Cannot be tracked because another instance of this type with the same key is already being tracked

When i’m trying to add continous same entity with difference key i has an error.

var trans = _context.Database.BeginTransaction();
            NhomNguoiDung nnd = new NhomNguoiDung()
            {
                NhomNguoiDung_Ma = Guid.NewGuid(),
                NhomNguoiDung_Ten = "Administrators"
            };
            _context.Add(nnd);

            NguoiDung nd = new NguoiDung()
            {
                NguoiDung_Ma = Guid.NewGuid(),
                NguoiDung_TaiKhoan = "Administrator",
                NguoiDung_MatKhau = "-----+++-----"
            };
            _context.Add(nd);

            PhanNhomNguoiDung pnnd = new PhanNhomNguoiDung()
            {
                PhanNhomNguoiDung_NguoiDung = nd.NguoiDung_Ma,
                PhanNhomNguoiDung_NhomNguoiDung = nnd.NhomNguoiDung_Ma
            };
            _context.Add(pnnd);
            foreach(var t  in Roles.ListOfRole()) // List of role about 24 role with difference name
            {
                var qh = new QuyenHan()
                {
                    QuyenHan_Ma = Guid.NewGuid(),
                    QuyenHan_Ten = t
                };
                _context.Add(qh); // 2nd item add OK

                var pqnnd = new PhanQuyenNhomNguoiDung() // PhanQuyenNhomNguoiDung_NhomNguoiDung & PhanQuyenNhomNguoiDung_QuyenHan  Is Primarykey
                {
                    PhanQuyenNhomNguoiDung_NhomNguoiDung = nnd.NhomNguoiDung_Ma,
                    PhanQuyenNhomNguoiDung_QuyenHan = qh.QuyenHan_Ma // new Key but error for what ???
                };
               // 2nd item add has ERROR
                _context.PhanQuyenNhomNguoiDung.Add(pqnnd);
            };`

Stack Trace

An unhandled exception occurred while processing the request.

InvalidOperationException: The instance of entity type ‘PhanQuyenNhomNguoiDung’ cannot be tracked because another instance of this type with the same key is already being tracked. When adding new entities, for most key types a unique temporary key value will be created if no key is set (i.e. if the key property is assigned the default value for its type). If you are explicitly setting key values for new entities, ensure they do not collide with existing entities or temporary values generated for other new entities. When attaching existing entities, ensure that only one entity instance with a given key value is attached to the context. Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IdentityMap.Add(TKey key, InternalEntityEntry entry)

