The relationship could not be changed because one or more of the foreign-key properties is non-nullable

Question

I am getting this error when I GetById() on an entity and then set the collection of child entities to my new list which comes from the MVC view.

The operation failed: The relationship could not be changed because one or more of the foreign-key properties is non-nullable. When a change is made to a relationship, the related foreign-key property is set to a null value. If the foreign-key does not support null values, a new relationship must be defined, the foreign-key property must be assigned another non-null value, or the unrelated object must be deleted.

I don't quite understand this line:

The relationship could not be changed because one or more of the foreign-key properties is non-nullable.

Why would I change the relationship between 2 entities? It should remain the same throughout the lifetime of the whole application.

The code the exception occurs on is simple assigning modified child classes in a collection to the existing parent class. This would hopefully cater for removal of child classes, addition of new ones and modifications. I would have thought Entity Framework handles this.

The lines of code can be distilled to:

var thisParent = _repo.GetById(1);
thisParent.ChildItems = modifiedParent.ChildItems();
_repo.Save();

Rhizo

I found my answer buy using solution #2 in the below article, basically I created added a primary key to the child table for the reference to the parent table (so it has 2 primary keys (the foreign key for the parent table and the ID for the child table). c-sharpcorner.com/UploadFile/ff2f08/… – Meris

@jaffa, I found my answer here #22858991 – Left

For me the fix was simple. My db foreign key column is a nullable int, but my EF property was an int. I made it an int? to match the db and problem solved. – Acquit

Answer 1

You should delete old child items thisParent.ChildItems one by one manually. Entity Framework doesn't do that for you. It finally cannot decide what you want to do with the old child items - if you want to throw them away or if you want to keep and assign them to other parent entities. You must tell Entity Framework your decision. But one of these two decisions you HAVE to make since the child entities cannot live alone without a reference to any parent in the database (due to the foreign key constraint). That's basically what the exception says.

Edit

What I would do if child items could be added, updated and deleted:

public void UpdateEntity(ParentItem parent)
{
    // Load original parent including the child item collection
    var originalParent = _dbContext.ParentItems
        .Where(p => p.ID == parent.ID)
        .Include(p => p.ChildItems)
        .SingleOrDefault();
    // We assume that the parent is still in the DB and don't check for null

    // Update scalar properties of parent,
    // can be omitted if we don't expect changes of the scalar properties
    var parentEntry = _dbContext.Entry(originalParent);
    parentEntry.CurrentValues.SetValues(parent);

    foreach (var childItem in parent.ChildItems)
    {
        var originalChildItem = originalParent.ChildItems
            .Where(c => c.ID == childItem.ID && c.ID != 0)
            .SingleOrDefault();
        // Is original child item with same ID in DB?
        if (originalChildItem != null)
        {
            // Yes -> Update scalar properties of child item
            var childEntry = _dbContext.Entry(originalChildItem);
            childEntry.CurrentValues.SetValues(childItem);
        }
        else
        {
            // No -> It's a new child item -> Insert
            childItem.ID = 0;
            originalParent.ChildItems.Add(childItem);
        }
    }

    // Don't consider the child items we have just added above.
    // (We need to make a copy of the list by using .ToList() because
    // _dbContext.ChildItems.Remove in this loop does not only delete
    // from the context but also from the child collection. Without making
    // the copy we would modify the collection we are just interating
    // through - which is forbidden and would lead to an exception.)
    foreach (var originalChildItem in
                 originalParent.ChildItems.Where(c => c.ID != 0).ToList())
    {
        // Are there child items in the DB which are NOT in the
        // new child item collection anymore?
        if (!parent.ChildItems.Any(c => c.ID == originalChildItem.ID))
            // Yes -> It's a deleted child item -> Delete
            _dbContext.ChildItems.Remove(originalChildItem);
    }

    _dbContext.SaveChanges();
}

Note: This is not tested. It's assuming that the child item collection is of type ICollection. (I usually have IList and then the code looks a bit different.) I've also stripped away all repository abstractions to keep it simple.

I don't know if that is a good solution, but I believe that some kind of hard work along these lines must be done to take care of all kinds of changes in the navigation collection. I would also be happy to see an easier way of doing it.

