我正在添加一个实体类别作为另一个实体产品的属性 System.ArgumentException：已添加具有相同键的项目

如何解决我正在添加一个实体类别作为另一个实体产品的属性 System.ArgumentException：已添加具有相同键的项目

在我的 API 项目中，有实体 Category 如下：

    [Key]
    public string Id { get; set; }                
    public string Title { get; set; }
    public Category(string id,string title)
    
    

以及类别是属性的实体产品：

    [Key]
    public string Id { get; set; }

    [required(ErrorMessage = "Título é obrigatório.")]
    [MaxLength(60,ErrorMessage = "Este campo deve conter enre 3 e 60 caracteres.")]
    [MinLength(3,ErrorMessage = "Este campo deve conter enre 3 e 60 caracteres.")]
    public string Title { get; set; }

    [MaxLength(1024,ErrorMessage = "Este campo deve ter no máximo 1024 caracteres")]
    public string Description { get; set; }

    [required(ErrorMessage = "Este campo é obrigatório")]
    [Range(1,int.MaxValue,ErrorMessage = "O preço deve ser maior que zero")]
    public decimal Price { get; set; }
    public int AvailableQuantity { get; set; }

    [required(ErrorMessage = "Este campo é obrigatório")]
    public string CategoryId { get; set; }

    public Category Category { get; set; }

这是 ProductController 中的 Create 方法：

    [HttpPost]
    [AllowAnonymous]
    public async Task<ActionResult<Product>> Create([FromBody] Product model)
    {
        var category = _context.Categories.AsNoTracking().FirstOrDefault(x => x.Id == model.CategoryId);

        if (category == null)
            return Ok("Categoria informada não existe");


        if (ModelState.IsValid)
        {
            _product.GenerateId(model);
            var product = new Product(model.Id,model.Title,model.Description,model.Price,model.CategoryId,category);
            _context.Products.Add(product);
            await _context.SaveChangesAsync();
            return product;
        }
        else
        {
            return BadRequest(ModelState);
        }
    }

当我尝试创建一个新产品时，我收到如下错误消息：

System.ArgumentException：已添加具有相同键的项目。钥匙：280CF21D 在 System.Collections.Generic.Dictionary2.TryInsert(TKey key,TValue value,InsertionBehavior behavior) at System.Collections.Generic.Dictionary2.Add(TKey key,TValue value) 在 Microsoft.EntityFrameworkCore.InMemory.Storage.Internal.InMemoryTable1.Create(IUpdateEntry entry) at Microsoft.EntityFrameworkCore.InMemory.Storage.Internal.InMemoryStore.ExecuteTransaction(IList1 个条目，IDiagnosticslogger1 updateLogger) at Microsoft.EntityFrameworkCore.InMemory.Storage.Internal.InMemoryDatabase.SaveChangesAsync(IList1 个条目，CancellationToken 取消令牌） 在 Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChangesAsync(IList1 entriesToSave,CancellationToken cancellationToken) at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChangesAsync(DbContext _,Boolean acceptAllChangesOnSuccess,CancellationToken cancellationToken) at Microsoft.EntityFrameworkCore.DbContext.SaveChangesAsync(Boolean acceptAllChangesOnSuccess,CancellationToken cancellationToken) at TesteAPI.Controllers.ProductsController.Create(Product model) in C:\Users\tcho3\source\repos\TesteAPI\TesteAPI\Controllers\ProductsController.cs:line 93 at lambda_method56(Closure,Object ) at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.AwaitableObjectResultExecutor.Execute(IActionResultTypeMapper mapper,ObjectMethodExecutor executor,Object controller,Object[] arguments) at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Awaited|12_0(ControllerActionInvoker invoker,ValueTask1 actionResultValueTask) 在 Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.g__Awaited|10_0（ControllerActionInvoker 调用者，任务上一个任务，下一个状态，作用域范围，对象状态，布尔值已完成） 在 Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context) 在 Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next,Scope& scope,Object& state,Boolean& isCompleted) 在 Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeInnerFilterasync() --- 从上一个位置开始的堆栈跟踪结束 --- 在 Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g__Awaited|19_0(ResourceInvoker invoker,Task lastTask,State next,Scope scope,Object state,Boolean isCompleted) 在 Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g__Awaited|17_0（ResourceInvoker 调用者，任务任务，Idisposable 范围） 在 Microsoft.AspNetCore.Routing.EndpointMiddleware.g__AwaitRequestTask|6_0(Endpoint endpoint,Task requestTask,ILogger logger) 在 Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext 上下文) 在 Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext 上下文) 在 Swashbuckle.AspNetCore.SwaggerUI.SwaggerUIMiddleware.Invoke(HttpContext httpContext) 在 Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext,ISwaggerProvider swaggerProvider) 在 Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)

解决方法

修复模型

public class Category 
{
    [Key]
    public string Id { get; set; }                
    public string Title { get; set; }
    .....

   public virtual ICollection<Product> Products { get; set}
}

您也不需要 Product 的特殊构造函数，因为您使用 Product 作为模型

修正你的行为

  public async Task<ActionResult<Product>> Create([FromBody] Product model)
    {
     
//---------- I don't think that you really need this

  var category = _context.Categories.AsNoTracking().FirstOrDefault(x => x.Id == model.CategoryId);
        if (category == null)  return Ok("Categoria informada não existe");

//---------

 //would be enough
    if (model.category == 0)  return Ok("Categoria informada não existe");



        if (ModelState.IsValid)
        {
            _product.GenerateId(model);
            _context.Products.Add(model;
            await _context.SaveChangesAsync();
            return model;
        }
        else
        {
            .....
        }
    }

,

是的，因为该类别已存在于数据库中，因此与该产品相关的类别您只需在创建产品时传递 CategoryId，如下所示：

var product = new Product(model.Id,model.Title,model.Description,model.Price,model.CategoryId);

无需传递 category 对象。