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Learning NHibernate 4

Learning NHibernate 4

By : Suhas H Chatekar
3.6 (9)
Buy this Book
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Learning NHibernate 4

Learning NHibernate 4

3.6 (9)
By: Suhas H Chatekar
Buy this Book

Overview of this book

This book targets .NET developers who have never used an ORM before, developers who have used an ORM before but are new to NHibernate, or have used NHibernate sparingly and want to learn more about NHibernate.
Table of Contents (13 chapters)
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Preface
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Preface
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What this book covers
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What you need for this book
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Who this book is for
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Conventions
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Reader feedback
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Customer support
Lock Free Chapter
1
1. Introduction to NHibernate
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1. Introduction to NHibernate
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What is ORM?
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What is NHibernate?
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What is new in NHibernate 4.0?
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NHibernate for users of Entity Framework
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Is using ORM a bad idea?
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Building blocks of NHibernate
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Summary
2
2. Let's Build a Simple Application
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2. Let's Build a Simple Application
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Explaining the approach used in learning NHibernate
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The problem statement
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The development setup
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The domain model
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Adding some code
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Summary
3
3. Let's Tell NHibernate About Our Database
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3. Let's Tell NHibernate About Our Database
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Important NHibernate terminology
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Mapping the prerequisites
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Different mechanisms to write the mappings
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XML mappings for the Employee class
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Identifier generation
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Mapping associations
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Mapping inheritance
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Mapping components
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Mapping by code
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Fluent mapping a.k.a. Fluent NHibernate
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Choosing the right mapping method
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Summary
4
4. NHibernate Warm-up
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4. NHibernate Warm-up
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Warming up NHibernate succinctly
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The NHibernate session architecture
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XML configuration
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Programmatic configuration
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Loquacious configuration
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Fluent configuration
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Configuration options
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Generating the database scripts from mappings
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Summary
5
5. Let's Store Some Data into the Database
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5. Let's Store Some Data into the Database
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Entity states
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Transactions and unit of work
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Saving entities
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Transitive persistence using cascade styles
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Transitive persistence/cascading in action
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Bidirectional associations and ownership
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Order of operations
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Entity equality
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The architecture diagram
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Summary
6
6. Let's Retrieve Some Data from the Database
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6. Let's Retrieve Some Data from the Database
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Querying the workflow
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Different querying methods
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Joins
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Lazy loading
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Eager fetching
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Pagination and ordering of results
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Retrieving entities by identifiers
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Polymorphic queries
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Summary
7
7. Optimizing the Data Access Layer
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7. Optimizing the Data Access Layer
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Baseline and optimize
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Organization of the chapter
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Batching
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Fetching strategies
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Avoiding the select N+1 problem
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Avoiding eager fetching
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Using extra-lazy for lazy collections
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Summary
8
8. Using NHibernate in a Real-world Application
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8. Using NHibernate in a Real-world Application
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What kind of application are we building?
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Architectural principles we will follow
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Feature 1 – onboarding an employee
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Unit of work
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Feature 2 – updating the details of an employee
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Feature 3 – searching employees
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Summary
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9. Advanced Data Access Patterns
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9. Advanced Data Access Patterns
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Problems with the repository pattern
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Specification pattern
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Query object pattern
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Summary
10
10. Working with Legacy Database
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10. Working with Legacy Database
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Composite IDs
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Components
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Join-mapping to load data from multiple tables
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Working with database views
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Using subselect instead of views
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Working with stored procedures
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Using custom DTOs
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Summary
11
11. A Whirlwind Tour of Other NHibernate Features
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11. A Whirlwind Tour of Other NHibernate Features
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Concurrency control
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Event system
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Caching
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Stateless sessions
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User-defined types
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Summary
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Index
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Index

Avoiding the select N+1 problem

We had briefly mentioned select N+1 problem in the previous chapter. Select N+1 is bad from both performance and memory consumption point of view. We are going to discuss how we can avoid this problem. Before we get our hands dirty, let's spend some time trying to understand what is select N+1 problem.

What is the select N+1 problem?

It is easier to understand select N+1 problem if we read it in reverse – 1+N select. That is right. Let's see how.

Suppose you want to load all employees living in London and then for every employee iterate through the benefits that they are getting. Following is one way of doing that using a LINQ query:

[Test]
public void WithSelectNPlusOneIssue()
{
  using (var transaction = Database.Session.BeginTransaction())
  {
    var employees = Database.Session.Query<Employee>()
    .Where(e => e.ResidentialAddress.City == "London");

    foreach (var employee in employees)
    {
      foreach (var benefit in employee.Benefits)
...
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Learning NHibernate 4
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