Theroid

So what if some are only changed? Does that mean I still have to remove them and add them again? – Rhizo

@Jon: No, you can also update existing items of course. I've added an example how I would probably update the child collection, see Edit section above. – Theroid

@Slauma: Lol, if I knew that you are going to modify your answer I would not write my answer ... – Peoria

@Ladislav: No, no, I am glad that you wrote your own answer. Now at least I know that it's not complete nonsense and much too complicated what I did above. – Theroid

@Slauma: I've tried out the above code and it looks good, however I run into a problem in the removing items in the collection. The error is: "Collection was modified; enumeration operation may not execute". Any ideas how to get around this? – Rhizo

@Jon: Try to append a ToList() after the Where method: ....Where(c => c.ID != 0).ToList(). – Theroid

@Jon: I've changed to code to add ToList() and wrote a comment into the sample. It's indeed necessary to make a copy with ToList() because removing from the context removes also from the collection internally. – Theroid

@Slauma: Yes I realised that Remove() modifies the existing enumeration hence either using the ToList() in the for loop or using a separate 'var y = x.toList() then using y in the for()'. Thanks again! – Rhizo

Because you are doing nested loops the performance on this could become an issue if the set of data to update is sufficiently large. An alternative approach is to sort the data by the key and then loop through the two sets of data one item at a time to determine whether you need to add, update, or delete the item. – Anticholinergic

would it be easier to delete all child items and then recreate them?, or would this be slower than the nested loops? – Shuster

@SOfanatic: In cases where you have other entities referencing a child entity it won't be possible to delete it. – Theroid

@Slauma: yes I meant in the case where there is a one-to-many relationship between the parent and the children, so if the parent is deleted, all children should be deleted too. – Shuster

I would add a condition when retrieving the originalChildItem in the foreach: ...Where(c => c.ID == childItem.ID && c.ID != 0) otherwise it will return the newly added children if the childItem.ID == 0. – Jeopardous

@perfect_element: You are absolutely right. That was an almost 3 years old serious bug in the code. Thanks! – Theroid

Trying to get this working myself wasted over a week, thanks for posting. EF need to try and handle this themselves. – Cammi

@Theroid Do you know how can we do this by using repositories ? That means without using _dbContext directly. – Margarettamargarette

What is the WillCascadeOnDelete() option for then? – Sicklebill

I faced same problem and same question in my mind as like @jaffa. But from first paragraph of this answer it's more clear what EF trying to say. Thanks for explanation and answer ! – Fluker

Answer 2

The reason you're facing this is due to the difference between composition and aggregation.

In composition, the child object is created when the parent is created and is destroyed when its parent is destroyed. So its lifetime is controlled by its parent. e.g. A blog post and its comments. If a post is deleted, its comments should be deleted. It doesn't make sense to have comments for a post that doesn't exist. Same for orders and order items.

In aggregation, the child object can exist irrespective of its parent. If the parent is destroyed, the child object can still exist, as it may be added to a different parent later. e.g.: the relationship between a playlist and the songs in that playlist. If the playlist is deleted, the songs shouldn't be deleted. They may be added to a different playlist.

The way Entity Framework differentiates aggregation and composition relationships is as follows:

• For composition: it expects the child object to a have a composite primary key (ParentID, ChildID). This is by design as the IDs of the children should be within the scope of their parents.

• For aggregation: it expects the foreign key property in the child object to be nullable.

So, the reason you're having this issue is because of how you've set your primary key in your child table. It should be composite, but it's not. So, Entity Framework sees this association as aggregation, which means, when you remove or clear the child objects, it's not going to delete the child records. It'll simply remove the association and sets the corresponding foreign key column to NULL (so those child records can later be associated with a different parent). Since your column does not allow NULL, you get the exception you mentioned.

