EF CodeFirst Mirgration

新建类库Models，加入以下三个类：

Product：

public class Product
    {
        /// <summary>
        /// 编号
        /// </summary>
        public int Id { get; set; }
        /// <summary>
        /// 名称
        /// </summary>
        public string Name { get; set; }
        /// <summary>
        /// 型号
        /// </summary>
        public string Code { get; set; }
        /// <summary>
        /// 单价
        /// </summary>
        public double Price { get; set; }
        /// <summary>
        /// 单位
        /// </summary>
        public string Unit { get; set; }
        /// <summary>
        /// 数量
        /// </summary>
        public double Count { get; set; }
        /// <summary>
        /// 最后更新时间
        /// </summary>
        public DateTime LastUpdateTime { get; set; }
    }

Purchase：

public class Purchase
    {
        /// <summary>
        /// 编号
        /// </summary>
        public int Id { get; set; }
        /// <summary>
        /// 产品编号
        /// </summary>
        public int ProductId { get; set; }
        /// <summary>
        /// 单价
        /// </summary>
        public double Price { get; set; }
        /// <summary>
        /// 数量
        /// </summary>
        public double Count { get; set; }
        /// <summary>
        /// 总价
        /// </summary>
        public double TotalPrice { get; set; }
        /// <summary>
        /// 实际总价
        /// </summary>
        public double ActualPrice { get; set; }
        /// <summary>
        /// 创建时间
        /// </summary>
        public DateTime CreateTime { get; set; }
        public virtual Product Product { get; set; }
    }

Sale：

public class Sale
    {
        /// <summary>
        /// 编号
        /// </summary>
        public int Id { get; set; }
        /// <summary>
        /// 产品编号
        /// </summary>
        public int ProductId { get; set; }
        /// <summary>
        /// 单价
        /// </summary>
        public double Price { get; set; }
        /// <summary>
        /// 数量
        /// </summary>
        public double Count { get; set; }
        /// <summary>
        /// 总价
        /// </summary>
        public double TotalPrice { get; set; }
        /// <summary>
        /// 实际总价
        /// </summary>
        public double ActualPrice { get; set; }
        /// <summary>
        /// 创建时间
        /// </summary>
        public DateTime CreateTime { get; set; }
        public virtual Product Product { get; set; }
    }

通过nuget引入EF:

install-package entityframework

在单元测试或者应用程序中也引入EF，在App.config或Web.config中会自动加入EF的配置：

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <configSections>
    <!-- For more information on Entity Framework configuration, visit http://go.microsoft.com/fwlink/?LinkID=237468 -->
    <section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
  </configSections>
  <connectionStrings>
    <add name="SalesDB" connectionString="server=.;database=SalesDB;uid=sa;pwd=pwd;" providerName="System.Data.SqlClient"/>
  </connectionStrings>
  <entityFramework>
    <defaultConnectionFactory type="System.Data.Entity.Infrastructure.LocalDbConnectionFactory, EntityFramework">
      <parameters>
        <parameter value="mssqllocaldb" />
      </parameters>
    </defaultConnectionFactory>
    <providers>
      <provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
    </providers>
  </entityFramework>
</configuration>

在connectionStrings节点中添加数据库连接

新建DBContext类：

    public class SalesContext : DbContext
    {
        public SalesContext() : base("name=SalesDB")
        {
            Database.SetInitializer(new MigrateDatabaseToLatestVersion<SalesContext, Models.Migrations.Configuration>("SalesDB"));
        }
        public DbSet<Product> Products { get; set; }
        public DbSet<Purchase> Purchases { get; set; }
        public DbSet<Sale> Sales { get; set; }
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            base.OnModelCreating(modelBuilder);
        }
    }

"name=SalesDB"表示使用config中配置的连接

Database.SetInitializer(new MigrateDatabaseToLatestVersion<SalesContext, Models.Migrations.Configuration>("SalesDB"));

开启自动迁移到最新版本，这样不会删除原有表和数据

在程序包管理控制台中输入：enable-migrations –EnableAutomaticMigration:$true，即可开启自动迁移。

当然也可以手动迁移，需要用到下面命令：

enable-migrations

会在Models中的Migrations目录中自动生成201603290414524_InitialCreate.cs

Add-migration

add-migration PurchaseChange   需要输入迁移的名称

会在Models中的Migrations目录中自动生成201603300705373_PurchaseChange.cs

Update-database

update-database –verbose可以看到迁移的代码

这里需要注意的是如果数据库中已有相同的表，再开启自动迁移的话会提示错误，这是只需把InitialCreate.cs删除再update-database即可

如果属性名为 Id 或 <类名>Id. Code-First 会自动以此创建主键.主键可以是任意类型, 如果主键是数字型或者GUID,会配置成自动增长或自动生成.

但如果像下面这样定义类的话就会报错：

public class Product
{public int PId { get; set; }
    public string Name { get; set; }
}
        

在Purchases类中，定义了Product的关联，

public int ProductId { get; set; }
public virtual Product Product { get; set; }

EF会自动为在Purchases中创建ProductId 外键：

在迁移代码中可以看到：

    public partial class PurchaseChange : DbMigration
    {
        public override void Up()
        {
            CreateIndex("dbo.Purchases", "ProductId");
            AddForeignKey("dbo.Purchases", "ProductId", "dbo.Products", "Id", cascadeDelete: true);
        }
 
        public override void Down()
        {
            DropForeignKey("dbo.Purchases", "ProductId", "dbo.Products");
            DropIndex("dbo.Purchases", new[] { "ProductId" });
        }
    }

Sales类也添加了ProductId的外键，这样在创建Sale时如果新增Product的话，会自动把新增Product的Id赋值到Sale里的ProductId上：

using (var ctx = new SalesContext())
            {
                Product p1 = , Count = , Unit = "g", LastUpdateTime = DateTime.Now };
                ctx.Products.Add(p1);
 
                Sale s1 = , Count = , TotalPrice = , ActualPrice = , CreateTime = DateTime.Now,Product=p1 };
                ctx.Sales.Add(s1);
                ctx.SaveChanges();
            }

怎么进行多表查询呢？

public class Student
    {
        public Student()
        {
 
        }
        public int StudentID { get; set; }
        public string StudentName { get; set; }
        public DateTime? DateOfBirth { get; set; }
        public byte[] Photo { get; set; }
        public decimal Height { get; set; }
        public float Weight { get; set; }
        public int TeacherId { get; set; }
        public int StandardId { get; set; }
    }

public class Teacher
    {
        public Teacher()
        {
 
        }
        public int TeacherId { get; set; }
        public string TeacherName { get; set; }
    }

public class Standard
    {
        public Standard()
        {
 
        }
        public int StandardId { get; set; }
        public string StandardName { get; set; }
    }

这里没有定义表的外键，要查询的时候可以如下查询：

public class StudentViewModel
    {
        public int StudentID { get; set; }
        public string StudentName { get; set; }
 
        public string StandardName { get; set; }
        public string TeacherName { get; set; }
    }

var stu = from u in ctx.Students
                          join da in ctx.Standards on u.StandardId equals da.StandardId
                          join ta in ctx.Teachers on u.TeacherId equals ta.TeacherId
                          select new StudentViewModel()
                          {
                              StudentID = u.StudentID,
                              StudentName = u.StudentName,
                              StandardName = da.StandardName,
                              TeacherName = ta.TeacherName
                          };
                var stuview = stu.FirstOrDefault();