I am working on Entity Framework 4.0 . Here Adding control into database using AddObject() and save that suing SaveChange() methods.
But once I delete that added control and try to add again same I am getting this error again and again
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.
I am not able to add it. Once I close my application then try to add then I am able to add that control.
I tried to search a lot here and there how it going wrong but could not find solution.
As I am new born in field in Entity Framework.
public void Add(SearchPath entity) {
_context.SearchPaths.AddObject(entity);
// _context.Save(entity, false);
}
public void Remove(SearchPath entity)
{
if (entity.Path != null)
{
using (EntityContext entityObj = new EntityContext())
{
entityObj.SearchPaths.Attach(entity);
entityObj.SearchPaths.DeleteObject(entity);
entityObj.SaveChanges();
}
}
}
public void Modify(SearchPath entity)
{
using (EntityContext entityObj = new EntityContext())
{
try
{
entityObj.SearchPaths.Attach(entity);
entityObj.ObjectStateManager.ChangeObjectState(entity, System.Data.EntityState.Modified);
entityObj.SaveChanges();
}
catch (OptimisticConcurrencyException)
{
entityObj.Refresh(RefreshMode.StoreWins, entity);
entityObj.SaveChanges();
}
}
}
public void Add(Package entity)
{
_context.Packages.AddObject(entity);
}
public void Remove(Package entity)
{
if (_context.GetEntityState(entity) == EntityState.Unchanged)
_context.Packages.Attach(entity);
_context.Packages.DeleteObject(entity);
}
Answer for above problem is Just call your own save method like this.
public void Save(object entity)
{
using (var transaction = Connection.BeginTransaction())
{
try
{
SaveChanges();
transaction.Commit();
}
catch (OptimisticConcurrencyException)
{
if (ObjectStateManager.GetObjectStateEntry(entity).State == EntityState.Deleted || ObjectStateManager.GetObjectStateEntry(entity).State == EntityState.Modified)
this.Refresh(RefreshMode.StoreWins, entity);
else if (ObjectStateManager.GetObjectStateEntry(entity).State == EntityState.Added)
Detach(entity);
AcceptAllChanges();
transaction.Commit();
}
}
}
once I delete that added control and try to add again
The problem is that you apparently do that in the same context. To me that indicates that the context's lifespan is too long. The best way to use context instances in EF is one context per unit of work (or business transaction, or use case).
So if you want to delete a control: create a context, delete the the control, dispose the context. If you want to add it again (for some reason): create a context, add the control, dispose the context. From your code snippets it is not entirely clear to me if this happens in your code.
Related
I have the following code:
Get contact
public Contact LoadContactFromId(int contactId)
{
using(var ctx = new ContactContext())
{
var contact = ctx.Contacts.AsNoTracking().First(c => c.ContactId == contactId);
return contact;
}
}
Update Contact
public void UpdateExistingContact(Contact updatedContact)
{
using(var ctx = new ContactContext())
{
ctx.Contacts.Attach(updatedContact);
ctx.Entry(updatedContact).State = EntityState.Modified;
foreach (var item in updatedContact.ContactPoints)
{
ctx.Entry(item).State = (item.ContactPointId == 0) ? EntityState.Added : EntityState.Modified;
}
ctx.SaveChanges();
}
}
I am currently working with ASP.NET webforms and because of its stateless model, I can't keep working within the DbContext. Because of this, I end up basically recreating the entire Contact entity from the POST data and then update it.
This seems like a horrible way to do this because I lose conncurrncey resolution since I'm not working with the true original entity and it seems kind of cumbersome to always have to recreate the object.
Is there an easier way to do this? Am I looking at this all wrong?
I'm using EF5 with MVC and POCO's and need a little help
I have an update function which is passed a disconnected POCO. The POCO has a 'navigation property' collection, eg: Provider has
public virtual ICollection<Company> Companies { get; set; }
When the Provider was loaded (and the old context closed) it had two Company objects, now it has four and I'd like to update.