Solutions:

1- If you have a strong reason for not wanting to use a composite key, you need to delete the child objects explicitly. And this can be done simpler than the solutions suggested earlier:

context.Children.RemoveRange(parent.Children);

2- Otherwise, by setting the proper primary key on your child table, your code will look more meaningful:

parent.Children.Clear();

Obligation

I found this explanation most helpful. – Ratfink

Good explanation for composition vs aggregation and how entity framework is relates to it. – Jijib

#1 was the least amount of code necessary to fix the issue. Thank you! – Piscine

Actually sometimes using composite key bring complexity into the program and it is better to only have one identity column. medium.com/@pablodalloglio/… – Chicanery

Ohhh my God !!! that's Mosh Hamedani !!! :D – Fiddlededee

Answer 3

This is a very big problem. What actually happens in your code is this:

• You load Parent from the database and get an attached entity
• You replace its child collection with new collection of detached children
• You save changes but during this operation all children are considered as added becasue EF didn't know about them till this time. So EF tries to set null to foreign key of old children and insert all new children => duplicate rows.

Now the solution really depends on what you want to do and how would you like to do it?

If you are using ASP.NET MVC you can try to use UpdateModel or TryUpdateModel.

If you want just update existing children manually, you can simply do something like:

foreach (var child in modifiedParent.ChildItems)
{
    context.Childs.Attach(child); 
    context.Entry(child).State = EntityState.Modified;
}

context.SaveChanges();

Attaching is actually not needed (setting the state to Modified will also attach the entity) but I like it because it makes the process more obvious.

If you want to modify existing, delete existing and insert new childs you must do something like:

var parent = context.Parents.GetById(1); // Make sure that childs are loaded as well
foreach(var child in modifiedParent.ChildItems)
{
    var attachedChild = FindChild(parent, child.Id);
    if (attachedChild != null)
    {
        // Existing child - apply new values
        context.Entry(attachedChild).CurrentValues.SetValues(child);
    }
    else
    {
        // New child
        // Don't insert original object. It will attach whole detached graph
        parent.ChildItems.Add(child.Clone());
    }
}

// Now you must delete all entities present in parent.ChildItems but missing
// in modifiedParent.ChildItems
// ToList should make copy of the collection because we can't modify collection
// iterated by foreach
foreach(var child in parent.ChildItems.ToList())
{
    var detachedChild = FindChild(modifiedParent, child.Id);
    if (detachedChild == null)
    {
        parent.ChildItems.Remove(child);
        context.Childs.Remove(child); 
    }
}

context.SaveChanges();

Peoria

But there is your interesting remark about using .Clone(). Do you have the case in mind that a ChildItem has other sub-child navigation properties? But in that case, wouldn't we want that the whole sub-graph is attached to the context since we would expect that all the sub-childs are new objects if the child itself is new? (Well, might be different from model to model, but let's assume the case that the sub-childs are "dependent" from the child like the childs are dependent from the parent.) – Theroid

It would probably require "smart" clone. – Peoria

What if you don't want to have a Child's collection in your context? http://stackoverflow.com/questions/20233994/do-i-need-to-create-a-dbset-for-every-table-so-that-i-can-persist-child-entitie – Catfall

parent.ChildItems.Remove(child); context.Childs.Remove(child); This double remove fixed may issue, THANKS. Why do we need both removes? Why removeing just from parent.ChildItems is not enougth since childs only lives as childs? – Kinch

Thanks for this useful code. my problem solved . – Osy

Thanks for this insight. The problem that I had was that when I was updating a database item, that I dit Parent.List<itemType> = new List<itemType>() while the orginal list still contained items that required a parent. THANKS ! – Levorotatory

Answer 4

I found this answer much more helpful for the same error. It seems that EF does not like it when you Remove, it prefers Delete.

You can delete a collection of records attached to a record like this.

order.OrderDetails.ToList().ForEach(s => db.Entry(s).State = EntityState.Deleted);

In the example, all of the Detail records attached to an Order have their State set to Delete. (In preparation to Add back updated Details, as part of an Order update)

Ebby

I believe it's the proper answer. – Toni

logical and straightforward solution. – Hives

solved the problem for me beautifully; by far the best/most elegant solution here – Melburn

Answer 5

I've no idea why the other two answers are so popular!

