實體框架添加多個相關的實體與單個插入

Question

我有一個GenericService添加方法如下所示： -

public bool Add(T entity, Expression<Func<T, bool>> filter = null) 
    { 
     try 
     { 
      _genericRepository.Add(entity, filter); 
     } 
     catch (Exception e) 
     { 
      return false; 
     } 
     return true; 
    } 

和GenericRepository添加方法如下所示： -

public void Add(T entity, Expression<Func<T, bool>> filter = null) 
    { 
     var existing = Get<T>(filter); 
     if (existing.Result != null) return; 
     Context.Add(entity); 
     Save(); 
    } 

這是呼叫我我正在ProductsController中執行： -

[HttpPost] 
    public IActionResult Create([FromBody] Product product) 
    { 
     if (product == null) 
      return BadRequest(); 

     var result = _productsService.Add(product, m => m.Name == product.Name); 
     if (result) 
     { 
      return CreatedAtRoute("GetProducts", new { id = product.Id }, product); 

     } 
     return BadRequest("Item not added"); 
    } 

我正在通過集成測試的方式創建此文件作爲fo llows： -

 testBrand = new Brand { Name = "testBrand" }; 
     testImage = new Image { Name = "testImage", Url = "/Brands/adidas_logo_test.png" }; 
     testBrand.Image = testImage; 

     testCategory = new Category {Name = "testCategory"}; 

     testProduct = new Product 
     { 
      Category = testCategory, 
      Name = "testProduct", 
      Brand = testBrand, 
      BrandId = testBrand.Id, 
      CategoryId = testCategory.Id, 
      Deal = false, 
      Description = "testDescription", 
      Discount = "50% Discount", 
      Image = testImage, 
      ImageId = testImage.Id, 
      Price = new decimal(50.00), 
      Stock = 5 
     }; 

    [Test] 
    public async Task Create_CreateAProduct_NewBrandNewCategoryNewImageProductsController() 
    { 
     //Arrange 

     //Act 
     //create new image 
     var requestImage = "api/Images/"; 
     var postResponseImage = await _client.PostAsJsonAsync(requestImage, testImage); 
     var created = await postResponseImage.Content.ReadAsStringAsync(); 
     var createdImage = JsonConvert.DeserializeObject<Image>(created); 

     //Act 
     testBrand.Image = createdImage; 
     testBrand.ImageId = createdImage.Id; 
     testImage.Id = createdImage.Id; 

     var postResponseProduct = await _client.PostAsJsonAsync(requestProduct, testProduct); 
     var createdProduct = await postResponseProduct.Content.ReadAsStringAsync(); 
     var createdProductObj = JsonConvert.DeserializeObject<Product>(createdProduct); 

     var getResponse = await _client.GetAsync(requestProduct + "Get/" + createdProductObj.Id); 
     var fetched = await getResponse.Content.ReadAsStringAsync(); 
     var fetchedProduct = JsonConvert.DeserializeObject<Product>(fetched); 

     // Assert 
     Assert.IsTrue(postResponseProduct.IsSuccessStatusCode); 
     Assert.IsTrue(getResponse.IsSuccessStatusCode); 

     Assert.AreEqual(testProduct.Name, createdProductObj.Name); 
     Assert.AreEqual(testProduct.Name, fetchedProduct.Name); 

     Assert.AreNotEqual(Guid.Empty, createdProductObj.Id); 
     Assert.AreEqual(createdProductObj.Id, fetchedProduct.Id); 
    } 

一切工作正常，直到我嘗試插入具有多個相關實體的實體。讓我舉個例子。假設我有一個產品，它有一個FK ImageId，一個用於BrandId的FK和一個用於CategoryId的FK。 Brands實體已經爲Image實體提供了FK ImageId。

現在，當我嘗試插入新產品時，會插入2張圖片，一張來自品牌，另一張來自產品本身的圖片。所以在圖像表中，當我只需要一個新的產品圖像條目時，我會得到2個條目。此外，當我想要將現有圖像用於新產品時，這會造成問題。

所以我想創建一個新的服務/存儲庫的產品從通用服務/存儲庫繼承，並添加更多的邏輯。但是，有沒有更好的方法來做到這一點？

感謝您的幫助和時間

Answer 1

現在我明白了。

當使用客戶端進行測試時，mvc會使用json數據接收您的請求，並正確創建您的模型。

然而，MVC不知道你想的一樣Image的產品和品牌，它會爲每一個創建一個實例，就像這樣（我簡化，例如用途）：

var product = new Product(); 
var brand = new Brand(); 
product.Image = new Image(); 
product.Brand = brand; 
brand.Image = new Image(); // new image with same info... 

