The instance of entity type cannot be tracked because another instance with the same key value for {‘Id’} is already being tracked

When using Entity Framework (EF) Core, by default, EF Core will track any records that it pulls from the database so that it can tell if it has changes when you go to save it again. If you attempt to add the same record again etc, it will complain with a “The instance of entity type cannot be tracked because another instance with the same key value for {‘Id’} is already being tracked” error.

If you do N-Tier development, then having EF track your objects in the Repository or DataLayer of your API is of no use. It will start to cause problems when you go to save the object through a different endpoint that has created a copy of the repository model and a SaveChanges() is attempted.

In order to work around this, you can declare the Dependency Injected (DI) instance of your DB context to not use Query Tracking by using this type of code in your Startup.cs.

services.AddDbContext<AppLogContext>(o => 
o.UseSqlServer(_AppLoggingConnString)
.UseQueryTrackingBehavior(QueryTrackingBehavior.NoTracking));

You can also accomplish this on each and every query, especially if your not using .NET Core and/or Dependency Injection as:

var _entityrows = (from al in _ale.AppLogs
                   select al).AsNoTracking();

You also have the option to set this behavior on the context at some other point in your code:

 _ale.AppLogs.QueryTrackingBehavior = QueryTrackingBehavior.NoTracking;

Thanks for Reading!

Author: Jack Yasgar

Jack Yasgar has been developing software for various industries for two decades. Currently, he utilizes C#, JQuery, JavaScript, SQL Server with stored procedures and/or Entity Framework to produce MVC responsive web sites that converse to a service layer utilizing RESTful API in Web API 2.0 or Microsoft WCF web services. The infrastructure can be internal, shared or reside in Azure. Jack has designed dozens of relational databases that use the proper primary keys and foreign keys to allow for data integrity moving forward. While working in a Scrum/Agile environment, he is a firm believer that quality software comes from quality planning. Without getting caught up in analysis paralysis, it is still possible to achieve a level of design that allows an agile team to move forward quickly while keeping re-work to a minimum. Jack believes, “The key to long term software success is adhering to the SOLID design principles. Software written quickly, using wizards and other methods can impress the business sponsor / product owner for a short period of time. Once the honeymoon is over, the product owner will stay enamored when the team can implement changes quickly and fix bugs in minutes, not hours or days.” Jack has become certified by the Object Management Group as OCUP II (OMG Certified UML Professional) in addition to his certification as a Microsoft Certified Professional. The use of the Unified Modeling Language (UML) provides a visual guide to Use Cases and Activities that can guide the product owner in designing software that meets the end user needs. The software development teams then use the same drawings to create their Unit Tests to make sure that the software meets all those needs. The QA testing team can use the UML drawings as a guide to produce test cases. Once the software is in production, the UML drawings become a reference for business users and support staff to know what decisions are happening behind the scenes to guide their support efforts.

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