I believe you were right in assuming the ORM framework should handle it - after all, that is what it promises to deliver. Otherwise your domain model gets corrupted by persistence concerns. NHibernate manages this happily if you setup the cascade settings correctly. In Entity Framework it is also possible, they just expect you to follow better standards when setting up your database model, especially when they have to infer what cascading should be done:

You have to define the parent - child relationship correctly by using an "identifying relationship".

If you do this, Entity Framework knows the child object is identified by the parent, and therefore it must be a "cascade-delete-orphans" situation.

Other than the above, you might need to (from NHibernate experience)

thisParent.ChildItems.Clear();
thisParent.ChildItems.AddRange(modifiedParent.ChildItems);

instead of replacing the list entirely.

UPDATE

@Slauma's comment reminded me that detached entities are another part of the overall problem. To solve that, you can take the approach of using a custom model binder that constructs your models by attempting to load it from the context. This blog post shows an example of what I mean.

Campfire

Setup as identifying relationship won't help here because the scenario in the question has to deal with detached entities ("my new list which comes from the MVC view"). You still have to load the original children from the DB, find the removed items in that collection based on the detached collection and then remove from the DB. The only difference is that with an identifying relationship you can call parent.ChildItems.Remove instead of _dbContext.ChildItems.Remove. There is still (EF <= 6) no built-in support from EF to avoid lengthy code like the one in the other answers. – Theroid

I understand your point. However, I believe with a custom model binder that loads the entity from the context or returns a new instance the approach above would work. I'll update my answer to suggest that solution. – Campfire

Yes, you could use a model binder but you had to do the stuff from the other answers in the model binder now. It just moves the problem from repo/service layer to the model binder. At least, I don't see a real simplification. – Theroid

The simplification is automatic deletion of orphaned entities. All you need in the model binder is a generic equivalent of return context.Items.Find(id) ?? new Item() – Campfire

Good feedback for the EF team, but your proposed solution doesn't solve anything in EF land unfortunately. – Dobbs

How so? I implemented this and is being used as is in production software. – Campfire

Answer 6

If you are using AutoMapper with Entity Framework on the same class, you might hit this problem. For instance if your class is

class A
{
    public ClassB ClassB { get; set; }
    public int ClassBId { get; set; }
}

AutoMapper.Map<A, A>(input, destination);

This will try to copy both properties. In this case, ClassBId is non Nullable. Since AutoMapper will copy destination.ClassB = input.ClassB; this will cause a problem.

Set your AutoMapper to Ignore ClassB property.

 cfg.CreateMap<A, A>()
     .ForMember(m => m.ClassB, opt => opt.Ignore()); // We use the ClassBId

Arva

I'm facing a similar issue with AutoMapper, but this doesn't work for me :( See https://mcmap.net/q/120622/-update-entity-from-viewmodel-in-mvc-using-automapper/613605 – Hose

Answer 7

I had same problem, but I knew it had worked OK in other cases, so I reduced the problem to this:

parent.OtherRelatedItems.Clear();  //this worked OK on SaveChanges() - items were being deleted from DB
parent.ProblematicItems.Clear();   // this was causing the mentioned exception on SaveChanges()

• OtherRelatedItems had a composite Primary Key (parentId + some local column) and worked OK
• ProblematicItems had their own single-column Primary Key, and the parentId was only a FK. This was causing the exception after Clear().

All I had to do was to make the ParentId a part of composite PK to indicate that the children can't exist without a parent. I used DB-first model, added the PK and marked the parentId column as EntityKey (so, I had to update it both in DB and EF - not sure if EF alone would be enough).

Once you think about it, it's a very elegant distinction that EF uses to decide if children "make sense" without a parent (in this case Clear() won't delete them and throw exception unless you set the ParentId to something else/special), or - like in the original question - we expect the items to be deleted once they are removed from the parent.

