We Keep Coding

Why do I get tracking error while updating entity in EF Core? [duplicate]

This question already has answers here:
The instance of entity type cannot be tracked because another instance of this type with the same key is already being tracked
(23 answers)
Closed last month.
I have a model class Patient:
[Key]
[Required(ErrorMessage = "")]
[MinLength(3)]
public string PatientCode { get; set; }
[Required(ErrorMessage = "")]
[MinLength(1)]
public string Name { get; set; }
[Required(ErrorMessage = "")]
[MinLength(1)]
public string Surname { get; set; }
I have a generic repository where I try to update my entity:
public async Task<bool> UpdateAsync(T entity)
{
try
{
_applicationContext.Set<T>().Update(entity);
await _applicationContext.SaveChangesAsync();
return true;
}
catch (Exception)
{
return false;
}
}
which I call from my controller:
private readonly IRepository<Patient> _patientRepository;
...
[HttpPatch("update/")]
public async Task<IActionResult> UpdateAsync([FromBody] Patient patient)
{
var result = await _patientRepository.UpdateAsync(patient);
if (result)
return Ok();
return BadRequest();
}
And when I do so, I get this error:
The instance of entity type 'Patient' cannot be tracked because another instance with the same key value for {'PatientCode'} is already being tracked
If I comment out setting the entity in my repository (comment line _applicationContext.Set<T>().Update(entity);) everything works just fine. It means that my entity has been attached to the ChangeTracker somehow. But how is it possible in such a straight forward code?

The error occurs when a DbContext instance is given an entity reference that it isn't tracking that has a same key value with an entity reference that it is tracking. This can be a common problem in application designs that use Dependency Injection for the DbContext since within the scope of a single repository that gets an injected DbContext it's an unknown what entity references that DbContext might already be tracking. For instance if your code happens to load a different entity that happens to have a reference to that particular Patient record that is either eager or lazy loaded, then passing a different entity reference, such as one that has been deserialized/mapped from a POST payload and calling Update will result in this exception, and it can be situational depending on whether the DbContext happens to be tracking that matching entity or not.
Passing entities around beyond the scope of their DbContext including serialization/deserialization requires extra care when dealing with updating entities and references to related entities. It also means you need to be prepared to deal with tracked references.
Since different entities will likely use different keys, I strongly recommend moving away from the Generic Repository pattern, or at least mitigate it to truly identical lowest-common-denominator type base code. Too many developers end up painting themselves into a tight corner far from the doorway with this anti-pattern.
public async Task<bool> UpdateAsync(Patient patient)
{
try
{ // Going to .Local checks for tracked references, it won't hit the DB.
var trackedReference = _applicationContext.Patients.Local
.SingleOrDefault(p => p.PatientCode == patient.PatientCode);
if (trackedReference == null)
{ // We aren't already tracking an entity so we should be safe to attempt an Update.
_applicationContext.Patients.Update(patient);
}
else if (!Object.ReferenceEquals(trackedReference, patient))
{ // Here we have a bit more work to do. The DbContext is already
// tracking a reference to this Patient and it's *not* the copy
// you are passing in... Need to determine what to do, copy
// values across, etc.
Mapper.Map(patient, trackedReference); // This would use Automapper to copy values into the tracked reference, overwriting.
}
// If the patient passed in is the same reference as the tracked
// instance, nothing to do, just call SaveChanges.
await _applicationContext.SaveChangesAsync();
return true;
}
catch (Exception)
{
return false;
}
}
This may look simple enough, but you need to apply these checks to all entities in the entity graph. So for instance if a Patient references other entities like Address etc. you need to check the DbContext to see if it is already tracking a reference (where that address might be updated or inserted). For references to existing data rows you will want to check and replace references with existing tracked references, or Attach them if not tracked to avoid EF attempting to treat the untracked reference as a new entity and try inserting it.

