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