Gorden

+1 Great answer, I ran into this problem today and could not figure it out. Followed your solution (making ID and Foreign Key column a composite PK and my .Clear() operation finally worked. Thanks. – Hercules

Thanks! I suffered for 3 hours. This is the shortest solution – Broderic

This seems to be exactly the same problem as I have. My issue with the solution is that from a DB design perspective, the composite key isn't quite right. If I'm going to add the equivalent of your ParentId column to the PK, I'll also need to add a UNIQUE constraint on the other column to ensure that it remains unique and data integrity is maintained. At the moment, the PK constraint is doing this. – Cartesian

Answer 8

I just had the same error. I have two tables with a parent child relationship, but I configured a "on delete cascade" on the foreign key column in the table definition of the child table. So when I manually delete the parent row (via SQL) in the database it will automatically delete the child rows.

However this did not work in EF, the error described in this thread showed up. The reason for this was, that in my entity data model (edmx file) the properties of the association between the parent and the child table were not correct. The End1 OnDelete option was configured to be none ("End1" in my model is the end which has a multiplicity of 1).

I manually changed the End1 OnDelete option to Cascade and than it worked. I do not know why EF is not able to pick this up, when I update the model from the database (I have a database first model).

For completeness, this is how my code to delete looks like:

   public void Delete(int id)
    {
        MyType myObject = _context.MyTypes.Find(id);

        _context.MyTypes.Remove(myObject);
        _context.SaveChanges(); 
   }    

If I hadn´t a cascade delete defined, I would have to delete the child rows manually before deleting the parent row.

Gumption

Answer 9

This happens because the Child Entity is marked as Modified instead of Deleted.

And the modification that EF does to the Child Entity when parent.Remove(child) is executed, is simply setting the reference to its parent to null.

You can check the child's EntityState by typing the following code into Visual Studio's Immediate Window when the exception occurs, after executing SaveChanges():

_context.ObjectStateManager.GetObjectStateEntries(System.Data.EntityState.Modified).ElementAt(X).Entity

where X should be replaced by the deleted Entity.

If you don't have access to the ObjectContext to execute _context.ChildEntity.Remove(child), you can solve this issue by making the foreign key a part of the primary key on the child table.

Parent
 ________________
| PK    IdParent |
|       Name     |
|________________|

Child
 ________________
| PK    IdChild  |
| PK,FK IdParent |
|       Name     |
|________________|

This way, if you execute parent.Remove(child), EF will correctly mark the Entity as Deleted.

Houstonhoustonia

Answer 10

This type of solution did the trick for me:

Parent original = db.Parent.SingleOrDefault<Parent>(t => t.ID == updated.ID);
db.Childs.RemoveRange(original.Childs);
updated.Childs.ToList().ForEach(c => original.Childs.Add(c));
db.Entry<Parent>(original).CurrentValues.SetValues(updated);

Its important to say that this deletes all the records and insert them again. But for my case (less then 10) it´s ok.

I hope it helps.

Sholeen

Does the reinsertion happens with new IDs or it keeps the child's IDs they had in the first place? – Disaccredit

Answer 11

I ran into this problem today and wanted to share my solution. In my case, the solution was to delete the Child items before getting the Parent from the database.

Previously I was doing it like in the code below. I will then get the same error listed in this question.

var Parent = GetParent(parentId);
var children = Parent.Children;
foreach (var c in children )
{
     Context.Children.Remove(c);
}
Context.SaveChanges();

What worked for me, is to get the children items first, using the parentId (foreign key) and then delete those items. Then I can get the Parent from the database and at that point, it should not have any children items anymore and I can add new children items.

var children = GetChildren(parentId);
foreach (var c in children )
{
     Context.Children.Remove(c);
}
Context.SaveChanges();

var Parent = GetParent(parentId);
Parent.Children = //assign new entities/items here

Porett

Answer 12

You must manually clear the ChildItems collection and append new items into it:

thisParent.ChildItems.Clear();
thisParent.ChildItems.AddRange(modifiedParent.ChildItems);

After that you can call DeleteOrphans extension method which will handle with orphaned entities (it must be called between DetectChanges and SaveChanges methods).