.NET - Attaching an entity of type failed because another entity of the same type already has the same primary key value

I know there are several questions posed about this very same thing but none of which seems to help me. I'm trying to do a .RemoveRange() and every question I've been seeing has to do with edits and adds.
Here's the relevant bits of the method in which the exception is getting thrown:
public bool UpdateFileboundApplications(IList<IFileboundApplicationDm> fileboundApplications)
{
// get all mappings in the DB that match the incoming fileboundApplications
var incomingFbAppsAlreadyExistingInDb =
fileboundApplications.Where(app => app.Id == Db.inf_DMS_FBApplicationProjectMapping.SingleOrDefault(a => a.ApplicationId == app.Id)?.ApplicationId
&& app.FileboundProject != null).ToList();
// in the case that application/project mappings include filebound applications with no project mapping,
// pass the collection to a method which will handle removal of these records.
var fbAppMappingsWithoutNulls = RemoveNullFileboundApplicationMappings(incomingFbAppsAlreadyExistingInDb, fileboundApplications);
var fbAppMappingsAppIdsAndProjectIds = fbAppMappingsWithoutNulls.Select(x => new { appId = x.Id, projectId = x.FileboundProject.Id}).ToList();
var dbRecords = Db.inf_DMS_FBApplicationProjectMapping.Select(y => new { appId = y.ApplicationId, projectId = y.ProjectID}).ToList();
var fbApplicationDifferences =
dbRecords.FindDifferences(fbAppMappingsAppIdsAndProjectIds,
s => new Tuple<int, int>(s.appId, s.projectId),
d => new Tuple<int, int>(d.appId, d.projectId));
if (fbApplicationDifferences.ExistOnlyInSource.Any())
{
// items to remove from the table, as these apps are now assigned to a different project.
var allAppsToRemove = fbApplicationDifferences.ExistOnlyInSource.Select(x => new inf_DMS_FBApplicationProjectMapping
{
ApplicationId = x.appId,
ProjectID = x.projectId,
MapId = Db.inf_DMS_FBApplicationProjectMapping.Single(m => m.ApplicationId == x.appId).MapId
}).ToList();
Db.inf_DMS_FBApplicationProjectMapping.RemoveRange(allAppsToRemove);
}
Db.SaveChanges();
return true;
}
FWIW, I'll include the code for the RemoveNullFileboundApplicationMappings as well:
private IEnumerable<IFileboundApplicationDm> RemoveNullFileboundApplicationMappings(IEnumerable<IFileboundApplicationDm> incomingFbAppsAlreadyExistingInDb,
IEnumerable<IFileboundApplicationDm> fileboundApplications)
{
// hold a collection of incoming fileboundApplication IDs for apps that have no associated fileboundProject
var appIdsWithNoFbProject = fileboundApplications.Except(incomingFbAppsAlreadyExistingInDb)
.Select(app => app.Id);
// get records in the table that now need to be removed
var dbRecordsWithMatchingIds = Db.inf_DMS_FBApplicationProjectMapping.Where(mapping => appIdsWithNoFbProject.Contains(mapping.ApplicationId));
if (dbRecordsWithMatchingIds.Any())
{
// remove records for apps that no will no longer have an associated Filebound project
Db.inf_DMS_FBApplicationProjectMapping.RemoveRange(dbRecordsWithMatchingIds);
Db.SaveChanges();
}
return fileboundApplications.Where(app => app.FileboundProject != null);
}
Finally, here's the inf_DMS_FBApplicationProjectMapping class:
public partial class inf_DMS_FBApplicationProjectMapping
{
public int MapId { get; set; } // <-- this is the PK
public int ApplicationId { get; set; }
public int ProjectID { get; set; }
public Nullable<int> Modified_By { get; set; }
public Nullable<System.DateTime> Modified_On { get; set; }
public virtual glb_Applications glb_Applications { get; set; }
}
}
Exception reads as follows:
{"Attaching an entity of type 'xxxx' failed because another entity of the same type already has the same primary key value. This can happen when using the 'Attach' method or setting the state of an entity to 'Unchanged' or 'Modified' if any entities in the graph have conflicting key values. This may be because some entities are new and have not yet received database-generated key values.
In this case use the 'Add' method or the 'Added' entity state to track the graph and then set the state of non-new entities to 'Unchanged' or 'Modified' as appropriate."}
I don't quite understand how I need to be using Db.inf_.....Add(), as I'm not intending to add records to the table; I need to be removing records.
I don't understand what this "attaching to context" is all about and what that really means.
I really appreciate any insight the community may have on this. It's been a struggle trying to find a way to solve this. Thanks!

