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Error The instance of entity type ModalType cannot be tracked because another instance with the key value {id: 7656544} is already being tracked.

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Question: How do you solve the Entity Framework Error that says: "Error The instance of entity type ModalType cannot be tracked because another instance with the key value {id: 7656544} is already being tracked. When attaching existing entities, ensure that only one entity with a given key value is attached.


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Answer:
Take a look around your class and find where you are referencing the same entity twice. If you are checking to see if the Entity Exists in the database by using the following code

MyEntity myEntity = _context.MyEntity.FirstOrDefault();
bool doesMyEntityExistInDatabase = _context.MyEntity.Any(a=>a.Id ==myEntity.Id);

//Then trying to modify MyEntity like this
myEntity.Name = "SomeNamesInHere";
_context.SaveChanges();

This might throw an error saying the Entity is being tracked already. Instead do not reference the myEntity in any of the boolean code.

[Important]: When you load your database Modals into the Database Context without using AsNoTracking(), Entity Framework Core automatically Tracks All the Entities/Modals/POCO Classes. However, in order to avoid the error "The instance of entity type ModalType cannot be tracked because another instance with the key value {id: 7656544} is already being tracked." in MVC AspNet 6 you need only to SaveChanges() and not attempt to Track the Entity you are trying to modify.

1. When you do _context.MyEntity.Update(NewEntity); you are telling EF Core 6 to track the Entity AGAIN!! which is why that error happens. Instead, just Save the Changes.

2. If the Changes don't get committed or Saved to the Database, try to retrieve a fresh Entity from the Database Context then operate on that Entity by:

var MyEntity = _context.MyEntity.Where(a => a.id = id).FirstOrDefault();
MyEnitity.Name = "NameHere";

_context.SaveChanges();

That way the EF Core will not make a round trip to the Database to fetch MyEntity since it is already tracked it will retrieve it from the Memory Cache. 

[Updated: 9/12/22]
Another Example would be, if are trying to update the Entity that is already tracked by the Database Tracker, this will throw. Take a look below:

1. Retrieve the Entity from the Database
    - This will track the Entity unless you append AsNoTracking() to the Predicate Query, keep in mind that when you append AsNoTracking that you don't try to make changes to the retrieved Entity then try to commit changes to the database otherwise you will pay a very heavy cost.

2. Modify the Entity and then call _context.Update(MyEntity), and BOOOM! this throws because when you call Update() you are trying to tack the MyEntity
    that is already being tracked.


[NB]: Try this instead:
1. Fetch the Entity from the Database without appending AsNoTracking(), this tells EF Core that it should track the Entity because you will be making
    modifications to the Entity itself.
- There are benefits of tracking Entities, 
     1). You don't have to worry about when to commit the changes, the Entity Framework ChangeTracker keeps tabs of what is happening to the tracked Entities and when
          you feel like committing or saving changes to the database, the EF Core bundles all that together and saves the changes to the Database.
          - That is the beauty of using Entity Framework in the nutshell.

2. Make changes to the Entity retrieved from the database and then call SaveChanges().
    - Do not call Update() because it will throw.



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Jack said:

Hey ErnesTech, thank you this helped alot.

Posted On: March 16, 2022 14:08:11 PM

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