public static class DbContextExtensions
{
    private static readonly ConcurrentDictionary< EntityType, ReadOnlyDictionary< string, NavigationProperty>> s_navPropMappings = new ConcurrentDictionary< EntityType, ReadOnlyDictionary< string, NavigationProperty>>();

    public static void DeleteOrphans( this DbContext source )
    {
        var context = ((IObjectContextAdapter)source).ObjectContext;
        foreach (var entry in context.ObjectStateManager.GetObjectStateEntries(EntityState.Modified))
        {
            var entityType = entry.EntitySet.ElementType as EntityType;
            if (entityType == null)
                continue;

            var navPropMap = s_navPropMappings.GetOrAdd(entityType, CreateNavigationPropertyMap);
            var props = entry.GetModifiedProperties().ToArray();
            foreach (var prop in props)
            {
                NavigationProperty navProp;
                if (!navPropMap.TryGetValue(prop, out navProp))
                    continue;

                var related = entry.RelationshipManager.GetRelatedEnd(navProp.RelationshipType.FullName, navProp.ToEndMember.Name);
                var enumerator = related.GetEnumerator();
                if (enumerator.MoveNext() && enumerator.Current != null)
                    continue;

                entry.Delete();
                break;
            }
        }
    }

    private static ReadOnlyDictionary<string, NavigationProperty> CreateNavigationPropertyMap( EntityType type )
    {
        var result = type.NavigationProperties
            .Where(v => v.FromEndMember.RelationshipMultiplicity == RelationshipMultiplicity.Many)
            .Where(v => v.ToEndMember.RelationshipMultiplicity == RelationshipMultiplicity.One || (v.ToEndMember.RelationshipMultiplicity == RelationshipMultiplicity.ZeroOrOne && v.FromEndMember.GetEntityType() == v.ToEndMember.GetEntityType()))
            .Select(v => new { NavigationProperty = v, DependentProperties = v.GetDependentProperties().Take(2).ToArray() })
            .Where(v => v.DependentProperties.Length == 1)
            .ToDictionary(v => v.DependentProperties[0].Name, v => v.NavigationProperty);

        return new ReadOnlyDictionary<string, NavigationProperty>(result);
    }
}

Proximo

This worked well for me. I just needed to add context.DetectChanges();. – Confusion

Answer 13

I've tried these solutions and many others, but none of them quite worked out. Since this is the first answer on google, I'll add my solution here.

The method that worked well for me was to take relationships out of the picture during commits, so there was nothing for EF to screw up. I did this by re-finding the parent object in the DBContext, and deleting that. Since the re-found object's navigation properties are all null, the childrens' relationships are ignored during the commit.

var toDelete = db.Parents.Find(parentObject.ID);
db.Parents.Remove(toDelete);
db.SaveChanges();

Note that this assumes the foreign keys are setup with ON DELETE CASCADE, so when the parent row is removed, the children will be cleaned up by the database.

Reexamine

Answer 14

I used Mosh's solution, but it was not obvious to me how to implement the composition key correctly in code first.

So here is the solution:

public class Holiday
{
    [Key, Column(Order = 0), DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int HolidayId { get; set; }
    [Key, Column(Order = 1), ForeignKey("Location")]
    public LocationEnum LocationId { get; set; }

    public virtual Location Location { get; set; }

    public DateTime Date { get; set; }
    public string Name { get; set; }
}

Worse

Answer 15

If you are using Auto mapper and facing the the issue following is the good solution, it work for me

https://www.codeproject.com/Articles/576393/Solutionplusto-aplus-Theplusoperationplusfailed

Since the problem is that we're mapping null navigation properties, and we actually don't need them to be updated on the Entity since they didn't changed on the Contract, we need to ignore them on the mapping definition:

ForMember(dest => dest.RefundType, opt => opt.Ignore())

So my code ended up like this:

Mapper.CreateMap<MyDataContract, MyEntity>
ForMember(dest => dest.NavigationProperty1, opt => opt.Ignore())
ForMember(dest => dest.NavigationProperty2, opt => opt.Ignore())
.IgnoreAllNonExisting();

Logo

Answer 16

This issue arise because we try to delete the parent table still child table data is present. We solve the problem with help of cascade delete.