I guess the problem is in the new that you use to compose the list you pass as parameter to RemoveRange. As the entities in that list have not been queried directly from your DbSet they have never been attached to your local context and so EF gets confused.
You need to understand the concept of entities attached to the context. Entity Framework keeps track of the changes done to entities you are working with, in order to be able to decide what to do when you do SaveChanges: insert, update, delete. EF is only able to do that if the entities are attached to the context. That means they have a property State with the value Added, Deleted, Modified, Unchanged, etc.
In simple scenarios this is transparent to you, because entities get automatically attached when you do DbSet.Add(entity), DbSet.Find(entityId), or when you get an entity instance as a result of a query, like DbSet.Where(...), DbSet.FirstOrDefault(...), etc. That is why you probably never had to worry about attached entities before in your EF code.
In more complex scenarios like your current one, the entities you are trying to delete have not been instantiated from one of those operations, so they have not been automatically attached to your context. You have to do it explicitly, if you instantiate them with new.
So you should do something like this before the SaveChanges:
foreach(var item in allAppsToRemove)
{
Db.Entry(item).State = EntityState.Deleted;
}
By using the method Entry the entities get attached to the context, and then you explicity set their state as Deleted, to have them deleted when SaveChanges is executed later.
Take a look at this page. Even if it deals mostly with Add and Update cases it contains information relevant to your problem with the Delete. Understanding the concept of entities attached to the local DbContext will help you a lot when programming with EF. There are some cases like this one where you will have trouble if you don't know how attached entities work (you will eventually get to some 'orphaned children' errors also).
Note: in Entity Framework Core (EF7) there is an AttachRange method that can be used before RemoveRange.

With Diana's help, I was able to solve this issue.
The problem was that I was manually flipping the entity state AND calling .RemoveRange(). I only needed to be flipping the entity state. Here's the relevant bits that solved the issue:
...
...
...
if (fbApplicationDifferences.ExistOnlyInSource.Any())
{
// items to remove from the table, as these apps are now assigned to a different project.
var allAppsToRemove = fbApplicationDifferences.ExistOnlyInSource.Select(x => new inf_DMS_FBApplicationProjectMapping
{
ApplicationId = x.appId,
ProjectID = x.projectId,
MapId = Db.inf_DMS_FBApplicationProjectMapping.Single(m => m.ApplicationId == x.appId).MapId
}).ToList();
foreach (var app in allAppsToRemove)
{
var item = Db.inf_DMS_FBApplicationProjectMapping.Find(app.MapId);
Db.Entry(item).State = EntityState.Deleted;
}
//Db.inf_DMS_FBApplicationProjectMapping.RemoveRange(allAppsToRemove); <-- these items are already "flagged for deletion" with .State property change a few lines above.
}

Just change your code after SaveChanges methot change EntityState Detached

NHibernate by code - Save entity with unsaved(transient) child entity

I have the following entity:
public class Item
{
public virtual long ID { get; set; }
public virtual Version Version { get; set;}
More properties...
}
In the entity mapping I have:
ManyToOne(p => p.Version, m =>
{
m.Column("VERSION_ID");
}
The entity Version is also mapped by code and it's ID is an auto generated sequence.
When I save an Item, I create a new Version, assign it to the Version property and save it. I want to save the Version entity only after the Item is successfully saved. Now it throws a TransientObjectExceptionwhen I do this. Is it possible to solve this?

