EntityFramework之一对多关系（三）

上篇介绍了一对一关系，下面介绍下一对多关系代码编写。

1、新建model实体，Product是产品类，Order是订单，一个产品对应多个订单

     public class Product
     {
         public int Id { get; set; }
         public string Name { get; set; }
         public string Description { get; set; }

         public virtual ICollection<Order> Orders { get; set; }
     }

     public class Order
     {
         public int Id { get; set; }
         public int ProductId { get; set; }
         public DateTime Date { get; set; }
         public string ShippingAddress { get; set; }

         public virtual Product Product { get; set; }
     }

2、创建一个EntityContext并继承自DbContext

     public class EntityContext : DbContext
     {
         public EntityContext()
             : base("name=DBConnectionString")
         {

         }

         public DbSet<Product> Product { get; set; }
         public DbSet<Order> Order { get; set; }

         protected override void OnModelCreating(DbModelBuilder modelBuilder)
         {
             modelBuilder.Configurations.AddFromAssembly(Assembly.GetExecutingAssembly());
             base.OnModelCreating(modelBuilder);
         }
     }

3、在web.config文件中添加数据库连接字符串

   <connectionStrings>
     <add name="DBConnectionString" connectionString="Data Source=.;Initial Catalog=OneToMany;Integrated Security=true" providerName="System.Data.SqlClient" />
   </connectionStrings>

4、接着创建实体映射

     public class ProductMap : EntityTypeConfiguration<Product>
     {
         public ProductMap()
         {
             ToTable("Product");
             HasKey(p => p.Id);
             //这个同OrderMap中注释语句效果一样,默认是级联
             HasMany(p => p.Orders).WithRequired(o => o.Product).HasForeignKey(o => o.ProductId).WillCascadeOnDelete(false);
         }
     }

     public class OrderMap : EntityTypeConfiguration<Order>
     {
         public OrderMap()
         {
             ToTable("Order");
             HasKey(o => o.Id);
             //WillCascadeOnDelete：不使用级联删除
             //HasRequired(o => o.Product).WithMany(p => p.Orders).HasForeignKey(o => o.ProductId).WillCascadeOnDelete(false);
         }
     }

5、我们写一些操作，让Code First生成数据库并验证数据是否新增

     EntityContext db = new EntityContext();
     var product = new Product() { Description = "电器", Name = "电磁炉" };
     db.Set<Product>().Add(product);
     db.SaveChanges();

     var order = new Order() { Date = DateTime.Now, ProductId = product.Id, ShippingAddress = "江西南昌" };
     db.Set<Order>().Add(order);
     db.SaveChanges();

     //表连接
     var list = db.Set<Product>().Include("Orders").ToList();

6、数据库关系图