Entity Framework Core Cookbook - Second Edition

Table of Contents

Entity Framework Core Cookbook - Second Edition

Credits

About the Author

About the Reviewer

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Why subscribe?

Preface

What this book covers

What you need for this book

Who this book is for

Sections

Getting ready

How to do it…

How it works…

There's more…

See also

Conventions

Reader feedback

Customer support

Downloading the example code

Errata

Piracy

Questions

1. Improving Entity Framework in the Real World

Introduction

Improving Entity Framework by using a code-first approach

Getting ready

How to do it…

How it works…

There's more…

Convention over configuration

Model-View-Controller

Single Responsibility Principle

Provider Model

Testing

See also

Unit testing and mocking

Getting ready

How to do it…

How it works…

There's more…

One class under test

Integration tests

Arrange, Act, Assert

Mocking

Creating databases from code

Getting ready

How to do it…

How it works…

There's more…

See also

Creating mock database connections

How to do it…

How it works…

See also

Implementing the repository pattern

Getting ready

How to do it…

How it works…

There's more…

Dependency Inversion Principle

Repository and caching

Mocking

Where generic constraint

See also

Implementing the unit of work pattern

Getting ready

How to do it…

How it works…

There's more…

Call per change

Interface Segregation Principle

Refactoring

See also

2. Mapping Entities

Introduction

Mapping non-public members

Getting ready

How to do it…

How it works…

There's more…

See also

Mapping interfaces

Getting ready

How to do it…

How it works…

See also

Shadow properties

Getting ready

How to do it…

How it works…

See also

Creating one-to-one maps

Getting ready

How to do it…

How it works…

There's more…

See also

Creating one-to-many maps

Getting ready

How to do it…

How it works…

There's more…

See also

Creating many-to-many maps

Getting ready

How to do it…

How it works…

There's more…

See also

Creating custom conventions

Getting ready

How to do it…

How it works…

There's more…

See also

Using sequence key generators

Getting ready

How to do it…

How it works...