Stack Query Cookies Headers InvalidOperationException: The instance of entity type ‘PhanQuyenNhomNguoiDung’ cannot be tracked because another instance of this type with the same key is already being tracked. When adding new entities, for most key types a unique temporary key value will be created if no key is set (i.e. if the key property is assigned the default value for its type). If you are explicitly setting key values for new entities, ensure they do not collide with existing entities or temporary values generated for other new entities. When attaching existing entities, ensure that only one entity instance with a given key value is attached to the context. Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IdentityMap.Add(TKey key, InternalEntityEntry entry) Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IdentityMap.Add(InternalEntityEntry entry) Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.StartTracking(InternalEntityEntry entry) Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntry.SetEntityState(EntityState oldState, EntityState newState, bool acceptChanges) Microsoft.EntityFrameworkCore.ChangeTracking.Internal.EntityGraphAttacher.PaintAction(EntityEntryGraphNode node) Microsoft.EntityFrameworkCore.ChangeTracking.Internal.EntityEntryGraphIterator.TraverseGraph(EntityEntryGraphNode node, Func<EntityEntryGraphNode, bool> handleNode) Microsoft.EntityFrameworkCore.DbContext.SetEntityState<TEntity>(TEntity entity, EntityState entityState) QuanLyDoanVien.Controllers.SetupController.InitData() in SetupController.cs + _context.PhanQuyenNhomNguoiDung.Add(pqnnd); QuanLyDoanVien.Controllers.SetupController.InitData(string key) in SetupController.cs + InitData(); lambda_method(Closure , object , Object[] ) Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker+<InvokeActionMethodAsync>d__27.MoveNext() System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker+<InvokeNextActionFilterAsync>d__25.MoveNext() Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.Rethrow(ActionExecutedContext context) Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.Next(ref State next, ref Scope scope, ref object state, ref bool isCompleted) Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker+<InvokeNextResourceFilter>d__22.MoveNext() Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.Rethrow(ResourceExecutedContext context) Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.Next(ref State next, ref Scope scope, ref object state, ref bool isCompleted) Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker+<InvokeAsync>d__20.MoveNext() System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) Microsoft.AspNetCore.Builder.RouterMiddleware+<Invoke>d__4.MoveNext() System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) Microsoft.AspNetCore.Authentication.AuthenticationMiddleware+<Invoke>d__18.MoveNext() Microsoft.AspNetCore.Authentication.AuthenticationMiddleware+<Invoke>d__18.MoveNext() System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) Microsoft.AspNetCore.Session.SessionMiddleware+<Invoke>d__9.MoveNext() Microsoft.AspNetCore.Session.SessionMiddleware+<Invoke>d__9.MoveNext() System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) Microsoft.VisualStudio.Web.BrowserLink.Runtime.BrowserLinkMiddleware+<ExecuteWithFilter>d__7.MoveNext() System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore.MigrationsEndPointMiddleware+<Invoke>d__5.MoveNext() System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore.DatabaseErrorPageMiddleware+<Invoke>d__6.MoveNext() Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore.DatabaseErrorPageMiddleware+<Invoke>d__6.MoveNext() System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware+<Invoke>d__7.MoveNext()

Show raw exception details

Raw exception details:

System.InvalidOperationException: The instance of entity type 'PhanQuyenNhomNguoiDung' cannot be tracked because another instance of this type with the same key is already being tracked. When adding new entities, for most key types a unique temporary key value will be created if no key is set (i.e. if the key property is assigned the default value for its type). If you are explicitly setting key values for new entities, ensure they do not collide with existing entities or temporary values generated for other new entities. When attaching existing entities, ensure that only one entity instance with a given key value is attached to the context.
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IdentityMap`1.Add(TKey key, InternalEntityEntry entry)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IdentityMap`1.Add(InternalEntityEntry entry)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.StartTracking(InternalEntityEntry entry)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntry.SetEntityState(EntityState oldState, EntityState newState, Boolean acceptChanges)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.EntityGraphAttacher.PaintAction(EntityEntryGraphNode node)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.EntityEntryGraphIterator.TraverseGraph(EntityEntryGraphNode node, Func`2 handleNode)
   at Microsoft.EntityFrameworkCore.DbContext.SetEntityState[TEntity](TEntity entity, EntityState entityState)
   at QuanLyDoanVien.Controllers.SetupController.InitData() in T:\Projects\QuanLyDoanVien\src\QuanLyDoanVien\Controllers\SetupController.cs:line 134
   at QuanLyDoanVien.Controllers.SetupController.InitData(String key) in T:\Projects\QuanLyDoanVien\src\QuanLyDoanVien\Controllers\SetupController.cs:line 43
   at lambda_method(Closure , Object , Object[] )
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeActionMethodAsync>d__27.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeNextActionFilterAsync>d__25.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.Rethrow(ActionExecutedContext context)
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeNextResourceFilter>d__22.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.Rethrow(ResourceExecutedContext context)
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeAsync>d__20.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNetCore.Builder.RouterMiddleware.<Invoke>d__4.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware`1.<Invoke>d__18.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware`1.<Invoke>d__18.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNetCore.Session.SessionMiddleware.<Invoke>d__9.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Session.SessionMiddleware.<Invoke>d__9.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.VisualStudio.Web.BrowserLink.Runtime.BrowserLinkMiddleware.<ExecuteWithFilter>d__7.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore.MigrationsEndPointMiddleware.<Invoke>d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore.DatabaseErrorPageMiddleware.<Invoke>d__6.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore.DatabaseErrorPageMiddleware.<Invoke>d__6.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.<Invoke>d__7.MoveNext()

project.json file:

"dependencies": {
    "Microsoft.AspNetCore.Authentication.Cookies": "1.1.0",
    "Microsoft.AspNetCore.Diagnostics": "1.1.0",
    "Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore": "1.1.0",
    "Microsoft.AspNetCore.Identity.EntityFrameworkCore": "1.1.0",
    "Microsoft.AspNetCore.Mvc": "1.1.0",
    "Microsoft.AspNetCore.Mvc.Razor": "1.1.0",
    "Microsoft.AspNetCore.Razor.Tools": {
      "version": "1.1.0-preview4-final",
      "type": "build"
    },
    "Microsoft.AspNetCore.Routing": "1.1.0",
    "Microsoft.AspNetCore.Server.IISIntegration": "1.1.0",
    "Microsoft.AspNetCore.Server.Kestrel": "1.1.0",
    "Microsoft.AspNetCore.Session": "1.1.0",
    "Microsoft.AspNetCore.StaticFiles": "1.1.0",
    "Microsoft.EntityFrameworkCore.SqlServer": "1.1.0",
    "Microsoft.EntityFrameworkCore.SqlServer.Design": {
      "version": "1.1.0",
      "type": "build"
    },
    "Microsoft.EntityFrameworkCore.Tools": {
      "version": "1.1.0-preview4-final",
      "type": "build"
    },
    "Microsoft.Extensions.Configuration.EnvironmentVariables": "1.1.0",
    "Microsoft.Extensions.Configuration.Json": "1.1.0",
    "Microsoft.Extensions.Configuration.UserSecrets": "1.1.0",
    "Microsoft.Extensions.Logging": "1.1.0",
    "Microsoft.Extensions.Logging.Console": "1.1.0",
    "Microsoft.Extensions.Logging.Debug": "1.1.0",
    "Microsoft.Extensions.Options.ConfigurationExtensions": "1.1.0",
    "Microsoft.Framework.Caching.Memory": "1.0.0-beta8",
    "Microsoft.VisualStudio.Web.BrowserLink.Loader": "14.1.0",
    "Microsoft.VisualStudio.Web.CodeGeneration.Tools": {
      "version": "1.1.0-preview4-final",
      "type": "build"
    },
    "Microsoft.VisualStudio.Web.CodeGenerators.Mvc": {
      "version": "1.1.0-preview4-final",
      "type": "build"
    }
  },

With Entity Core 1.0 work, but after update to 1.1.0 has this error

[nimeshvaghasiya]

@rickco75 I had same issue and get rid of it by below: In your case it will be: var record2 = _context.Contracts.AsNoTracking().Where(t => t.Id== id).FirstOrDefault();

AsNoTracking() may help you.

[smitpatel]

@rickco75 - When you query the database for record2 without using AsNoTracking EF will start tracking it in current context. So when you update contract in your code, EF finds multiple entities with same id hence the error. AsNoTracking is one solution as you are querying record2 just to find out the existence of entity and you don’t want EF to track any modifications to that (since you are not modifying it). In many cases not having AsNoTracking is fine as long as you don’t add/attach/update entity with same id in the context. But it is good to have it explicitly when tracking is not required.

Also, if you are just checking for existence then a query with count would be much better option. something like this _context.Contracts.Where(c => c.Id == id).Count() The benefits are

• It does not materialize the entity record2 hence query does not need to pull all the columns from database. Instead a normal Count would be put in Select part of SQL. Smaller query. Also it will fetch just a number as a data from server instead of all the column values.
• There is also extra cost of materializing objects which would be avoided.
• No need to worry about tracking since we are not creating entity objects.