同樣，實體框架將假定它們是具有相同數據的兩個不同圖像。只要讓它知道這是一樣的，在你的行動做這樣的事情（當然你可以創建一個更好的代碼，這僅僅是一個快速樣品）：

[HttpPost] 
public IActionResult Create([FromBody] Product product) 
{ 
    if (product == null) 
     return BadRequest(); 

    // If the image already exists...nullify image so EF won't try to insert a new one... 
    if (product.ImageId > 0) 
     product.Image = null; 
    // If the image already exists...and the brand doesn't have an existing image, use the same image and nullify the brand's image as well... 
    if (product.ImageId > 0 && product.Brand != null && !(product.Brand.ImageId > 0)) 
    { 
     product.Brand.ImageId = product.ImageId; 
     product.Brand = null; 
    } 
    // If product is reveiving a new image...and the brand doesn't have an existing image, use the same new image... 
    if (product.Image != null && product.Brand != null && !(product.Brand.ImageId > 0)) 
     product.Brand.Image = product.Image; 

    var result = _productsService.Add(product, m => m.Name == product.Name); 
    if (result) 
    { 
     return CreatedAtRoute("GetProducts", new { id = product.Id }, product); 

    } 
    return BadRequest("Item not added"); 
} 

---

只需在控制檯測試應用程序如下所示轉載它。有些類：

public class Brand 
{ 
    public int Id { get; set; } 
    public virtual Image Image { get; set; } 
    public int ImageId { get; set; } 

} 

public class Image 
{ 
    public int Id { get; set; } 
} 

public class Product 
{ 
    public int Id { get; set; } 
    public virtual Image Image { get; set; } 
    public virtual Brand Brand { get; set; } 
    public int ImageId { get; set; } 
    public int BrandId { get; set; } 
} 

的DbContext與配置：

public class MyDbContext : DbContext 
{ 
    public DbSet<Product> Products { get; set; } 

    public DbSet<Brand> Brands { get; set; } 

    public DbSet<Image> Images { get; set; } 

    public MyDbContext() 
     : base("name=MyDbContext") 
    { 
    } 

    protected override void OnModelCreating(DbModelBuilder modelBuilder) 
    { 

     modelBuilder.Conventions.Remove<OneToManyCascadeDeleteConvention>(); 
     modelBuilder.Conventions.Remove<ManyToManyCascadeDeleteConvention>(); 
     modelBuilder.Conventions.Remove<PluralizingTableNameConvention>(); 

     modelBuilder.Properties<int>().Where(p => p.Name == "Id").Configure(p => p.IsKey()); 
     modelBuilder.Entity<Product>().HasRequired(p => p.Brand).WithMany().HasForeignKey(p => p.BrandId); 
     modelBuilder.Entity<Product>().HasRequired(p => p.Image).WithMany().HasForeignKey(p => p.ImageId); 
     modelBuilder.Entity<Brand>().HasRequired(p => p.Image).WithMany().HasForeignKey(p => p.ImageId); 

    } 
} 

於是最後，代碼本身。

我用的是同一個實例這第一種情況：

class Program 
{ 
    static void Main(string[] args) 
    { 

     using (var db = new MyDbContext()) 
     { 

      var image = new Image(); 
      var product = new Product(); 
      var brand = new Brand(); 
      product.Image = image; 
      product.Brand = brand; 
      brand.Image = image; // same instance 

      db.Products.Add(product); 

      db.SaveChanges(); 

     } 

    } 
} 

我的結果是：

然後我又跑了，現在用的是新的實例：

class Program 
{ 
    static void Main(string[] args) 
    { 

     using (var db = new MyDbContext()) 
     { 

      var image = new Image(); 
      var product = new Product(); 
      var brand = new Brand(); 
      product.Image = image; 
      product.Brand = brand; 
      brand.Image = new Image(); 

      db.Products.Add(product); 

      db.SaveChanges(); 

     } 

    } 
} 

現在我們有兩個新的圖像：

Answer 2

您必須保存圖像第一，然後保存引用它的實體。否則，實體框架將每個實例看作是應單獨保存的新實例。