There's more…

See also

Using GUIDs as keys

Getting ready

How to do it…

How it works…

There's more…

See also

Implementing inheritance – Table per Class hierarchy

Getting ready

How to do it…

How it works…

There's more…

3. Validation and Changes

Introduction

Validating simple properties

Getting ready

How to do it…

How it works…

There's more…

See also

Validating the whole entity

Getting ready

How to do it…

How it works…

See also

Validating groups of entities

How to do it…

How it works…

See also

Intercepting saving changes

Getting ready

How to do it…

How it works…

See also

Intercepting property changes

Getting ready

How to do it…

How it works…

See also

Setting the state of an entity

Getting ready

How to do it…

How it works…

There's more…

See also

Improving MVC UI with entity framework validation

Getting ready

How to do it…

How it works…

There's more…

Understanding the HTML helper

See also

Inserting, updating, and deleting entities with stored procedures

Getting ready

How to do it…

How it works…

There's more…

See also

Updating the database from model changes

Getting ready

How to do it…

How it works…

There's more…

See also

Dumping the SQL script for the database creation

Getting ready

How to do it…

How it works…

There's more…

See also

4. Transactions and Concurrency Control

Introduction

Using explicit transactions

Atomic

Consistent

Isolation

Durability

Getting ready

How to do it…

How it works…

See also

Using transactions in custom SQL operations

Getting ready

How to do it…

How it works…

There's more…

See also

Implementing optimistic concurrency in SQL Server

Getting ready

How to do it…

How it works…

There's more…

Database wins

Client wins/last one wins

See also

Implementing optimistic concurrency in a database-agnostic way

Getting ready

How to do it…

How it works…

There's more…

See also

5. Querying

Introduction

Executing client-side functions in LINQ queries

Getting ready

How to do it…

How it works…

See also

Mixing SQL with LINQ queries

Getting ready

How to do it…

How it works…

There's more…

See also

Getting entities from the local cache

Getting ready

How to do it…

How it works…

There's more…

See also

Creating filtered collections

Getting ready

How to do it…

How it works…

There's more…

See also

Creating reusable queries

Getting ready

How to do it…

How it works…

There's more…

Extension methods

Naming conflict

See also

Querying shadow properties

Getting ready

How to do it…

How it works…

There's more…

See also

Implementing the query object pattern

Getting ready

How to do it…

How it works…

There's more…

See also

Using dynamic LINQ

Getting ready

How to do it…

How it works…

There's more…

6. Advanced Scenarios

Introduction

Generating entities from the database

Getting ready

How to do it…

How it works…

There's more…

Implementing multitenancy

Getting ready

How to do it…

How it works…

There's more…

Strongly typed bulk operations

Getting ready

How to do it…

How it works…

There's more…

Handling soft deletes

Getting ready

How to do it…

How it works…

See also

Adding logging

Getting ready

How to do it…

How it works…

There's more…

Capturing the audit data

Getting ready

How to do it…

How it works…

See also

Retrieving entity metadata

Getting ready

How to do it…

How it works…

There's more…

See also

Improving MVC applications

Getting ready

How to do it.…

See also

Hooking infrastructure services

Using other databases

How to do it…

7. Performance and Scalability

Introduction

Improving the performance of queries

Getting ready

How to do it…

Modifications

Updates

Deletes

Queries

SQL

LINQ

See also

Testing and profiling queries

How to do it…

Logging

Database profiler

Real time monitoring

Testing

See also

Using asynchronous operations

Getting ready

How to do it…

Queries

Modifications

See also

Eager loading

Getting ready

How to do it…

How it works…

See also

Using the cache

Getting ready

How to do it…

How it works…

There's more…

A. Pitfalls

Introduction

GroupBy executes on the client side

Problem

How to fix it…

Table per class hierarchy requires nullable columns for derived classes

Problem

How to solve it…

References not eagerly fetched are lost

Problem

How to solve it…

Date/time operations are not supported

Problem

How to solve it…

Paging in SQL Server earlier than 2012

Problem

How to solve it…

Database null semantics

Problem

How to solve it…

Migrations and contexts with parameterized constructors

Problem

How to solve it…

Migrations with contexts in different projects

Problem

How to solve it…

Accessing the service provider too soon

Problem

How to solve it…

Setting the maximum string length

Problem

How to solve it…

Mapping discriminator columns

Problem

How to solve it…

Composite primary keys

Problem

How to solve it…

Refreshing entities

Problem

How to solve it…

Cascading entity deletes

Problem

How to solve it…

Index

Entity Framework Core Cookbook - Second Edition

Entity Framework Core Cookbook - Second Edition

Copyright © 2016 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: March 2012

Second edition: November 2016

Production reference: 1031116

Published by Packt Publishing Ltd.

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Birmingham B3 2PB, UK.

ISBN 978-1-78588-330-9

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Credits

Author

Ricardo Peres

Reviewer

Jason De Oliveira

Commissioning Editor

Kunal Parikh

Acquisition Editor

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Content Development Editors

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About the Author

Ricardo Peres is a Portuguese developer, blogger, and occasionally an e-book author. He has more than 17 years of experience in software development, using technologies such as C/C++, Java, JavaScript, and .NET. His interests include distributed systems, architectures, design patterns, and general .NET development.

He currently works for London-based Simplifydigital as a technical evangelist, and was first awarded as MVP in 2015.

Ricardo maintains a blog, Development With A Dot, where he regularly writes about technical issues. You can read it here: http://weblogs.asp.net/ricardoperes.

He has reviewed Learning NHibernate 4 for Packt.

You can catch up with him at @RJPeres75.

I'd like to thank my family, Zézinha, Francisco, and Madalena, for their love and patience and my friends and colleagues at Simplifydigital for all their support.

This book is dedicated to my parents, Irene (1947-2005) and Jorge Peres (1941-2015), with love and saudades.

About the Reviewer

Jason De Oliveira works as a CTO for MEGA International (http://www.mega.com), a software company in Paris (France) that provides modeling tools for enterprise architecture, enterprise governance risk, and compliance management. He is an experienced manager and senior solutions architect with a lot of skills in software architecture and enterprise architecture.

He loves sharing his knowledge and experience via his blog, by speaking at conferences, writing technical books, writing articles in the technical press, giving software courses as MCT, and coaching co-workers in his company. He frequently collaborates with Microsoft, and you can quite often find him at the Microsoft Technology Center (MTC) in Paris. Microsoft awarded him in 2011 with an MVP in C# for his numerous contributions to the Microsoft community. Microsoft seeks to recognize the best and brightest from technology communities around the world with the MVP award. These exceptional and highly-respected individuals come from more than 90 countries, serve their local online and offline communities, and have an impact worldwide. Jason is very proud to be one of them. Please feel free to contact him via his blog (http://www.jasondeoliveira.com) if you need any technical assistance or want to discuss technical subjects.

Jason has worked as a reviewer on .NET 4.5 Expert Programming Cookbook, WCF 4.5 Multi-tier Services Development with LINQ to Entities, .NET 4.5 Parallel Extensions Cookbook, and WCF 4.5 Multi-layer Services Development with Entity Framework, Third Edition by Packt. He has also worked as an author on Visual Studio 2013: Concevoir, développer et gérer des projets Web, les gérer avec TFS 2013 by Editions ENI.

I would like to thank my lovely wife, Orianne, and my beautiful daughters, Julia and Léonie, for supporting me in my work and for accepting long days and short nights during the week and sometimes even during the weekend. My life would not be the same without them!

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Preface

This book is about the new Entity Framework Core 1.0. In here, you will find recipes that will hopefully make your life easier when working with Entity Framework Core. If all goes well, you will also have some fun while doing it.