In model Create method in dbcontext class.

 modelBuilder.Entity<Job>()
                .HasMany<JobSportsMapping>(C => C.JobSportsMappings)
                .WithRequired(C => C.Job)
                .HasForeignKey(C => C.JobId).WillCascadeOnDelete(true);
            modelBuilder.Entity<Sport>()
                .HasMany<JobSportsMapping>(C => C.JobSportsMappings)
                  .WithRequired(C => C.Sport)
                  .HasForeignKey(C => C.SportId).WillCascadeOnDelete(true);

After that,In our API Call

var JobList = Context.Job                       
          .Include(x => x.JobSportsMappings)                                     .ToList();
Context.Job.RemoveRange(JobList);
Context.SaveChanges();

Cascade delete option delete the parent as well parent related child table with this simple code. Make it try in this simple way.

Remove Range which used for delete the list of records in the database Thanks

Christenson

Answer 17

I also solved my problem with Mosh's answer and I thought PeterB's answer was a bit of since it used an enum as foreign key. Remember that you will need to add a new migration after adding this code.

I can also recommend this blog post for other solutions:

http://www.kianryan.co.uk/2013/03/orphaned-child/

Code:

public class Child
{
    [Key, Column(Order = 0), DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int Id { get; set; }

    public string Heading { get; set; }
    //Add other properties here.

    [Key, Column(Order = 1)]
    public int ParentId { get; set; }

    public virtual Parent Parent { get; set; }
}

Rachelrachele

Answer 18

Using the solution of Slauma, I created some generic functions to help update child objects and collections of child objects.

All my persistent objects implement this interface

/// <summary>
/// Base interface for all persisted entries
/// </summary>
public interface IBase
{
    /// <summary>
    /// The Id
    /// </summary>
    int Id { get; set; }
}

With this I implemented these two functions in my Repository

    /// <summary>
    /// Check if orgEntry is set update it's values, otherwise add it
    /// </summary>
    /// <param name="set">The collection</param>
    /// <param name="entry">The entry</param>
    /// <param name="orgEntry">The original entry found in the database (can be <code>null</code> is this is a new entry)</param>
    /// <returns>The added or updated entry</returns>
    public T AddOrUpdateEntry<T>(DbSet<T> set, T entry, T orgEntry) where T : class, IBase
    {
        if (entry.Id == 0 || orgEntry == null)
        {
            entry.Id = 0;
            return set.Add(entry);
        }
        else
        {
            Context.Entry(orgEntry).CurrentValues.SetValues(entry);
            return orgEntry;
        }
    }

    /// <summary>
    /// check if each entry of the new list was in the orginal list, if found, update it, if not found add it
    /// all entries found in the orignal list that are not in the new list are removed
    /// </summary>
    /// <typeparam name="T">The type of entry</typeparam>
    /// <param name="set">The database set</param>
    /// <param name="newList">The new list</param>
    /// <param name="orgList">The original list</param>
    public void AddOrUpdateCollection<T>(DbSet<T> set, ICollection<T> newList, ICollection<T> orgList) where T : class, IBase
    {
        // attach or update all entries in the new list
        foreach (T entry in newList)
        {
            // Find out if we had the entry already in the list
            var orgEntry = orgList.SingleOrDefault(e => e.Id != 0 && e.Id == entry.Id);

            AddOrUpdateEntry(set, entry, orgEntry);
        }

        // Remove all entries from the original list that are no longer in the new list
        foreach (T orgEntry in orgList.Where(e => e.Id != 0).ToList())
        {
            if (!newList.Any(e => e.Id == orgEntry.Id))
            {
                set.Remove(orgEntry);
            }
        }
    }

To use it i do the following:

var originalParent = _dbContext.ParentItems
    .Where(p => p.Id == parent.Id)
    .Include(p => p.ChildItems)
    .Include(p => p.ChildItems2)
    .SingleOrDefault();

// Add the parent (including collections) to the context or update it's values (except the collections)
originalParent = AddOrUpdateEntry(_dbContext.ParentItems, parent, originalParent);

// Update each collection
AddOrUpdateCollection(_dbContext.ChildItems, parent.ChildItems, orgiginalParent.ChildItems);
AddOrUpdateCollection(_dbContext.ChildItems2, parent.ChildItems2, orgiginalParent.ChildItems2);

