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

巴特西

EntityFramework之一对多关系（三）

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