EF: an instance of an object of type X cannot be traced because another instance of this type with the same key is already traced

Question

I send the user object in Json format in my HTTP request as follows:

POST http://localhost:52054/api/Authentication/DeleteAccessToken HTTP/1.1
Host: localhost:52054
Content-Type: application/json

{"id":1,"userName":"mnoureldin","accessToken":{"id":1,"token":"123ABC456EFG","userId":1}}

And my controller (in EF-core ) handles the following:

[HttpPost]
public IActionResult DeleteAccessToken([FromBody]User user)
{
    using (var Context = new UnitOfWork().Context)
    {
        var userEntity = Context.Users.Find(user.Id); // Get the real entity of the user received as json
        if (userEntity != null)
        {
            var accessTokenEntity = Context.AccessTokens.Find(userEntity.AccessToken.Id); // Find the entity of the accesstoken (I tried also directly by accessing the navigation property of user entity)
            Context.AccessTokens.Remove(accessTokenEntity);
            return Ok();
        }
        else
        {
            return Unauthorized();
        }
    }
}

But the line Context.AccessTokens.Remove(accessTokenEntity);throws this exception:

An exception of type "System.InvalidOperationException" occurred in Microsoft.EntityFrameworkCore.dll, but was not processed in the user code

: "AccessToken" , . , , (.. ). , , . , .

AccessToken userEntity .

UnitOfWork:

public UnitOfWork()
{
    // Configure EF connection
    var optionsBuilder = new DbContextOptionsBuilder<CustomDbContext>();
    optionsBuilder
        .UseMySQL(@"server=192.168.1.35; port=3306; sslmode=none;
                    userid=root;
                    pwd=P@ssword;
                    database=dotnet;");

    Context = new CustomDbContext(optionsBuilder.Options);

    // Configure data loading method to explicit
    Context.AccessTokens.Load();
}

My CustomBdContext:

public class CustomDbContext : DbContext
{
    // Tell EF to map the entities to tables
    public DbSet<User> Users { get; set; }
    public DbSet<AccessToken> AccessTokens { get; set; }

    public CustomDbContext(DbContextOptions options) : base(options)
    {
    }
}

:

User ----- AccessToken

:

public class User
{
    public int Id { get; set; }
    public string UserName { get; set; }

    public virtual AccessToken AccessToken { get; set; }
}

:

public class AccessToken
{
    public int Id { get; set; }
    public string Token { get; set; }

    [ForeignKey("User"), Required]
    public int UserId { get; set; }
    public virtual User User { get; set; }
}

- ? , .

Answer 1

, EF user AccessToken . , .

Try

[HttpPost]
public IActionResult DeleteAccessToken([FromBody]User user)
{
    // Requires System.Linq
    if (Context.Users.Any(u => u.Id == user.Id))
    {
        var accessTokenEntity = Context.AccessTokens.Find(user.AccessToken.Id); // Find the entity of the accesstoken (I tried also directly by accessing the navigation property of user entity)
        Context.AccessTokens.Remove(accessTokenEntity);

        // NOTE: You re not saving?
        return Ok();
    }
    else
    {
        return Unauthorized();
    }
}

:

[HttpPost]
public IActionResult DeleteAccessToken([FromBody]User user)
{
    if (Context.Users.Any(u => u.Id == user.Id))
    {
        Context.AccessTokens.Remove(user.AccessToken);
        return Ok();
    }
    else
    {
        return Unauthorized();
    }
}

Answer 2

:

var accessTokenEntity = Context.AccessTokens.Find(userEntity.AccessToken.Id);

var accessTokenEntity = Context.AccessTokens.AsNoTracking().Find(userEntity.AccessToken.Id);