entity object cannot be referenced by multiple instances of IEntityChangeTracker while adding related objects to entity in Entity Framework 4 1

Question

I am trying to save Employee details  which has references with City  But everytime I try to save my contact  which is validated I get the exception  ADO Net Entity Framework An entity object cannot be referenced by multiple instances of IEntityChangeTracker   I had read so many post but still not getting the exact idea of what to do    my Save button click code is given below  protected void Button1 Click object sender  EventArgs e                EmployeeService es   new EmployeeService            CityService cs   new CityService             DateTime dt   new DateTime 2008  12  12           Payroll Entities Employee e1   new Payroll Entities Employee             Payroll Entities City city1   cs SelectCity Convert ToInt64 cmbCity SelectedItem Value             e1 Name    Archana           e1 Title    aaaa           e1 BirthDate   dt          e1 Gender    F           e1 HireDate   dt          e1 MaritalStatus    M           e1 City   city1                   es AddEmpoyee e1 city1           and Employeeservice Code  public string AddEmpoyee Payroll Entities Employee e1  Payroll Entities City c1                        Payroll DAO1 payrollDAO   new Payroll DAO1                payrollDAO AddToEmployee e1      Here I am getting Error               payrollDAO SaveChanges                return  SUCCESS

User · Answer

This is an old thread  but another solution  which I prefer  is just update the cityId and not assign the hole model City to Employee    to do that Employee should look like   public class Employee              public int  CityId    The   is for allow City nullable     public virtual City City      Then it s enough assigning   e1 CityId city1 ID

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Steps to reproduce can be simplified to this   var contextOne   new EntityContext    var contextTwo   new EntityContext     var user   contextOne Users FirstOrDefault     var group   new Group    group User   user   contextTwo Groups Add group   contextTwo SaveChanges      Code without error   var context   new EntityContext     var user   context Users FirstOrDefault     var group   new Group    group User   user     Be careful when you set entity properties      Be sure that all objects came from the same context  context Groups Add group   context SaveChanges      Using only one EntityContext can solve this  Refer to other answers for other solutions

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Error source   ApplicationUser user   await UserManager FindByIdAsync User Identity Name   ApplicationDbContext db   new ApplicationDbContent    db Users Uploads Add new MyUpload FileName  newfile png     await db SavechangesAsync    ZZZZZZZ   Hope someone saves some precious time

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I had the same problem but my issue with the  Slauma s solution  although great in certain instances  is that it recommends that I pass the context into the service which implies that the context is available from my controller   It also forces tight coupling between my controller and service layers     I m using Dependency Injection to inject the service repository layers into the controller and as such do not have access to the context from the controller     My solution was to have the service repository layers use the same instance of the context - Singleton     Context Singleton Class     Reference  http   msdn microsoft com en-us library ff650316 aspx and http   csharpindepth com Articles General Singleton aspx  public sealed class MyModelDbContextSingleton     private static readonly MyModelDbContext instance   new MyModelDbContext       static MyModelDbContextSingleton          private MyModelDbContextSingleton          public static MyModelDbContext Instance         get             return instance                  Repository Class   public class ProjectRepository   IProjectRepository     MyModelDbContext context   MyModelDbContextSingleton Instance            Other solutions do exist such as instantiating the context once and passing it into the constructors of your service repository layers or another I read about which is implementing the Unit of Work pattern   I m sure there are more

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Use the same DBContext object throughout the transaction

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This is how I encountered this issue  First I need to save my Order which needs a reference to my ApplicationUser table     ApplicationUser user   new ApplicationUser      user   UserManager FindById User Identity GetUserId        Order entOrder   new Order      entOrder ApplicationUser   user    I need this user before saving to my database using EF   The problem is that I am initializing a new ApplicationDbContext to save my new Order entity    ApplicationDbContext db   new ApplicationDbContext     db Entry entOrder  State   EntityState Added   db SaveChanges      So in order to solve the problem  I used the same ApplicationDbContext instead of using the built-in UserManager of ASP NET MVC   Instead of this   user   UserManager FindById User Identity GetUserId       I used my existing ApplicationDbContext instance     db instance here is the same instance as my db on my code above  user   db Users Find User Identity GetUserId