I thought the code below might work but Companies is not updated (but the non-navigational properties of Provider (like string Name {get;set} are still updated ok) and there is no error
public void Update(Provider entity)
{
// Existing entity
_context.Entry(entity).State = EntityState.Modified;
if (entity.Companies.Any())
{
//try to tell EF about the companies
foreach (var company in entity.Companies)
{
//the company exists already - let the context know....
_context.Entry(company).State = EntityState.Modified;
_context.Companies.Attach(company);
}
}
}
... and later: _unitOfWork.SaveChanges();
For an insert of Provider with Companies I had successfully used:
if (entity.Companies.Any())
{
//these are not to be created - they exist -
//I want EF to add them as nav properties
foreach (var company in entity.Companies)
{
//the company exists already - let the context know....
_pvpContext.Companies.Attach(company);
}
}
// New entity
_pvpContext.Entry(entity).State = EntityState.Added;
I'm going to go and read Julia Lerman's book as EF is killing me - but I'd really appreciate any help updating 'Companies' in the meantime - Thx
Edit:
Taking #Manos' kind advice I tried:
List<Company> companies = new List<Company>();
if (entity.Companies != null && entity.Companies.Any())
{
//pull out the Companies from the POCO
companies = entity.Companies.ToList();
//remove them
entity.Companies = new Collection<Company>();
entity.Companies.Clear();
}
// pass existing entity to the context, tagged as modified
_pvpContext.Entry(entity).State = EntityState.Modified;
if (companies.Any())
{
//now re-add the companies while the context is listening. ffs.
foreach (var company in companies)
{
entity.Companies.Add(company);
}
}
If I add the Provider.Companies to the context (like in the insert) I get:
Violation of PRIMARY KEY constraint 'PK__tmp_ms_x__679519B7F943FD8D'.
Cannot insert duplicate key in object 'dbo.ProviderCompany'. The
duplicate key value is (5, 3)
which is odd as there is not composite key of (provider 5, company 3) - so maybe it's trying to add it in twice here?
If I don't pre-add the Provider.Companies I get:
at System.Data.Entity.Internal.InternalContext.SaveChanges() at
System.Data.Entity.Internal.LazyInternalContext.SaveChanges() at
System.Data.Entity.DbContext.SaveChanges()
I only have 4.1 to test, but try this as a basic logic:
public void Update(Provider entity)
{
// Existing entity
Provider contextProvider = _context.Entry(entity);
contextProvider.Companies.Clear();
foreach (var company in entity.Companies)
{
contextProvider.Companies.Add(company);
}
}
This needs a little refinement in order to only add new companies as opposed to doing a complete removal and reinstatement but it should work.
Edit in response to comment:
Try catching the exception thrown by SaveChanges() with the following:
try {
_unitOfWork.SaveChanges();
} catch (System.Data.Entity.Validation.DbEntityValidationException e) {
foreach (var k in e.EntityValidationErrors) {
foreach (var e1 in k.ValidationErrors) {
Console.WriteLine("{0} - {1}", e1.PropertyName, e1.ErrorMessage);
}
}
}
It should give you a little more information to go on.
I'm writing a DAL class using EF4.0, I've read
http://www.codeproject.com/Articles/43367/ADO-NET-Entity-Framework-as-Data-Access-Layer
and
http://msdn.microsoft.com/en-us/magazine/cc700340.aspx
But when I test their code, I meet some problem with the Update and Delete method.
