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c# - 添加到实体中的集合

问题描述

我有一所班级学校，可以举办许多活动...

public class School: Entity<Guid>
{
    public string Name { get; set; }
    public ICollection<Event> Events { get; set; } = new List<Event>();
    public void AddEvent(Event newEvent) 
    {
        Events.Add(newEvent);
    }
}

这是事件类

public class Event : Entity<Guid>
{
    public string Title { get; set; }
    public string Description { get; set; }
    public DateTime EventStart { get; set; }
}

这是一个实体类 - 不相关，但如果有人想看

public abstract class Entity<TId> 
{
    public TId Id { get; set; }
}

当我想为学校添加一个新事件时，我使用事件类的属性调用一个 POST 端点。

[HttpPost]
public async Task<IActionResult> CreateEvent(Guid schoolId, Event newEvent)
{
     var school = await _context.School.FirstOrDefaultAsync(x => x.Id == schoolId);
     
     school.AddEvent(newEvent);
     
     await _context.SaveChangesAsync();
     
     return Ok();
}

但是，由于某种原因，这会导致此错误...

完整的堆栈跟踪：

System.ArgumentNullException: Value cannot be null. (Parameter 'key')
   at System.Collections.Generic.Dictionary`2.FindEntry(TKey key)
   at System.Collections.Generic.Dictionary`2.TryGetValue(TKey key, TValue& value)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.EntityReferenceMap.TryGet(Object entity, IEntityType entityType, InternalEntityEntry& entry, Boolean throwOnNonUniqueness)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.TryGetEntry(Object entity, IEntityType entityType, Boolean throwOnTypeMismatch)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.NavigationFixer.InitialFixup(InternalEntityEntry entry, Boolean fromQuery)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.NavigationFixer.StateChanged(InternalEntityEntry entry, EntityState oldState, Boolean fromQuery)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntryNotifier.StateChanged(InternalEntityEntry entry, EntityState oldState, Boolean fromQuery)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntry.FireStateChanged(EntityState oldState)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntry.SetEntityState(EntityState oldState, EntityState newState, Boolean acceptChanges, Boolean modifyProperties)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntry.SetEntityState(EntityState entityState, Boolean acceptChanges, Boolean modifyProperties, Nullable`1 forceStateWhenUnknownKey)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.EntityGraphAttacher.PaintAction(EntityEntryGraphNode`1 node)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.EntityEntryGraphIterator.TraverseGraph[TState](EntityEntryGraphNode`1 node, Func`2 handleNode)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.EntityEntryGraphIterator.TraverseGraph[TState](EntityEntryGraphNode`1 node, Func`2 handleNode)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.EntityEntryGraphIterator.TraverseGraph[TState](EntityEntryGraphNode`1 node, Func`2 handleNode)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.EntityGraphAttacher.AttachGraph(InternalEntityEntry rootEntry, EntityState targetState, EntityState storeGeneratedWithKeySetTargetState, Boolean forceStateWhenUnknownKey)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.NavigationFixer.NavigationCollectionChanged(InternalEntityEntry entry, INavigationBase navigationBase, IEnumerable`1 added, IEnumerable`1 removed)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntryNotifier.NavigationCollectionChanged(InternalEntityEntry entry, INavigationBase navigationBase, IEnumerable`1 added, IEnumerable`1 removed)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.ChangeDetector.DetectNavigationChange(InternalEntityEntry entry, INavigationBase navigationBase)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.ChangeDetector.LocalDetectChanges(InternalEntityEntry entry)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.ChangeDetector.DetectChanges(IStateManager stateManager)
   at Microsoft.EntityFrameworkCore.ChangeTracking.ChangeTracker.DetectChanges()
   at Microsoft.EntityFrameworkCore.DbContext.TryDetectChanges()
   at Microsoft.EntityFrameworkCore.DbContext.SaveChangesAsync(Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken)
   at MakersOfDenmark.WebAPI.Controllers.EventController.CreateEvent(Guid schoolId, Event newEvent) in C:\Users\mathi\Source\Repos\makersofdenmark\src\MakersOfDenmark.WebAPI\Controllers\EventController.cs:line 50
   at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.TaskOfIActionResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Logged|12_1(ControllerActionInvoker invoker)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterAsync>g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeInnerFilterAsync>g__Awaited|13_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|19_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Logged|17_1(ResourceInvoker invoker)
   at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
   at Swashbuckle.AspNetCore.SwaggerUI.SwaggerUIMiddleware.Invoke(HttpContext httpContext)
   at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext, ISwaggerProvider swaggerProvider)
   at Serilog.AspNetCore.RequestLoggingMiddleware.Invoke(HttpContext httpContext)
   at Elmah.Io.AspNetCore.Serilog.ElmahIoSerilogMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)

提前致谢。

标签： c#entity-framework-core

解决方案

尝试添加学校和事件之间的关系。

public class School: Entity<Guid>
{
    public string Name { get; set; }
    public ICollection<Event> Events { get; set; } = new List<Event>();

    public void AddEvent(Event newEvent) 
    {
        Events.Add(newEvent);
    }
}

public class Event : Entity<Guid>
{
    public string Title { get; set; }
    public string Description { get; set; }
    public DateTime EventStart { get; set; }
    public School School { get;set; }
    public Guid SchoolId { get;set; }
}


//on your DB context
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Event>().HasOne(x => x.School).WithMany(x => x.Events);
}

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