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

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 = new Product() { Name = "腐竹", Code = "002", Price = 3, Count = 100, Unit = "g", LastUpdateTime = DateTime.Now };
                ctx.Products.Add(p1);

                Sale s1 = new Sale() { Price = 5, Count = 10, TotalPrice = 50, ActualPrice = 50, CreateTime = DateTime.Now,Product=p1 };
                ctx.Sales.Add(s1);
                ctx.SaveChanges();
            }