Entity Framework Code First入门：快速掌握与设计驱动开发

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《Entity Framework Code First Succinctly》是由Ricardo Peres编著，Syncfusion公司于2014年发行的一本关于微软旗舰数据访问技术——Entity Framework Code First（简称EFCF）的教程书籍。该书旨在帮助开发者理解和掌握对象关系映射（ORM）在OOP（面向对象编程）与关系数据库之间的桥梁作用，尤其是在EFCF的领域驱动设计（DDD）方法中。 EFCF是经典的Entity Framework的后续版本，自2009年起就存在，它提供了两种开发模式：数据库第一和模型第一。数据库第一基于现有数据库生成代码，而模型第一则是先定义概念模型，然后根据此模型生成数据库和代码。EFCF则采取了新的策略，即从代码出发，通过代码生成数据库，这种方式更符合DDD的理念，也具有更简单、易用的API。 EFCF受到广泛关注的原因包括： 1. **快速入门**：通过NuGet包管理器即可轻松安装，无需复杂的配置。 2. **简洁易用**：避免了XML schema、基类继承和繁琐接口的困扰，开发者只需专注于业务领域模型，而将持久化细节留给框架处理。 3. **平台支持**：基于强大的数据库访问API，微软对其后续发展给予持续关注和支持。 4. **频繁更新**：由于不受.NET框架发布周期限制，EFCF的新版本发布更为频繁。 5. **社区参与**：Microsoft公开源代码并接受社区反馈，提高了bug修复速度和新功能的采纳，让用户能尽早体验改进。对于熟悉经典Entity Framework的开发者来说，EFCF意味着需要亲手编写实体类，没有图形化设计工具，但这实际上提供了更大的灵活性，允许开发者更好地控制生成的代码。《Entity Framework Code First Succinctly》是一本实用指南，适合那些希望深入理解EFCF的开发人员，无论你是初学者还是希望提升技能的专家，都能从中获得有关ORM、DDD和Microsoft官方数据访问技术的深入洞察。

Core Concepts

Before a class model can be used to query a database or to insert values into it, Entity

Framework needs to know how it should translate code (classes, properties, and instances)

back and forth into the database (specifically, tables, columns and records). For that, it uses a

mapping, for which two APIs exist. More on this later, but first, some fundamental concepts.

Contexts

A context is a class that inherits from DbContext and which exposes a number of entity

collections in the form of DbSet<T> properties. Nothing prevents you from exposing all entity

types, but normally you only expose aggregate roots, because these are the ones that make

sense querying on their own.

An example context might be the following.

Tip: Do notice that both setters and getters for the entity collections are

public.

Note: Feel free to add your own methods, business or others, to the context

class.

The DbContext class offers a number of constructors, mostly for configuring the connection

string:

 If the no-arguments constructor is called, the DbContext will assume that a connection

string with the same name as the context’s class will exist in the configuration file.

 There’s also a constructor that takes a single string parameter. This parameter will either

be a full connection string that is specific to the current database provider or a name of a

connection string that must be present in the configuration file.

 For the sake of completeness, another constructor exists that takes an existing

DbConnection; Entity Framework might not take full control of this connection, for

example, it won’t try to dispose of it when no longer needed.

public class ProjectsContext : DbContext

{

public DbSet<Tool> Tools { get; set; }

public DbSet<Resource> Resources { get; set; }

public DbSet<Project> Projects { get; set; }

public DbSet<Customer> Customers { get; set; }

public DbSet<Technology> Technologies { get; set; }

}

public class ProjectsContext : DbContext

{

public ProjectsContext() { }

public ProjectsContext(String nameOrConnectionString): base(nameOrConnectionString)

{ }

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