The DAL class all code is below:
public class FriendlinkDA : IDisposable
{
private EdiBlogEntities context;
public FriendlinkDA()
{
context = new EdiBlogEntities();
}
public void Dispose()
{
context.Dispose();
}
public FriendLink GetFriendLink(Guid id)
{
return context.FriendLink.FirstOrDefault(f => f.Id == id);
}
public void Update(FriendLink model)
{
// Way 1: (throw exception)
//context.Attach(model);
//model.SetAllModified(context);
//context.SaveChanges();
// Way 2:
EntityKey key;
object originalItem;
key = context.CreateEntityKey("FriendLink", model);
if (context.TryGetObjectByKey(key, out originalItem))
{
context.ApplyCurrentValues(key.EntitySetName, model);
//context.ApplyPropertyChanges(key.EntitySetName, model);
}
context.SaveChanges();
}
public void Delete(FriendLink model)
{
// Way 1:
context.Attach(model);
context.DeleteObject(model);
context.SaveChanges();
// Way 2:
//var item = context.FriendLink.FirstOrDefault(f => f.Id == model.Id);
//context.DeleteObject(item);
//context.SaveChanges();
}
}
The extension method is:
public static void SetAllModified<T>(this T entity, ObjectContext context) where T : IEntityWithKey
{
var stateEntry = context.ObjectStateManager.GetObjectStateEntry(entity.EntityKey);
var propertyNameList = stateEntry.CurrentValues.DataRecordInfo.FieldMetadata.Select
(pn => pn.FieldType.Name);
foreach (var propName in propertyNameList)
stateEntry.SetModifiedProperty(propName);
}
In the application, I am use the DAL like this:
// Delete
using (var optFriendlink = new FriendlinkDA())
{
var test = optFriendlink.GetFriendLink(new Guid("81F58198-D396-41DE-A240-FC306C7343E8"));
optFriendlink.Delete(test);
}
// Update
using (var optFriendlink = new FriendlinkDA())
{
var testLink = optFriendlink.GetFriendLink(new Guid("62FD0ACF-40C3-4BAD-B438-38BB540A6080"));
testLink.Title = "ABC";
optFriendlink.Update(testLink);
}
Question 1:
In Delete(), both way 1 and way 2 can work. Which one is better?
Question 2:
In Update(), way 1 give me an exception: The object cannot be attached because it is already in the object context. An object can only be reattached when it is in an unchanged state.
on this statment: context.Attach(model);
but way 2 is fine.
why is this happening? I also attach the model in Delete(), why Delete() is working fine? how I can write the update correctly?
The exception says it all:
An object can only be reattached when it is in an unchanged state.
You change the object in the code snippet under // Update, so that's why it cannot be re-attached.
As to which method is better. Normally you would get an object from a context, dispose of the context, do something with the object and then use a new context to save the object. In that case using Attach is much more comfortable then getting an object by Id first.
I have seen many examples using Entity Framework in MVC3 applications, they are very simple demos which only have one mvc3 web project with edmx inside it.
So, they can use the best practice for open and close connection by "using" statement:
using(var context = new SchoolEntities())
{
// do some query and return View with result.
}
And, It can use lazy load (navigation properties) inside the "using" statment correctly, because the context is not yet
disposed:
foreach(var item in student.Course)
{
// do something with the navigation property Course
}
All things seems to be perfect until it becomes an n-tier application.
I created DAL, BLL, and a MVC3 UI.
The DAL have edmx inside it, and operator classes like SchoolDA.cs:
public class StudentDA()
{
public Student FindStudent(int studentId)
{
using(var context = new SchoolContext())
{
// do query, return a student object.
}
}
}
Then, in the BLL, if I use:
var student = studentDa.FindStudent(103);
then invoke it's navigation property:
student.Course
I will get an error (of course):
The ObjectContext instance has been disposed and can no longer be used for operations that require a connection.
So, I have to change StudentDA.cs like this:
public class StudentDA() : IDisposable
{
private SchoolEntites context;
public StudentDA()
{
context = new SchoolEntities();
}
public void Dispose()
{
context.Dispose();
}
public Student FindStudent(int studentId)
{
// do query, return a student object.
}
}
Then, the BLL will change like this:
public Student FindStudent(int id)
{
using(var studentDa = new StudentDA())
{
// this can access navigation properties without error, and close the connection correctly.
return studentDa.FindStudent(id);
}
}
All things seem to be perfect again until it meet Update() method.
Now, if I want to update a student object which is taken from BLL.FindStudent(), the context.SaveChanges() will return 0, because the context is already disposed in the BLL.FindStudent(), and nothing will be updated to database.
var optStudent = new StudentBO();
var student = optStudent.FindStudent(103);
student.Name = "NewValue";
optStudent.Update(student);
Does anyone have idea on how to use EntityFramework in 3 tire application? or how can I manage the context correctly. I will use navigation propertites very often in the web layer, but I can't always remain connection open to consume the server memory.
