我正在 ASP.NET Core 中开发一个管理系统项目，在将相关实体保存到数据库时遇到了问题。我将使用一个简化的示例来描述该问题。我有两个

我正在 ASP.NET Core 中开发一个管理系统项目，在将相关实体保存到数据库时遇到了问题。我将使用一个简化的示例来描述该问题。以下屏幕截图中有两个可见的类。我还有一个端点，它应该创建一个新的 Car 实例并将其添加到 User 类中的 Cars 集合中，然后将更改保存到数据库。但是，当我调用此端点时，出现以下异常：

Microsoft.EntityFrameworkCore.DbUpdateConcurrencyException：数据库操作预计会影响 1 行，但实际影响了 0 行；自加载实体以来数据可能已被修改或删除。

我查看了微软文档，似乎我的代码与示例没有什么不同，所以如果有人能解释问题出在哪里，我将不胜感激。

模型：

public class User : BaseEntity
{
    public string FirstName { get; protected set; }
    public string LastName { get; protected set; }
    public ICollection<Car> Cars { get; set; }
    
    
    public User(){}
    public User(Guid id, string firstName, string lastName)
    {
        Id = id;
        FirstName = firstName;
        LastName = lastName;
    }

    public void AddCar(Car car)
    {
        Cars.Add(car);
    }
}

public class Car : BaseEntity
{
    public string Model { get; protected set; }
    public DateOnly Year { get; protected set; }
    public Guid UserId { get;  set; }
    public User User { get;  protected set; }
    
    
    public Car() {}
    public Car(Guid id, string model, DateOnly year)
    {
        Id = id;
        Model = model;
        Year = year;
    }
}

语境：

public class AppDbContext : DbContext
{
    public AppDbContext() { }
    public AppDbContext(DbContextOptions<AppDbContext> options) : base(options) { }
    
    
    public DbSet<User> Users { get; set; }
    public DbSet<Car> Cars { get; set; }
    
    
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
        modelBuilder.HasDefaultSchema("test");

        modelBuilder.Entity<User>(entity =>
        {
            entity.HasKey(x => x.Id);

            entity.HasMany(u => u.Cars)
                .WithOne(c => c.User)
                .HasForeignKey(c => c.UserId);
        });
        
        modelBuilder.Entity<Car>(entity =>
        {
            entity.HasKey(c => c.Id);

            entity.HasOne(c => c.User)
                .WithMany(u => u.Cars)
                .HasForeignKey(c => c.UserId);
        });
        
        modelBuilder.ApplyConfigurationsFromAssembly(Assembly.GetExecutingAssembly());
    }
}

端点：

[HttpPost("{userId}/add-car")]
    public async Task<IActionResult> AddCar(Guid userId, [FromBody] AddCarRequest request)
    {
        await using (var context = new AppDbContext())
        {
            var car = new Car(Guid.NewGuid(), request.Model, request.Year);
            var user =  context.Users.Include(x => x.Cars).FirstOrDefault(x => x.Id == userId);
            

            user.AddCar(car);
            
            await context.SaveChangesAsync();

            return Ok();
        }
    }

例外：

Microsoft.EntityFrameworkCore.DbUpdateConcurrencyException: The database operation was expected to affect 1 row(s), but actually affected 0 row(s); data may have been modified or deleted since entities were loaded. See https://go.microsoft.com/fwlink/?LinkId=527962 for information on understanding and handling optimistic concurrency exceptions.
   at Npgsql.EntityFrameworkCore.PostgreSQL.Update.Internal.NpgsqlModificationCommandBatch.ThrowAggregateUpdateConcurrencyExceptionAsync(RelationalDataReader reader, Int32 commandIndex, Int32 expectedRowsAffected, Int32 rowsAffected, CancellationToken cancellationToken)
   at Npgsql.EntityFrameworkCore.PostgreSQL.Update.Internal.NpgsqlModificationCommandBatch.Consume(RelationalDataReader reader, Boolean async, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Update.ReaderModificationCommandBatch.ExecuteAsync(IRelationalConnection connection, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Update.ReaderModificationCommandBatch.ExecuteAsync(IRelationalConnection connection, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.ExecuteAsync(IEnumerable`1 commandBatches, IRelationalConnection connection, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.ExecuteAsync(IEnumerable`1 commandBatches, IRelationalConnection connection, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.ExecuteAsync(IEnumerable`1 commandBatches, IRelationalConnection connection, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChangesAsync(IList`1 entriesToSave, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChangesAsync(StateManager stateManager, Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken)
   at Npgsql.EntityFrameworkCore.PostgreSQL.Storage.Internal.NpgsqlExecutionStrategy.ExecuteAsync[TState,TResult](TState state, Func`4 operation, Func`4 verifySucceeded, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.DbContext.SaveChangesAsync(Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken)
   at EFTest.Controllers.DefaultController.AddCar(Guid userId, AddCarRequest request) in S:\Repos\EFTest\EFTest\Controllers\DefaultController.cs:line 38
   at EFTest.Controllers.DefaultController.AddCar(Guid userId, AddCarRequest request) in S:\Repos\EFTest\EFTest\Controllers\DefaultController.cs:line 40
   at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.TaskOfIActionResultExecutor.Execute(ActionContext actionContext, 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|20_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.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Logged|17_1(ResourceInvoker invoker)
   at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
   at Swashbuckle.AspNetCore.SwaggerUI.SwaggerUIMiddleware.Invoke(HttpContext httpContext)
   at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext, ISwaggerProvider swaggerProvider)
   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)

我将我的代码与微软的文档进行了比较，在我看来，一切似乎都是正确的。

using (var context = new BloggingContext())
{
    var blog = context.Blogs.Include(b => b.Posts).First();
    var post = new Post { Title = "Intro to EF Core" };

    blog.Posts.Add(post);
    context.SaveChanges();
}

EF 执行的查询：

info: 13.09.2024 20:51:02.616 RelationalEventId.CommandExecuted[20101] (Microsoft.EntityFrameworkCore.Database.Command) 
      Executed DbCommand (20ms) [Parameters=[@__userId_0='42d2ac6e-e663-41a9-830e-3e49b38634c9'], CommandType='Text', CommandTimeout='30']
      SELECT t."Id", t."CreatedAt", t."FirstName", t."LastName", t."UpdatedAt", c."Id", c."CreatedAt", c."Model", c."UpdatedAt", c."UserId", c."Year"
      FROM (
          SELECT u."Id", u."CreatedAt", u."FirstName", u."LastName", u."UpdatedAt"
          FROM test."Users" AS u
          WHERE u."Id" = @__userId_0
          LIMIT 1
      ) AS t
      LEFT JOIN test."Cars" AS c ON t."Id" = c."UserId"
      ORDER BY t."Id"
info: 13.09.2024 20:51:03.025 RelationalEventId.CommandExecuted[20101] (Microsoft.EntityFrameworkCore.Database.Command) 
      Executed DbCommand (23ms) [Parameters=[@p5='7c87ad78-534b-4e1c-a472-653eab8a0fb9', @p0='0001-01-01T00:00:00.0000000' (DbType = DateTime), @p1='TEST' (Nullable = false), @p2='0001-01-01T00:00:00.0000000' (DbType = DateTime), @p3='42d2ac6e-e663-41a9-830e-3e49b38634c9', @p4='01/01/2000' (DbType = Date)], CommandType='Text', CommandTimeout='30']
      UPDATE test."Cars" SET "CreatedAt" = @p0, "Model" = @p1, "UpdatedAt" = @p2, "UserId" = @p3, "Year" = @p4
      WHERE "Id" = @p5;