. Chapter 4, Data Cartography, deals with the actual interface to the database with NHibernate, either using XML mapping files, Fluent NHibernate, or no mapping at all. We also talk about lazy loading, using a fieldnames structure to help avoid typos, and generating the database from our mapping files or classes. Chapter 5, The Session Procession, teaches you how to create NHibernate sessions, which use database sessions to retrieve and store data into the database. Chapter 6, I'm a Logger, teaches you how to use the log4net logging framework for creating our own logs and tap into the information provided by NHibernate (including SQL statements) to monitor and troubleshoot our application.

10 Preface Chapter 7, Configuration, explains how to configure our application so, we are ready to retrieve and store data into our database. Additional configuration options are discussed, as well as optional configuration properties for particular situations. Chapter 8, Writing Queries, discusses using NHibernate to actually retrieve data, to include individual records and collections of records. We talk about filtering records and using the fieldnames structure we created earlier to speed up our development. We also talk about adding parameters to make paging and sorting work in data-bound controls. Chapter 9, Binding Data, explains how to use the data methods we created earlier to build a web application that uses our data access layer, the ObjectDataSource, and other data controls to retrieve, display, and even insert/update database data. Chapter 10, NET Security Providers, presents information about controlling access to and restricting the usage of data within a.net web application. We discuss the use of custom membership and role providers with NHibernate to control access to information. Chapter 11, It's a Generation Thing, discusses how to use code generation techniques such as CodeSmith, NHib-Gen, and MyGeneration to automatically generate our data access layer to get us up and running that much quicker. Chapter 12, Odds and Ends, discusses some advanced topics such as the Burrow session management framework and the NHibernate SchemaExport tool. What you need for this book To successfully complete the examples in this book, you will need a copy of either Visual Studio 2008 or You can use any version as long as it includes the web application projects. This could be either a Visual Web Developer Express version or any full version such as Professional. In addition to Visual Studio, you will also need a SQL database server. The examples are generated using SQL Server Express 2008 and SQL Server Management Studio (SSMS) Express. You will also need to download the NHibernate binary files from sourceforge.net. Who this book is for This book is for new and seasoned developers of.net web or desktop applications who want a better way to access database data. It is a basic introduction to NHibernate, with enough information to get a solid foundation in using NHibernate. Some advanced concepts are presented where appropriate to enhance functionality or in situations where they are commonly used. [ 2 ]

11 Preface Conventions In this book, you will find several headings appearing frequently. To give clear instructions on how to complete a procedure or task, we use: Time for action heading 1. Action 1 2. Action 2 3. Action 3 Instructions often need some extra explanation so that they make sense, so they are followed with: What just happened? This heading explains the working of tasks or instructions that you have just completed. You will also find some other learning aids in the book, including: Pop quiz heading These are short multiple choice questions intended to help you test your own understanding. Have a go hero heading These set practical challenges and give you ideas for experimenting with what you have learned. You will also find a number of styles of text that distinguish between different kinds of information. Here are some examples of these styles, and an explanation of their meaning. Code words in text are shown as follows: "This will give us a new DLL project called Ordering.Data inside a folder named Ordering, which contains a solution named Ordering." [ ]

12 Preface A block of code is set as follows: using System; using System.Collections.Generic; using System.Text; namespace Ordering.Data { class OrderHeader { } } When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold: public class OrderHeader { public OrderHeader() { } } Any command-line input or output is written as follows: 07:18: [10] INFO NHibernate.Cfg.Configuration - Mapping resource: Ordering.Data.Mapping.Address.hbm.xml New terms and important words are shown in bold. Words that you see on the screen, in menus or dialog boxes for example, appear in the text like this: Right-click on the Ordering. Console application, and select Add New Item. Warnings or important notes appear in a box like this. Tips and tricks appear like this. [ ]

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15 1 First Look It seems like every single project we begin as developers, no matter how simple, requires some sort of storage. Sometimes this is a simple collection of values in an XML file or a key-value pair in a properties file. However, more often, we need to have access to larger volumes of data, represented in multiple related database tables. In either case, we are generally forced to reinvent the wheel, to create new data retrieval and storage methods for each piece of data we want to access. Enter NHibernate. In this chapter, we will discuss: What NHibernate is and why we should use it HBM mapping files Plain Old CLR Objects (POCOs) Data access classes A simple web page databound to a collection of NHibernate objects

16 First Look What is NHibernate? That's a great question, and I'm glad you asked! NHibernate is an open source persistence layer based on Object-Relational Mapping Techniques or simply a tool that creates a "virtual representation" of database objects within the code. According to the creators of NHibernate: NHibernate is a port of Hibernate Core for Java to the.net Framework. It handles persisting plain.net objects to and from an underlying relational database. Given an XML description of your entities and relationships, NHibernate automatically generates SQL for loading and storing the objects. In simple terms, NHibernate does all the database work, and we reap all the benefits! Instead of writing reams of SQL statements or creating stored procedures that "live" in a different place than our code, we can have all of our data access logic contained within our application. With a few simple "tricks" that we'll discuss in Chapter 4, Data Cartography, not only will our queries be effective, but they will also be validated by the compiler. Therefore, if our underlying table structure changes, the compiler will alert us that we need to change our queries! Why would I use it? Unless you love to write CRUD (Create, Retrieve, Update, Delete) methods over and over for each of the pieces of data you need to access (and I don't know a single developer who does), you are probably looking for a better method. If you're like me, then you know how to lay down an elegant database design (and if you don't, take a peek at Chapter 2, Database Layout and Design). Once the database is ready, you just want to use it! Wouldn't it be nice to create a few tables, and in just a few minutes, have a working set of forms that you can use for all of your basic CRUD operations, as well as a full set of queries to access the most common types of data? We'll discuss some of the ways to automatically generate your NHibernate data files in Chapter 11, It's a Generation Thing. Where do I get it? The home of the NHibernate project is at while the code is housed at SourceForge ( If you download the latest GA (Generally Available, also known as final or stable) bin release (binaries only, no source code) of the NHibernate project, you will have everything you need to get started. As of this writing, the current release is NHibernate GA-bin, and all of the examples have been developed using this version. This version is available at GA/NHibernate GA-bin.zip. [ ]