You cannot save an entity that references a transient object through a mapped property (Item->Version) unless when mapping the property you specify Cascade.Persist or Cascade.All.
Another thing is that since you should be running that code in a transaction the order of inserts should not matter. In case an exception is thrown (or anything else bad happens) after you save Version but before you save the Item, the transaction should be rolled back and nobody is going to see the new version.
The snippet below shows how you can begin/commit a transaction with nHibernate. Notice that the transaction will be rolled back if it does not get commited before it is disposed.
using(var session = sessionFactory.OpenSession())
using(var transaction = session.BeginTransaction())
{
// Do your thing here...
transaction.Commit();
}

Unable to update modified entities

I've got an aggregate for a specific type of entity which is stored in a collection inside the aggregate. Now I'd like to add a new entry of that type and update the aggregate afterwards, however Entity Framework never updates anything!
Model
public class MyAggregate {
protected ICollection<MyEntity> AggregateStorage { get; set; }
public void AddEntity(MyEntity entity) {
// some validation
AggregateStorage.Add(entity);
}
}
API Controller
[UnitOfWork, HttpPost]
public void UpdateMyEntity(int aggregateId, MyEntityDto dto) {
var aggregate = _aggregateRepository.Find(aggregateId);
aggregate.AddEntity(...// some mapping of the dto).
_aggregateRepository.Update(aggregate);
}
EF Update
EntitySet.Attach(aggregate);
Context.Entry(aggregate).State = EntityState.Modified;
(Please note that there's an unit of work interceptor on the API action who fires DbContext.SaveChanges() after successful execution of the method.)
Funny thing is, the update never get's executed by EF. I've added a log interceptor to the DbContext to see what's going on sql-wise and while everything else works fine, an update statement never occurs.

According to this answer in detached scenario (either aggregate is not loaded by EF or it is loaded by different context instance) you must attach the aggregate to context instance and tell it exactly what did you changed, set state for every entity and independent association in object graph.
You must either use eager loading and load all data together at the beginning and
instead of changing the state of aggregate, change the state of entities:
foreach(var entity in aggregate.AggregateStorage)
{
if(entity.Id == 0)
Context.Entry(entity).State = EntityState.Added;
}

Lots of problems (foreign key or no rows were updated errors) when trying to save complex objects in EF code first

I have a pretty deep object hierarchy in my application, and I am having trouble saving the entities. Depending on the order I do things, I either one of two errors:
[OptimisticConcurrencyException: Store update, insert, or delete statement affected an unexpected number of rows (0). Entities may have been modified or deleted since entities were loaded. Refresh ObjectStateManager entries.]
or
[DbUpdateException: An error occurred while saving entities that do not expose foreign key properties for their relationships. The EntityEntries property will return null because a single entity cannot be identified as the source of the exception. Handling of exceptions while saving can be made easier by exposing foreign key properties in your entity types. See the InnerException for details.]
Here is the classes I am working with:
public class SpecialEquipment : Entity
{
public Equipment Equipment { get; set; }
public virtual ICollection<AutoclaveValidation> Validations { get; set; }
}
public class Equipment : Entity
{
public string Model { get; set; }
public string SerialNumber { get; set; }
public Location Location { get; set; }
public EquipmentType EquipmentType { get; set; }
public ICollection<Identifier> Identifiers { get; set; }
}
public class Identifier : Entity
{
public IdentifierType Type { get; set; }
public string Value { get; set; }
}
public class Location : Entity
{
public Building Building { get; set; }
public string Room { get; set; }
}
What I was trying to do was populate one SpecialEquipment object based on form inputs and already existing objects in the database and then save the special equipment to push all changes through, it looks like this:
Building building = buildingService.GetExistingOrNew(viewModel.BuildingCode)); //checks to see if building exists already, if not, create it, save it, and re-query
Location location = locationService.GetExistingOrNew(viewModel.Room, building); //checks to see if location exists already, if not, create it, save it, and re-query
EquipmentType equipmentType = equipmentTypeService.GetOne(x => x.Name == EquipmentTypeConstants.Names.Special);
Equipment equipment = new Equipment{ EquipmentType = equipmentType, Location = location };
equipment.Identifiers = new Collection<Identifier>();
foreach (FormIdentifier formIdentifier in identifiers)
{
FormIdentifier fIdentifier = formIdentifier;
IdentifierType identifierType = identifierTypeService.GetOne(x => x.Id == fIdentifier.Key);
equipment.Identifiers.Add(new Identifier { Type = identifierType, Value = fIdentifier.Value });
}
EntityServiceFactory.GetService<EquipmentService>().Save(equipment);
SpecialEquipment specialEquipment = new SpecialEquipment();
specialEquipment.Equipment = equipment;
specialEquipmentService.Save(specialEquipment);
This code returns Store update, insert, or delete statement affected an unexpected number of rows (0). If I comment out the foreach identifiers OR put the foreach identifiers after the equipment save and then call equipment save after the loop the code works. If I comment out the foreach identifiers and the save equipment line, I get : The INSERT statement conflicted with the FOREIGN KEY constraint "SpeicalEquipment_Equipment". The conflict occurred in database "xxx", table "dbo.Equipments", column 'Id'.
So how can I make these errors not occur but still save my object? Is there a better way to do this? Also I don't like saving my equipment object, then associating/saving my identifiers and/or then my special equipment object because if there is an error occurring between those steps I will have orphaned data. Can someone help?
I should mention a few things that aren't inheritly clear from code, but were some answers I saw for similar questions:
My framework stores the context in the HttpContext, so all the service methods I am using in my API are using the same context in this block of code. So all objects are coming from/being stored in one context.
My Entity constructor populates ID anytime a new object is created, no entities have a blank primary key.
Edit: At the request of comments:
My .Save method calls Insert or Update depending on if the entity exists or not (in this example insert is called since the specialEquipment is new):
public void Insert(TClass entity)
{
if (Context.Entry(entity).State == EntityState.Detached)
{
Context.Set<TClass>().Attach(entity);
}
Context.Set<TClass>().Add(entity);
Context.SaveChanges();
}
public void Update(TClass entity)
{
DbEntityEntry<TClass> oldEntry = Context.Entry(entity);
if (oldEntry.State == EntityState.Detached)
{
Context.Set<TClass>().Attach(oldEntry.Entity);
}
oldEntry.CurrentValues.SetValues(entity);
//oldEntry.State = EntityState.Modified;
Context.SaveChanges();
}
GetExistingOrNew for Building and location both are identical in logic:
public Location GetExistingOrNew(string room, Building building)
{
Location location = GetOne(x => x.Building.Code == building.Code && x.Room == room);
if(location == null)
{
location = new Location {Building = building, Room = room};
Save(location);
location = GetOne(x => x.Building.Code == building.Code && x.Room == room);
}
return location;
}
Get one just passes that where predicate to the context in my repository with singleOrDefault. I am using a Service Layer/Repository Layer/Object Layer format for my framework.

