6. Let's Retrieve Some Data from the Database | Learning NHibernate 4

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Table Of Contents

Learning NHibernate 4

By : Suhas H Chatekar

3.6 (9)

Learning NHibernate 4

3.6 (9)

By: Suhas H Chatekar

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.

Preface

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Free Chapter

1. Introduction to NHibernate

1. Introduction to NHibernate

What is ORM?

What is NHibernate?

What is new in NHibernate 4.0?

NHibernate for users of Entity Framework

Is using ORM a bad idea?

Building blocks of NHibernate

Summary

2. Let's Build a Simple Application

2. Let's Build a Simple Application

Explaining the approach used in learning NHibernate

The problem statement

The development setup

The domain model

Adding some code

Summary

3. Let's Tell NHibernate About Our Database

3. Let's Tell NHibernate About Our Database

Important NHibernate terminology

Mapping the prerequisites

Different mechanisms to write the mappings

XML mappings for the Employee class

Identifier generation

Mapping associations

Mapping inheritance

Mapping components

Mapping by code

Fluent mapping a.k.a. Fluent NHibernate

Choosing the right mapping method

Summary

4. NHibernate Warm-up

4. NHibernate Warm-up

Warming up NHibernate succinctly

The NHibernate session architecture

XML configuration

Programmatic configuration

Loquacious configuration

Fluent configuration

Configuration options

Generating the database scripts from mappings

Summary

5. Let's Store Some Data into the Database

5. Let's Store Some Data into the Database

Entity states

Transactions and unit of work

Saving entities

Transitive persistence using cascade styles

Transitive persistence/cascading in action

Bidirectional associations and ownership

Order of operations

Entity equality

The architecture diagram

Summary

6. Let's Retrieve Some Data from the Database

6. Let's Retrieve Some Data from the Database

Querying the workflow

Different querying methods

Joins

Lazy loading

Eager fetching

Pagination and ordering of results

Retrieving entities by identifiers

Polymorphic queries

Summary

7. Optimizing the Data Access Layer

7. Optimizing the Data Access Layer

Baseline and optimize

Organization of the chapter

Batching

Fetching strategies

Avoiding the select N+1 problem

Avoiding eager fetching

Using extra-lazy for lazy collections

Summary

8. Using NHibernate in a Real-world Application

8. Using NHibernate in a Real-world Application

What kind of application are we building?

Architectural principles we will follow

Feature 1 – onboarding an employee

Unit of work

Feature 2 – updating the details of an employee

Feature 3 – searching employees

Summary

9. Advanced Data Access Patterns

9. Advanced Data Access Patterns

Problems with the repository pattern

Specification pattern

Query object pattern

Summary

10. Working with Legacy Database

10. Working with Legacy Database

Composite IDs

Components

Join-mapping to load data from multiple tables

Working with database views

Using subselect instead of views

Working with stored procedures

Using custom DTOs

Summary

11. A Whirlwind Tour of Other NHibernate Features

11. A Whirlwind Tour of Other NHibernate Features

Concurrency control

Event system

Caching

Stateless sessions

User-defined types

Summary

Index

Index

Querying the workflow

NHibernate supports different ways of retrieving data from database. The basic semantics of writing a NHibernate query is no different than that of a standard SQL query which consists of the following three main parts:

You specify which tables are involved in query
You specify an optional filter using WHERE statement
You specify which columns you want to return using SELECT statement

There are other optional things you can add to a SQL query such as ordering, grouping, pagination, and so on, which is also supported by NHibernate. Queries written in NHibernate fundamentally differ from standard SQL queries on one aspect – composability. A query is represented by a query object. You can compose a query object by incrementally adding constructs such as joins with more tables, ordering, the where clauses, and so on. When you have finished building the query object, you call one of the terminal method on it, such as List<T> or First<T> which will tell NHibernate...

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