17 Can I get help using NHibernate? Chapter 1 There is a great community site for NHibernate on the Web called the NHibernate Forge. It is located at and it provides a wealth of resources for the new and veteran NHibernate user. Have a go hero looking at some sample files A basic NHibernate project is composed of three major parts. You will need a mapping file to tell NHibernate how the database is or should be (see the Mapping our types section in Chapter 4) constructed, some data access methods to tell NHibernate what data you want to retrieve or store into the database, and a POCO to allow you to interact with the data. While XML mapping files are commonly used in NHibernate projects, they are not the only way to map data to POCOs (more in Chapter 4). Take a look at some sample files, but don't get too hung up on them. We'll go into more detail in the later chapters. Database table The first item we need to use NHibernate is a database table to map against. In the following screenshot, we define a table named Login with a Primary Key column named Id, two nullable fields to store the FirstName and LastName, and two non-nullable fields to store the UserName and Password. [ ]

18 First Look The XML mapping file (hbm.xml) The following code snippet shows the Login.hbm.xml mapping file for this simple table, with all the information required not only to map the data, but also to create the database from the metadata contained within the mapping file. If we do not want to be able to generate the database from the mapping file, then we can omit all of the sql-type, unique, and index properties. Some immediate information you might pick up from the file are the name of the class that NHibernate will use to map database rows (BasicWebApplication.Common. DataObjects.Login), which is defined in the <class> tag. This says that the BasicWebApplication.Common.DataObjects.Login object is contained in the BasicWebApplication assembly. It further defines that the Login table is the database table we will be mapping to, using the <table> element. There is an <id> tag that defines what the unique identifier (ID) is for the database record, as well as how that identifier is expected to be created. In our case, the <generator class="hilo"> tag specifies that we will be using the hi/lo Persistent Object ID (POID) generator for IDs. The four string fields FirstName, LastName, UserName, and Password are then mapped to the four database columns of the same names, using the <property> tag. <?xml version="1.0" encoding="utf-8"?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="basicwebapplication.common.dataobjects" assembly="basicwebapplication"> <class name="login" table="login"> <id name="id" type="int32" unsaved-value="null"> <column name="id" /> <generator class="hilo" /> </id> <property name="firstname" type="string" /> <property name="lastname" type="string" /> <property name="username" type="string" /> <property name="password" type="string" /> </class> </hibernate-mapping> [ 10 ]

19 Plain Old CLR Object ( POCO ) Chapter 1 The Login.cs class shown in the following code snippet is the POCO, the class that NHibernate will use to map database rows. Each row in the database returned will be instantiated (also known as "newed up") in a new instance of the Login class. The collection of rows will be returned as a generic IList of Login objects or an IList<Login>. Notice how each property in the class Login maps directly to a property element in the hbm.xml file. We really have five public properties on this object, Id, FirstName, LastName, UserName, and Password. Each of these properties was defined earlier in the hbm.xml file and mapped to a database field. When NHibernate retrieves records from the database, it will create a new instance (also known as "new up") of a Login object for each record it retrieves and use the public "setter" (set function) for each property to fill out the object. public partial class Login { public Login() { } } public virtual int Id { get; set; } public virtual string FirstName { get; set; } public virtual string LastName { get; set; } public virtual string UserName { get; set; } public virtual string Password { get; set; } Data access The final class, LoginDataControl.cs, provides CRUD methods for data retrieval, storage, and removal. The session variable is an NHibernate session (you can find out more about session management in Chapter 5, The Session Procession). This class defines a few simple CRUD methods that are used quite often when manipulating database records. The GetById(int id) function allows the user to pass in an integer and retrieve the record with that ID. The GetAll() method returns all of the records in a given table. GetCountOfAll() returns a count of the records in the table, while allowing controls that handle pagination and record navigation to function. public class LoginDataControl { public LoginDataControl() { } ISession session; [ 11 ]

20 First Look } public Login GetById(int id) { Login retval = session.get<login>(id); return retval; } public IList<Login> GetAll() { ICriteria criteria = session.createcriteria<login>(); IList<Login> retval = criteria.list<login>(); return retval; } public int GetCountOfAll() { return GetAll().Count; } Look how easy it is to use! The sample Login.aspx ASP.NET file shows one of the best reasons why we use NHibernate. By using an ObjectDataSource, we can map the NHibernate objects directly to the data-bound controls that will display or interact with them. All we have to do is create an ObjectDataSource to retrieve the data from our data access class (LoginDataControl.cs), create a set of form fields to display the data (like the <asp:gridview> "LoginGrid" below), and let ASP.NET handle all of the tedious work for us. By the way, this page will work exactly as shown there is no page logic in the code behind or anywhere else. All we have in this code is a GridView to present the information and an ObjectDataSource to interact with our DataAccess classes and provide data for the GridView. The GridView has BoundField definitions for all of the fields in our database table as well as Sorting and Paging functions. The ObjectDataSource has methods mapped for Select, Select Count, Insert, and Update. When the GridView needs to perform one of these functions, it relies on the ObjectDataSource to handle these operations. Working in tandem, these two controls (as well as nearly any other data bound control) can provide a very quick and simple interface for your data! <%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="BasicWebApplication.Web._Default" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" " [ 12 ]