Entity Framework 實戰 – 多對多自我關聯 Many to Many , Self Referencing 模型實作 (二)

此篇文是 Entity Framework 實戰 – 多對多自我關聯 Many to Many , Self Referencing 模型實作 (一)的續篇 , 當我們把基本模型 Product Class 建立好後，我們開始實作一個繼承 DbContext 的子類別，在這邊你可以把 DbContext 當做是資料庫的層次意義角度來看待

新增一個Class 名為 ProductContext.cs

然後按【新增】按鈕，並在 ProductContext 宣示繼承 DbContext 類別，如以下程式碼

  1: using System;

  2: using System.Collections.Generic;

  3: using System.Data.Entity;

  4: using System.Linq;

  5: using System.Text;

  6: using System.Threading.Tasks;

  7: 

  8: namespace EF6_ManyToManyAndSelf

  9: {

 10:     public class ProductContext : DbContext

 11:     {

 12: 

 13:     }

 14: }
接著加入 DbSet<Product> 的宣告，用於表示 存放著 Product Table（Class）的集合清單
public DbSet<Product> Products; 
然後為了完成透過 Product 本身的 Class 來完成 多對多自身關聯，需要 override OnModelCreating Method , 程式碼如下

   1:   protected override void OnModelCreating(DbModelBuilder modelBuilder)
   2:          {
   3:              base.OnModelCreating(modelBuilder);
   4:   
   5:              modelBuilder.Entity<Product>()
   6:                          .HasMany(p => p.RelatedProducts)
   7:                          .WithMany(p => p.AboveProducts)
   8:                          .Map(m =>
   9:                                    {
  10:                                        m.MapLeftKey("ProductID");
  11:                                        m.MapRightKey("RelatedProductID");
  12:                                        m.ToTable("RelatedProduct");
  13:                                    }
  14:                          );
  15:          }

到這邊基本上已經完成 EntityFramework 的宣告….
然後讓我們在前端界面使用我們實作好的 ProductContext ，來看看如何使用….程式碼如下


   1:  using System;
   2:  using System.Collections.Generic;
   3:  using System.Linq;
   4:  using System.Text;
   5:  using System.Threading.Tasks;
   6:   
   7:  namespace EF6_ManyToManyAndSelf
   8:  {
   9:      class Program
  10:      {
  11:          static void Main(string[] args)
  12:          {
  13:              using (var context = new ProductContext())
  14:              {
  15:                  var product1 = new Product { ProductName = "美容業零售管理系統", Price = 59888M };
  16:                  var product2 = new Product { ProductName = "窗簾業ERP系統", Price = 3500000M };
  17:                  var product3 = new Product { ProductName = "玩具製造業ERP系統", Price = 6700000M };
  18:                  product2.RelatedProducts.Add(product3);
  19:                  product1.RelatedProducts.Add(product2);
  20:                  context.Products.Add(product1);
  21:                  context.SaveChanges();
  22:              }
  23:              using (var context = new ProductContext())
  24:              {
  25:                  var product2 = context.Products.First(p => p.ProductName == "窗簾業ERP系統");
  26:                  Console.WriteLine("Product: {0} ... {1}", product2.ProductName, product2.Price.ToString("C"));
  27:                  Console.WriteLine("Related Products");
  28:                  foreach (var prod in product2.RelatedProducts)
  29:                  {
  30:                      Console.WriteLine("\t{0} ... {1}", prod.ProductName, prod.Price.ToString("C"));
  31:                  }
  32:                  foreach (var prod in product2.AboveProducts)
  33:                  {
  34:                      Console.WriteLine("\t{0} ... {1}", prod.ProductName, prod.Price.ToString("C"));
  35:                  }
  36:              }
  37:   
  38:              Console.ReadKey();
  39:          }
  40:      }
  41:  }

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執行結果為
 

 
 
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網智數位-軟體開發（軟件開發）

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