It has something for both beginners as well as more seasoned developers.

What this book covers

Chapter 1, Using Entity Framework in the Real World, introduces you to the structure of the sample project, and we will see some examples of how to use Entity Framework in a real MVC application.

Chapter 2, Mapping Entities, presents the way to configure the mapping of entities and properties and relations between entities.

Chapter 3, Validation and Changes, talks about how Entity Framework detects modifications made to entities, and how we can intercept those modifications, or apply our custom validation logic to it.

Chapter 4, Transactions and Concurrency Control, covers ACID transactions and optimistic concurrency control.

Chapter 5, Querying, covers the many querying options available to Entity Framework Core, some of which are quite new.

Chapter 6, Advanced Scenarios, presents some more advanced scenarios.

Chapter 7, Performance and Scalability, introduces you to some tips related to how we can make our application more responsive and scalable.

Appendix, Pitfalls, presents a list of pitfalls, or anti-patterns, regarding Entity Framework Core usage.

What you need for this book

All you need is .NET Core, including Entity Framework Core, together with an edition of Visual Studio 2015 that supports it (the free Community Edition will work).

We will be using SQL Server as the relational database (any version starting with 2012 will do, in any edition), including Express.

Who this book is for

This book is for .NET developers who work with relational databases on a daily basis and understand the basics of Entity Framework, but now want to use it in a more efficient manner. You are expected to have some prior knowledge of Entity Framework.

Sections

In this book, you will find several headings that appear frequently (Getting ready, How to do it, How it works, There's more, and See also).

To give clear instructions on how to complete a recipe, we use these sections as follows:

Getting ready

This section tells you what to expect in the recipe, and describes how to set up any software or any preliminary settings required for the recipe.

How to do it…

This section contains the steps required to follow the recipe.

How it works…

This section usually consists of a detailed explanation of what happened in the previous section.

There's more…

This section consists of additional information about the recipe in order to make the reader more knowledgeable about the recipe.

See also

This section provides helpful links to other useful information for the recipe.

Conventions

In this book, you will find a number of text styles that distinguish between different kinds of information. Here are some examples of these styles and an explanation of their meaning.

Code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles are shown as follows: Create an entity with the name MyEntity in the BusinessLogic project.

A block of code is set as follows:

namespace BusinessLogic

{

  public class Post : BlogContent

  {

    public string Body { get; set; }

  }

}

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

namespace BusinessLogic

{

  public class Post : BlogContent

  {

public string Body { get; set; }

  }

}

New terms and important words are shown in bold. Words that you see on the screen, for example, in menus or dialog boxes, appear in the text like this: "Open Using EF Core Solution from the included source code examples.

Note

Warnings or important notes appear in a box like this.

Tip

Tips and tricks appear like this.

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Chapter 1. Improving Entity Framework in the Real World

In this chapter, we will cover the following topics:

Improving Entity Framework by using a code-first approach

Unit testing and mocking

Creating databases from code

Creating mock database connections

Implementing the repository pattern

Implementing the unit of work pattern

Introduction

If we were to buy the materials to build a house, would we buy the bare minimum to get four walls up and a roof, without a kitchen or a bathroom? Or would we buy enough material to build the house with multiple bedrooms, a kitchen, and multiple bathrooms?

The problem lies in how we define the bare minimum. The progression of software development has made us realize that there are ways of building software that do not require additional effort, but reap serious rewards. This is the same choice we are faced with when we decide on the approach to take with Entity Framework. We could just get it running and it would work most of the time.

Customizing and adding to it later would be difficult, but doable. There are a few things that we would need to give up for this approach. The most important among those is control over how the code is written. We have already seen that applications grow, mature, and have features added. The only thing that stays constant is the fact that at some point in time, in some way, we will come to push the envelope of almost every tool that we leverage to help us. The other side is that we could go into development, being aware of the value-added benefits that cost nothing, and with that knowledge, avoid dealing with unnecessary constraints.

When working with Entity Framework, there are some paths and options available to us. There are two main workflows for working with Object-Relational Mapper (ORM) tools such as Entity Framework:

Database first: We start by defining our database objects and their relations, then write our classes to match them, and we bind them together

Code first: We start by designing our classes as Plain Old CLR Objects (POCOs) to model the concepts that we wish to represent, without caring (too much!) how they will be persisted in the database

Note

The model-first approach was dropped in Entity Framework Core 1.0.

While following the database-first approach, we are not concerned with the actual implementation of our classes, but merely the structures—tables, columns, keys—on which they will be persisted. In contrast, with POCOs or code first, we start by designing the classes that will be used in our programs to represent the business and domain concepts that we wish to model. This is known as Domain-Driven Design (DDD). DDD certainly includes code first, but it is much more than that.

All of these approaches will solve the problem with