Entity Framework Core Cookbook

Entity Framework Core Cookbook - Second Edition

By : Ricardo Peres

Buy this Book

Entity Framework Core Cookbook - Second Edition

By: Ricardo Peres

Buy this Book

Overview of this book

Entity Framework is a highly recommended Object Relation Mapping tool used to build complex systems. In order to survive in this growing market, the knowledge of a framework that helps provide easy access to databases, that is, Entity Framework has become a necessity. This book will provide .NET developers with this knowledge and guide them through working efficiently with data using Entity Framework Core. You will start off by learning how to efficiently use Entity Framework in practical situations. You will gain a deep understanding of mapping properties and find out how to handle validation in Entity Framework. The book will then explain how to work with transactions and stored procedures along with improving Entity Framework using query libraries. Moving on, you will learn to improve complex query scenarios and implement transaction and concurrency control. You will then be taught to improve and develop Entity Framework in complex business scenarios. With the concluding chapter on performance and scalability, this book will get you ready to use Entity Framework proficiently.

Entity Framework Core Cookbook - Second Edition

Credits

About the Author

About the Reviewer

www.PacktPub.com

Preface

Free Chapter

Improving Entity Framework in the Real World

Introduction

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

Mapping Entities

Introduction

Mapping non-public members

Mapping interfaces

Shadow properties

Creating one-to-one maps

Creating one-to-many maps

Creating many-to-many maps

Creating custom conventions

Using sequence key generators

Using GUIDs as keys

Implementing inheritance – Table per Class hierarchy

Validation and Changes

Introduction

Validating simple properties

Validating the whole entity

Validating groups of entities

Intercepting saving changes

Intercepting property changes

Setting the state of an entity

Improving MVC UI with entity framework validation

Inserting, updating, and deleting entities with stored procedures

Updating the database from model changes

Dumping the SQL script for the database creation

Transactions and Concurrency Control

Introduction

Using explicit transactions

Using transactions in custom SQL operations

Implementing optimistic concurrency in SQL Server

Implementing optimistic concurrency in a database-agnostic way

Querying

Introduction

Executing client-side functions in LINQ queries

Mixing SQL with LINQ queries

Getting entities from the local cache

Creating filtered collections

Creating reusable queries

Querying shadow properties

Implementing the query object pattern

Using dynamic LINQ

Advanced Scenarios

Introduction

Generating entities from the database

Implementing multitenancy

Strongly typed bulk operations

Handling soft deletes

Adding logging

Capturing the audit data

Retrieving entity metadata

Improving MVC applications

Hooking infrastructure services

Using other databases

Performance and Scalability

Introduction

Improving the performance of queries

Testing and profiling queries

Using asynchronous operations

Eager loading

Using the cache

Pitfalls

Introduction

GroupBy executes on the client side

Table per class hierarchy requires nullable columns for derived classes

References not eagerly fetched are lost

Date/time operations are not supported

Paging in SQL Server earlier than 2012

Database null semantics

Migrations and contexts with parameterized constructors

Migrations with contexts in different projects

Accessing the service provider too soon

Setting the maximum string length

Mapping discriminator columns

Composite primary keys

Refreshing entities

Cascading entity deletes

Index

Customer Reviews

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Refreshing entities

Because of the first level cache, reloading an entity with modified database values will not refresh it.

Problem

Entity Framework Core, like other Object-Relational Mappers, uses something called a First Level Cache (also known as Identity Map) to keep track of the entities that it knows about. These are entities that were loaded from the database or ones that have been marked for persistence. This, in general, can be regarded as an optimization: when Entity Framework loads the same record over and over again, it does not need to instantiate the entity's class and hydrate it with the values coming from the database.

The problem is, what if the entity's record changes in the database and we wish to refresh the ones we have? For example, this won't work:

//retrieve an entity from the database
var myEntity = ctx.MyEntities.First();
//the entity's record changes in the database
//retrieve the entity again
//unchanged: is returned from the first level cache
myEntity = ctx.MyEntities.First();

How to solve it…

The way to solve this is to first detach it from the context, which effectively means removing it from the first level cache, like this:

//retrieve an entity from the database
var myEntity = ctx.MyEntities.First();
//the entity's record changes in the database
//detach the entity
ctx.Entry(myEntity).State = EntityState.Detached;
//retrieve the entity again
myEntity = ctx.MyEntities.First();

This way, you are sure to get the most up-to-date values.

Entity Framework Core Cookbook - Second Edition

By : Ricardo Peres

Entity Framework Core Cookbook - Second Edition

By: Ricardo Peres

Overview of this book

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Current Title:

Entity Framework Core Cookbook - Second Edition

Refreshing entities

Problem

How to solve it…