Entity framework - Modify a list of children objects - entity-framework

When I have a parent Entity hold a list of other entity (one to many relationship), I modify this list then call function to save the parent Entity. With the entities has removed from this list, is that the framework will delete them from database? And also the new entity has added to the list will be added to database?
thank for your help!

Assuming you have one to many relationship between Parent and Child, i. e., Parent has ChildList and Child has Parent.
Looking at the cases. If Parent is in the entity context and you add an instance of Child to ChildList of Parent, and save the context, then Child will be added to the database.
Parent parent = new Parent() { Name = "parent1" };
provider.AddToParentSet(parent)
parent.ChildList.Add(new Child() { Name = "child1" });
parent.ChildList.Add(new Child() { Name = "child2" });
parent.ChildList.Add(new Child() { Name = "child3" });
provider.SaveChanges();
If you remove one of the Child from the ChildList of Parent, and save the context, then you will get an exception because of the foreign key constraint.
Parent parent = provider.ParentSet.FirstOrDefault();
parent.ChildList.Remove(parent.ChildList.FirstOrDefault());
provider.SaveChanges();
If you delete one of the Childs that belong to ChildList of Parent from the context and save the context, it will be successful, it will be removed from database.
provider.DeleteObject(parent.ChildList.FirstOrDefault());
provider.SaveChanges();
Above situations are valid for default configuration of an entity model. Entity Framework also provides many options, you can also decide how your entity context behaves.
You just need to try these and such situations on your own. It will be better I think.

Related

Error when saving ObjectContext after replacing Parent item and linking Child item to it

In my application, the interface allows the user to create and delete entities in an Entity Framework model. All changes are added to the ObjectContext, and saved only when the user selects "Save".
My question is best asked by means of the following simple example:
I have a Foreign Key relation between two entity types, which I will call Parent and Child here. The database, in SQLite, is declared as follows:
CREATE TABLE Parents (ID INTEGER PRIMARY KEY);
CREATE TABLE Children
(
ID INTEGER PRIMARY KEY,
ParentID INTEGER NOT NULL
CONSTRAINT FK_ChildrenToParents REFERENCES [Parents](ID)
ON DELETE CASCADE ON UPDATE CASCADE
)
I then build an Entity Framework model on that database, and execute the following actions against it (see code below):
Create a Parent
Save
Delete the Parent
Create a new Parent with the same ID number as the original
Create a Child and provide it with the new Parent's ID number
Save (Fails)
demoDBEntities entities = new demoDBEntities();
Parent originalParent = new Parent { ID = 1 };
entities.Parents.AddObject(originalParent);
entities.SaveChanges(); // First Save
entities.Parents.DeleteObject(originalParent);
Parent newParent = new Parent { ID = 1 };
entities.Parents.AddObject(newParent);
Child newChild = new Child { ID = 2, ParentID = 1 };
entities.Children.AddObject(newChild);
entities.SaveChanges(); // Second Save
I get the following error on the second call to SaveChanges():
"Unable to insert or update an entity because the principal end of the 'demoDBModel.FK_Children_0_0' relationship is deleted."
It seems the problem is that the Entity Framework links the new Child item to the originalParent item, which is then deleted and replaced by the newParent item. This might sound conceited, but happens quite naturally in my application.
Is there any way for me to work around this problem?
PS: I know it's bad practice to re-use ID numbers of DB entries - however, in my case the ID numbers are Asset numbers, which could theoretically be reused. That said, the above scenario typically happens if the client creates a faulty Parent, then deletes it, recreates it, and then creates the Child item.
Instead of setting the foreign key property ParentID you could try to set one of the navigation properties (you must have at least one) and use only one call to AddObject to add the complete object graph to the context:
Either:
//...
entities.Parents.DeleteObject(originalParent);
Child newChild = new Child { ID = 2 };
Parent newParent = new Parent { ID = 1, Children = new List<Child>{ newChild } };
entities.Parents.AddObject(newParent);
entities.SaveChanges();
Or:
//...
entities.Parents.DeleteObject(originalParent);
Parent newParent = new Parent { ID = 1 };
Child newChild = new Child { ID = 2, Parent = newParent };
entities.Children.AddObject(newChild);
entities.SaveChanges();

