Entity Framework4.0 (三)概述(EF4 的Code First方法)

EF4支持三种构建方法：1. Database First方法。2.Model First方法。3.Code First 方法。开发人员可根据具体的项目情况，选择任一种方法。

上次快速演示了Model First的方法。这次演示Code First方法。

EF4.0引入CTP4可支持Code First了。Microsoft在EF4.1中引入EntityFramework4.1/4.2加强Code First的支持。（EF4.1的DataAnnotation, Fluent API 更完善，对POCO的支持更直接方便。关于EF4.1/4.2的使用，我在后面博文中我会补上的。）

在此，给出EF4.0的使用方法以快速演示：

首先，我们要下载并安装CTP4：URL http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=8812。

当安装完成CTP4后。（安装CTP4之前最好把Visual Studio2010关掉。）

1. 启动Visual Studio 2010.

2. 创建一个Console Application : 名称：EFCodeFirstWalkthrough

3. 在解决方案上右键，选择：添加一个类库项目：名称：EFCodeFirstWalkthroughModel。

4. 右键EFCodeFirstWalkthrough项目，添加.NET类库引用：Microsoft.Data.Entity.CTP; 添加.NET类库引用：System.Data.Entity.添加项目引用:EFCodeFirstWalkthroughModel.

5.在类库项目中添加类文件：Author.cs，Book.cs，Person.cs，Publisher.cs：代码如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace EFCodeFirstWalkthroughModel
{
    public class Author : Person
    {   
        public int AuthorId { get; set; }
        public virtual ICollection<Book> Books { get; set; }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace EFCodeFirstWalkthroughModel
{
    public class Book
    {
        public string ISBN { get; set; }
        public string Title { get; set; }
        public DateTime FirstPublished { get; set; }
        public bool IsFiction { get; set; }
        public virtual Publisher Publisher { get; set; }
        public virtual Author Author { get; set; }
    }    
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace EFCodeFirstWalkthroughModel
{
    public class Person
    {
        public int PersonId { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace EFCodeFirstWalkthroughModel
{
    public class Publisher
    {
        public int PublisherId { get; set; }
        public string Name { get; set; }
        public virtual ICollection<Book> Books { get; set; }
    }

}

6.在Cosole 项目EFCodeFirstWalkthrough 中添加类文件：BookCatalog.cs，BookConfiguration.cs ，并修改Program.cs 的代码。如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using EFCodeFirstWalkthroughModel;
using System.Data.Objects;
using System.Data.EntityClient;


namespace EFCodeFirstWalkthrough
{
    public class BookCatalog : ObjectContext
    {
        private ObjectSet<Book> _books;
        private ObjectSet<Person> _people;
        private ObjectSet<Publisher> _publishers;

        public BookCatalog(EntityConnection connection)
            : base(connection)
        { }

        public ObjectSet<Book> Books
        {
            get
            {
                return this._books == null
                    ? this._books = this.CreateObjectSet<Book>()
                    : this._books;
            }
        }
        
        public ObjectSet<Person> People     
        {
            get
            {
                return this._people == null
                    ? this._people = this.CreateObjectSet<Person>()
                    : this._people;
            }
        }  

        public ObjectSet<Publisher> Publishers
        {

            get
            {
                return this._publishers == null
                    ? this._publishers = this.CreateObjectSet<Publisher>()
                    : this._publishers;
            }
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.Entity.ModelConfiguration;

namespace EFCodeFirstWalkthroughModel
{
    public class BookConfiguration : EntityConfiguration<Book>
    {
        public BookConfiguration()
        {
            this.HasKey(b => b.ISBN);
            this.Property(b => b.Title).IsRequired();
            this.HasRequired(b => b.Author).WithMany(a => a.Books);
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using EFCodeFirstWalkthroughModel;
using System.Data.Entity.ModelConfiguration;
using System.Data.SqlClient;

namespace EFCodeFirstWalkthrough
{
    class Program
    {
        static void Main(string[] args)
        {
            var builder = new ModelBuilder();
            builder.Configurations.Add(new BookConfiguration());
            builder.Entity<Person>();
            builder.Entity<Publisher>().Property(p => p.Name).IsRequired().HasMaxLength(50);
            var model = builder.CreateModel();
            using (var connection = new SqlConnection(@"Server=.\SQLEXPRESS;Database=CodeFirstWalkthrough;Trusted_Connection=True;"))
            {
                using (var context = model.CreateObjectContext<BookCatalog>(connection))
                {
                    if (!context.DatabaseExists())
                    {
                        context.CreateDatabase();
                    }
                    var book = new Book
                    {
                        ISBN = "1111",
                        Title = "Intro to Code First",
                        FirstPublished = DateTime.Today,
                        IsFiction = false,
                        Author = new Author { FirstName = "Rowan", LastName = "Miller" },
                        Publisher = new Publisher { Name = "EF Books" }
                    };
                    context.Books.AddObject(book);
                    context.SaveChanges();
                }
            }
        }
    }
}

编译项目，执行。

然后观察数据库：会发现生成一个名为CodeFirstWalkthrough的数据库文件。并且在里面有数据表生成。

注意：在此项目演示过程中，我们并未指定SqlConnection所用的连接字符串，但是EF4会利用我们指定给SqlConnection的参数去生连接特定的数据库服务器，并生成数据库。

好了，Code First 先到这里吧。休息咯！！！