Hope this helps

---

EXTRA: You could also make a seperate DbContextExtentions (or your own context inferface) class:

public static void DbContextExtentions {
    /// <summary>
    /// Check if orgEntry is set update it's values, otherwise add it
    /// </summary>
    /// <param name="_dbContext">The context object</param>
    /// <param name="set">The collection</param>
    /// <param name="entry">The entry</param>
    /// <param name="orgEntry">The original entry found in the database (can be <code>null</code> is this is a new entry)</param>
    /// <returns>The added or updated entry</returns>
    public static T AddOrUpdateEntry<T>(this DbContext _dbContext, DbSet<T> set, T entry, T orgEntry) where T : class, IBase
    {
        if (entry.IsNew || orgEntry == null) // New or not found in context
        {
            entry.Id = 0;
            return set.Add(entry);
        }
        else
        {
            _dbContext.Entry(orgEntry).CurrentValues.SetValues(entry);
            return orgEntry;
        }
    }

    /// <summary>
    /// check if each entry of the new list was in the orginal list, if found, update it, if not found add it
    /// all entries found in the orignal list that are not in the new list are removed
    /// </summary>
    /// <typeparam name="T">The type of entry</typeparam>
    /// <param name="_dbContext">The context object</param>
    /// <param name="set">The database set</param>
    /// <param name="newList">The new list</param>
    /// <param name="orgList">The original list</param>
    public static void AddOrUpdateCollection<T>(this DbContext _dbContext, DbSet<T> set, ICollection<T> newList, ICollection<T> orgList) where T : class, IBase
    {
        // attach or update all entries in the new list
        foreach (T entry in newList)
        {
            // Find out if we had the entry already in the list
            var orgEntry = orgList.SingleOrDefault(e => e.Id != 0 && e.Id == entry.Id);

            AddOrUpdateEntry(_dbContext, set, entry, orgEntry);
        }

        // Remove all entries from the original list that are no longer in the new list
        foreach (T orgEntry in orgList.Where(e => e.Id != 0).ToList())
        {
            if (!newList.Any(e => e.Id == orgEntry.Id))
            {
                set.Remove(orgEntry);
            }
        }
    }
}

and use it like:

var originalParent = _dbContext.ParentItems
    .Where(p => p.Id == parent.Id)
    .Include(p => p.ChildItems)
    .Include(p => p.ChildItems2)
    .SingleOrDefault();

// Add the parent (including collections) to the context or update it's values (except the collections)
originalParent = _dbContext.AddOrUpdateEntry(_dbContext.ParentItems, parent, originalParent);

// Update each collection
_dbContext.AddOrUpdateCollection(_dbContext.ChildItems, parent.ChildItems, orgiginalParent.ChildItems);
_dbContext.AddOrUpdateCollection(_dbContext.ChildItems2, parent.ChildItems2, orgiginalParent.ChildItems2);

Ashelyashen

You could also make a extention class for your context with these functions: – Ashelyashen

Answer 19

I was face same problem when I am going to delete my record than some issue was occur , for this issue solution is that when you are going to delete your record than you missing some thing before deleting header/master record you must write to code for delete its detail before header/Master I hope you issue will be resolve.

Heretofore

Answer 20

I had the same issue when I was trying to modify the scalar property of the targeted entity and realized I have accidentally referenced the target entity's parent:

entity.GetDbContextFromEntity().Entry(entity).Reference(i => i.ParentEntity).Query().Where(p => p.ID == 1).Load();

Just an advice by making sure the target entity does not reference any parent.

Myelencephalon

Answer 21

I've met this problem before several hours and try everything, but in my case the solution was diferent from the listed above.

If you use already retrieved entity from the database and try to modify it's childrens the error will occure, but if you get fresh copy of the entity from the database there should not be any problems. Do not use this:

 public void CheckUsersCount(CompanyProduct companyProduct) 
 {
     companyProduct.Name = "Test";
 }

Use this:

 public void CheckUsersCount(Guid companyProductId)
 {
      CompanyProduct companyProduct = CompanyProductManager.Get(companyProductId);
      companyProduct.Name = "Test";
 }

Ishii