EFCore code first 創建數據庫

此處記錄學習efcore 過程中一些學習筆記：

      1.code first 創建數據庫，一對多關係對應爲一個對象擁有一個集合，這個集合使用virtual標識以便使用lazyLoading,另一方面被擁有的對象也有所屬對象及所屬對象ID。多對多關係除了兩個對象分別用擁有對方集合方式表示外，還得有兩個對象關係對象存儲關係所屬對象。類型關係展示如下所示：

一個Customer有多個訂單：

    public partial class Customers
    {
        public Customers()
        {
            Orders = new HashSet<Orders>();
        }

        [Key]
        public int Id { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string Address { get; set; }
        public string Phone { get; set; }
        public string Email { get; set; }

        [InverseProperty("Customer")]
        public virtual ICollection<Orders> Orders { get; set; }
    }

一個訂單order屬於一個Customer,並且一個訂單包含多個商品product

    public partial class Orders
    {
        public Orders()
        {
            ProductOrders = new HashSet<ProductOrders>();
        }

        [Key]
        public int Id { get; set; }
        public DateTime OrderPlaced { get; set; }
        public DateTime? OrderFulfilled { get; set; }
        public int CustomerId { get; set; }

        [ForeignKey(nameof(CustomerId))]
        [InverseProperty(nameof(Customers.Orders))]
        public virtual Customers Customer { get; set; }
        [InverseProperty("Order")]
        public virtual ICollection<ProductOrders> ProductOrders { get; set; }
    }

一個商品product分佈在多個訂單中:

    public partial class Products
    {
        public Products()
        {
            ProductOrders = new HashSet<ProductOrders>();
        }

        [Key]
        public int Id { get; set; }
        [Required]
        public string Name { get; set; }
        [Column(TypeName = "decimal(18, 2)")]
        public decimal Price { get; set; }

        [InverseProperty("Product")]
        public virtual ICollection<ProductOrders> ProductOrders { get; set; }
    }

此關係對象爲訂單，商品多對多關係對象：

    public partial class ProductOrders
    {
        [Key]
        public int Id { get; set; }
        public int Quantity { get; set; }
        public int ProductId { get; set; }
        public int OrderId { get; set; }

        [ForeignKey(nameof(OrderId))]
        [InverseProperty(nameof(Orders.ProductOrders))]
        public virtual Orders Order { get; set; }
        [ForeignKey(nameof(ProductId))]
        [InverseProperty(nameof(Products.ProductOrders))]
        public virtual Products Product { get; set; }
    }

 code first創建對象之後，得再創建DbContext對象，將那些是表給用DbSet<object>標識出來：

public class ContosoPetsContext:DbContext
    {
        public DbSet<Customer> Customers { get; set; }
        public DbSet<Order> Orders { get; set; }
        public DbSet<Product> Products { get; set; }
        public DbSet<ProductOrder> ProductOrders { get; set; }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseSqlServer(@"Data Source=(LocalDb)\MSSQLLocalDB;Initial Catalog=ContosoPets;Integrated Security=true");
        }
    }

之後用包管理控制檯輸入命令：Add-Migration InitialCreat 創建對象數據庫。之後Update-Database將更新到數據庫。加字段或者修改字段之後，執行Add-Migration AddOrModifyFiled進行同步更新到數據庫。