Entity Framework: DBContext: How to Detecting entity exists in Database

Given the following example:
public class Parent
{
public Guid ID {get;set;}
public string Name {get;set;}
public Child Child {get;set;}
}
public class Child
{
public Guid ID {get;set;}
public string Name {get;set;}
}
I want to save a Parent object instance, with a Child instance assigned to it. The fact here is: the given child object already exists in the Database,
Parent p = new Parent();
p.ID = Guid.NewGuid();
// Get the Child Object
Child c = GetTheChild(...);
p.Child = c;
SaveParent ( p );
in function Save Parent, the following code is implemented:
public void SaveParent ( Parent p )
{
using (MyContext context = new ClinicContext())
{
context.Parents.Add( P );
context.SaveChanges();
}
}
Now the problem comes: since the child in this example already exists in the database, but when adding the parent in the context DBSet, the entity c given also holds a entry state of "Added", guess what? DBContext tries to save another child record with a duplicated Key!
Any body know how to solve this? I am thinking whether there is a way to turn a Insert into Update if the Entity Framework can detect the records already exists in the database.
Thanks for your help.
If you add an entity all releated entity will be added. If you attach an entity all related entities will be attached. In your case you want to add the Parent entity and then attach the child entity. What you could also try would be to use foreign keys and add parent and just set the foreign key to the related child Id. This way you would not have to bring the entity to the client to create the relationship (you need to know the key of the related entity though).
How are you getting the child? The child should be attached to the same context you save the parent on.
My guess is your GetTheChild function uses a new context - which means when you return the child is detached and for all intents and purposes EF figures its been 'added'
As panel said you can just add a foreign key and just set the child's key instead of the child itself but there seems to be some design issues you should address.
I guess GetTheChild() will return a child from database. So, all you need to do is call ChangeObjectState method to mark the child as Unchanged before calling SaveChanges.
var osm = context.ObjectStateManager;
osm.ChangeObjectState(child, EntityState.Unchanged);

Adding entity in the domain service insert method

I have two entities, Parent and Child, at the client side i create Parent and then call context.submitChanges
At the server side in the InsertParent(Parent parent) i do:
InsertParent(Parent parent)
{
Child child = this.ObjectContext.Childs.CreateObject();
parent.child = child;
if ((parent.EntityState != EntityState.Detached))
{
this.ObjectContext.ObjectStateManager.ChangeObjectState(parent, EntityState.Added);
}
else
{
this.ObjectContext.Parents.AddObject(parent);
}
}
Now i'm having two problems.
Before the if else, Parent.id is 0 and after its still 0 but in the database its populated.
The other one is, Child gets saved but Child.ParentId is 0.
I'm not understanding why.
Whats the correct way to achieve this behaviour? should i call SaveChanges() on the context directly?
Check to make sure the StoreGeneratedPattern property on Parent.Id in your edmx is set to Identity. That should make sure it gets updated with the new value on inserts.
I'd also wrap this in a transaction so you can add your child after the parent id is set.
using(var scope = new TransactionScope()){
ObjectContext.Parents.AddObject(parent);
ObjectContext.SaveChanges(); //parent.id assigned
parent.child = ObjectContext.Child.CreateObject();
ObjectContext.SaveChanges();
scope.Complete(); // commit transaction
}
Yes you should use the SaveChanges() because that's what persist your data into the Database.
Very Easy Example
You also need to check the parents.Id column and childs Id column that they are set as identity and as primary keys, and the relations between the two tables.

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

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();
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.
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();
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();
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)
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.
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
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.
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.
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.
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.
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
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);
}
}
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.
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; }
}
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();
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
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; }
}
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);
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.
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.
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";
}

Convince entity context (EF1) to populate entity references

I have an entity with self reference (generated by Entity Designer):
public MyEntity: EntityObject
{
// only relevant stuff here
public int Id { get...; set...; }
public MyEntity Parent { get...; set...; }
public EntityCollection<MyEntity> Children { get...; set...; }
...
}
I've written a stored procedure that returns a subtree of nodes (not just immediate children) from the table and returns a list of MyEntity objects. I'm using a stored proc to avoid lazy loading of an arbitrary deep tree. This way I get relevant subtree nodes back from the DB in a single call.
List<MyEntity> nodes = context.GetSubtree(rootId).ToList();
All fine. But when I check nodes[0].Children, its Count equals to 0. But if I debug and check context.MyEntities.Results view, Children enumerations get populated. Checking my result reveals children under my node[0].
How can I programaticaly force my entity context to do in-memory magic and put correct references on Parent and Children properties?
UPDATE 1
I've tried calling
context.Refresh(ClientWins, nodes);
after my GetSubtree() call which does set relations properly, but fetches same nodes again from the DB. It's still just a workaround. But better than getting the whole set with context.MyEntities().ToList().
UPDATE 2
I've reliably solved this by using EF Extensions project. Check my answer below.
You need to assign one end of the relationship. First, divide the collection:
var root = nodes.Where(n => n.Id == rootId).First();
var children = nodes.Where(n => n.Id != rootId);
Now, fix up the relationship.
In your case, you'd do either:
foreach (var c in children)
{
c.Parent = root;
}
...or:
foreach (var c in children)
{
root.Children.Add(c);
}
It doesn't matter which.
Note that this marks the entities as modfied. You'll need to change that if you intend to call SaveChanges on the context and don't want this saved.
The REAL solution
Based on this article (read text under The problem), navigation properties are obviously not populated/updated when one uses stored procedures to return data.
But there's a nice manual solution to this. Use EF Extensions project and write your own entity Materilizer<EntityType> where you can correctly set navigation properties like this:
...
ParentReference = {
EntityKey = new EntityKey(
"EntityContextName.ParentEntitySetname",
new[] {
new EntityKeyMember(
"ParentEntityIdPropertyName",
reader.Field<int>("FKNameFromSP")
)
})
}
...
And that's it. Calling stored procedure will return correct data, and entity object instances will be correctly related to eachother. I advise you check EF Extensions' samples, where you will find lots of nice things.