There are multiple ways to handle EF context's lifetime. In web apps, usually context is unique for an HttpRequest. For example, if you want to handle this manually in a web application and have a per Thread/HttpRequest EF context, you can do so with the following (Code copied from http://www.west-wind.com/weblog/posts/2008/Feb/05/Linq-to-SQL-DataContext-Lifetime-Management):
internal static class DbContextManager
{
public static DbContext Current
{
get
{
var key = "MyDb_" + HttpContext.Current.GetHashCode().ToString("x")
+ Thread.CurrentContext.ContextID.ToString();
var context = HttpContext.Current.Items[key] as MyDbContext;
if (context == null)
{
context = new MyDbContext();
HttpContext.Current.Items[key] = context;
}
return context;
}
}
}
And then you can easily use:
var ctx = DbContextManager.Current
But I suggest you leave the lifetime management to an IoC framework like Autofac, Castle Windsor, or Ninject which automatically handle the creation/disposal of your registered obejcts along with many other features.
Thanks for your answer Kamyar. I came across this whilst looking for a simple strategy to manage the ObjectContext lifetime without having to use an IoC framework, which seems a bit overkill for my needs.
I also came across your other post here, for disposing of the context at the end of the request.
Thought this might be useful for others coming across this, so just posting my implementation of your code here:
Context manager class -
internal static class MyDBContextManager
{
//Unique context key per request and thread
private static string Key
{
get
{
return string.Format("MyDb_{0}{1}", arg0: HttpContext.Current.GetHashCode().ToString("x"),
arg1: Thread.CurrentContext.ContextID);
}
}
//Get and set request context
private static MyDBContext Context
{
get { return HttpContext.Current.Items[Key] as MyDBContext; }
set { HttpContext.Current.Items[Key] = value; }
}
//Context per request
public static MyDBContext Current
{
get
{
//if null, create new context
if (Context == null)
{
Context = new MyDBContext();
HttpContext.Current.Items[Key] = Context;
}
return Context;
}
}
//Dispose any created context at the end of a request - called from Global.asax
public static void Dispose()
{
if (Context != null)
{
Context.Dispose();
}
}
}
Global.asax (MVC) -
public override void Init()
{
base.Init();
EndRequest +=MvcApplication_EndRequest;
}
private void MvcApplication_EndRequest(object sender, EventArgs e)
{
MyDBContextManager.Dispose();
}
I try to do the following with entity framework 4 :
public void Update(Site entity)
{
using (db)
{
db.Sites.Attach(db.Sites.Single(s => s.Id == entity.Id));
db.Sites.ApplyCurrentValues(entity);
db.SaveChanges();
}
}
But when i try to update a site through this method i get an error telling me that :
The conversion of a datetime2 data
type to a datetime data type resulted
in an out-of-range value. The
statement has been terminated.
And this is because the original site for some reason is not loaded through the Attach() method.
Can someone help with this ?
/Martin
You don't need to "attach" something you are already retrieving (Ladislav is right). Once you retrieve an entity (e.g SingleOrDefault), it is "in the graph" (EF memory - so it can do optimistic concurrency).
If your trying to do an UPDATE< and the "entity" your passing through is new/detached...
Try the stub technique:
public void Update(Site entity)
{
using (db)
{
var stub = new Site { Id = entity.Id }; // create stub with given key
db.Sites.Attach(stub); // stub is now in graph
db.Sites.ApplyCurrentValues(entity); // override graph (stub) with entity
db.SaveChanges();
}
}
That being said, the error you have provided points to some other issue (data conversion).
Have you checked the "date" values you are passing through with the data type on the model?
public ActionResult Edit(int id, Client collection)
{
try
{
// make sure the rec is in the context
var rec = dbEntities.Clients.First(r => r.ClientID == id);
// update the rec in the context with the parm values
dbEntities.Clients.ApplyCurrentValues(collection);
// make the changes permanent
dbEntities.SaveChanges();
return RedirectToAction("Index");
}
catch
{
return View();
}
}