Your Insert method does not seem to be correct:
public void Insert(TClass entity)
{
if (Context.Entry(entity).State == EntityState.Detached)
Context.Set<TClass>().Attach(entity);
Context.Set<TClass>().Add(entity);
Context.SaveChanges();
}
specialEquipment is a new entity and the related specialEquipment.Equipment as well (you are creating both with new)
Look what happens if you pass in the specialEquipment into the Insert method:
specialEquipment is detached because it is new
So, you attach it to the context
Attach attaches specialEquipment and the related specialEquipment.Equipment as well because both were detached from the context
Both are in state Unchanged now.
Now you add specialEquipment: This changes the state of specialEquipment to Added but not the state of specialEquipment.Equipment, it is still Unchanged.
Now you call SaveChanges: EF creates an INSERT for the added entity specialEquipment. But because specialEquipment.Equipment is in state Unchanged, it doesn't INSERT this entity, it just sets the foreign key in specialEquipment
But this FK value doesn't exist (because specialEquipment.Equipment is actually new as well)
Result: You get the FK constraint violation.
You are trying to fix the problem with calling Save for the equipment but you have the same problem with the new identifiers which will finally throw an exception.
I think your code should work if you add the specialEquipment (as the root of the object graph) at the end once to the context - without attaching it, so that the whole graph of new objects gets added, basically just:
context.Set<SpecialEquipment>().Add(specialEquipment);
context.SaveChanges();
(BTW: Your Update also doesn't look correct, you are just copying every property of entity to itself. The context won't detect any change and SaveChanges won't write any UPDATE statement to the database.)

My guess? It can't have an ID if you haven't saved it and that's the root of the problem (since it works if you save first).
Pop everything in a transaction, so if anything goes wrong all is rolled back. Then you don't have orphans.
See http://msdn.microsoft.com/en-us/library/bb738523.aspx for how to use transactions with EF.