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Because these two lines      EmployeeService es   new EmployeeService    CityService cs   new CityService          don t take a parameter in the constructor  I guess that you create a context within the classes  When you load the city1     Payroll Entities City city1   cs SelectCity            you attach the city1 to the context in CityService  Later you add a city1 as a reference to the new Employee e1 and add e1 including this reference to city1 to the context in EmployeeService  As a result you have city1 attached to two different context which is what the exception complains about   You can fix this by creating a context outside of the service classes and injecting and using it in both services   EmployeeService es   new EmployeeService context   CityService cs   new CityService context      same context instance   Your service classes look a bit like repositories which are responsible for only a single entity type  In such a case you will always have trouble as soon as relationships between entities are involved when you use separate contexts for the services   You can also create a single service which is responsible for a set of closely related entities  like an EmployeeCityService  which has a single context  and delegate the whole operation in your Button1 Click method to a method of this service

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I hit this same problem after implementing IoC for a project  ASP Net MVC EF6 2    Usually I would initialise a data context in the constructor of a controller and use the same context to initialise all my repositories   However using IoC to instantiate the repositories caused them all to have separate contexts and I started getting this error   For now I ve gone back to just newing up the repositories with a common context while I think of a better way

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In this case  it turns out the error is very clear  Entity Framework cannot track an entity using multiple instances of IEntityChangeTracker or typically  multiple instances of DbContext  The solutions are  use one instance of DbContext  access all needed entities through a single repository  depending on one instance of DbContext   or turning off tracking for all entities accessed via a repository other than the one throwing this particular exception   When following an inversion of control pattern in  Net Core Web API  I frequently find that I have controllers with dependencies such as   private readonly IMyEntityRepository myEntityRepo     depends on MyDbContext private readonly IFooRepository fooRepo     depends on MyDbContext private readonly IBarRepository barRepo     depends on MyDbContext public MyController      IMyEntityRepository myEntityRepo       IFooRepository fooRepo       IBarRepository barRepo        this fooRepo   fooRepo      this barRepo   barRepo      this myEntityRepo   myEntityRepo      and usage like      myEntity Foo   await this fooRepository GetFoos   SingleOrDefaultAsync f   gt  f Id    model FooId   if  model BarId HasValue        myEntity Foo Bar   await this barRepository GetBars   SingleOrDefaultAsync b   gt  b Id    model BarId Value          await this myEntityRepo UpdateAsync myEntity      this throws an error    Since all three repositories depend on different DbContext instances per request  I have two options to avoid the problem and maintain separate repositories  change the injection of the DbContext to create a new instance only once per call      services AddTransient lt DbContext  MyDbContext gt      lt - one instance per ctor  bad services AddScoped lt DbContext  MyDbContext gt         lt - one instance per call  good    or  if the child entity is being used in a read-only manner  turning off tracking on that instance   myEntity Foo Bar   await this barRepo GetBars   AsNoTracking   SingleOrDefault b   gt  b Id    model BarId

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I had the same problem and I could solve making a new instance of the object that I was trying to Update  Then I passed that object to my reposotory

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In my case  I was using the ASP NET Identity Framework  I had used the built in UserManager FindByNameAsync method to retrieve an ApplicationUser entity  I then tried to reference this entity on a newly created entity on a different DbContext  This resulted in the exception you originally saw   I solved this by creating a new ApplicationUser entity with only the Id from the UserManager method and referencing that new entity

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Alternatively to injection and even worse Singleton  you can call Detach method before Add   EntityFramework 6    IObjectContextAdapter cs  ObjectContext Detach city1    EntityFramework 4  cs Detach city1    There is yet another way  in case you don t need first DBContext object  Just wrap it with using keyword   Payroll Entities City city1  using  CityService cs   new CityService        city1   cs SelectCity Convert ToInt64 cmbCity SelectedItem Value

[c#] entity object cannot be referenced by multiple instances of IEntityChangeTracker. while adding related objects to entity in Entity Framework 4.1

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