Develop Reference

EF code first update entity with its children

I got update method that updates only the entity without its children
public void Update(T obj)
{
Ensure.IsNull(obj);
using (var DB = AccessManager.db)
{
DB.Set<T>().Attach(obj);
DB.Entry(obj).State = System.Data.EntityState.Modified;
DB.SaveChanges();
}
}
I try to update
LessonModel.Title = "Updated";
LessonModel.Files.Add(new LessonFileModel { IdxNumber = LessonModel.IdxNumber, FileName = "asd", FilePath = " asdf" });
DALFacade.Lesson.Update(LessonModel);
Only the title gets updated. The files are not updated.
So if the method like this:
public void Update(LessonModel obj)
{
Ensure.IsNull(obj);
using (var DB = AccessManager.db)
{
DB.Lessons.Attach(obj);
DB.Entry(obj).State = System.Data.EntityState.Modified;
DB.SaveChanges();
}
}
How can i save the child?

This is one of the problems that arise when you use the "Generic Repository" anti pattern. Writing an Update method that works for every combination of entity graphs that you pass in and will always do exactly what you want it to do is a big pain in the EF.
Instead, try writing repositories that match your use cases.
Your current problem could be solved if you added the files to the lesson after you attached it to the context. Marking an entry as modified marks all properties on this entry as modified, it doesn't affect relationships.

Entity Framework 5.0 db.savechange not working

When I try to update my entry in update function it's execute successfully but database not updated.
Please find the following code
public static string UpdateEmployee(Employee employee)
{
using (var db = new RandDEntities())
{
var empObj = db.Employees.First(x => x.EmpID == employee.EmpID);
db.Entry(empObj).State = EntityState.Modified;
db.SaveChanges();
}
return "";
}

The problem is that you're saving the wrong entity (i.e. empObj) instead of the entity that has the changes (i.e. employee). Your code pulls empObj out of the database, and then turns around and saves it, without making any changes to it. You need to modify your code as follows:
public static string UpdateEmployee(Employee employee)
{
using (var db = new RandDEntities())
{
db.Employees.Attach(employee);
db.Entry(employee).State = EntityState.Modified;
db.SaveChanges();
}
return "";
}

That has absolutely nothing to do with Entity Framework but more with the fact that you likely use localdb and your database is not where you think it is, and reinitialized (reset) to empty every time you press start.
This question, in dozens of variants, gets asked over and overy by people not bothering to check where they look (and then realizing the database files have different paths).

C# entity framework 5 set a property only in create

I have a model with a property called "datetime_inclusion" and I need to set a value for this ONLY when I save the first time, there is a way to do this treatment in the model?
I use C# MVC5 and entity framework 5

When you save the first time your object won't have an ID until it gets put into the DB. You can check against this to set your value.
if(myEntity.ObjectID <= 0)
{
myEntity.DateAdded = DateTime.Now;
}

Shoe's answer is perfect. But if you are worry that property can be change in edit time, control that. In create action use Shoe's code and in Edit action use:
[HttpPost]
public ActionResult Edit(int id, Model model)
{
using (var db = new YourEntities())
{
//control that, it does not change
model.datetime_inclusion = db.YourTable.Find(id).datetime_inclusion;
db.Entry(model).State = System.Data.EntityState.Modified;
db.SaveChanges();
return RedirectToAction("Index");
}
}

Multiple instances of IEntityChangeTracker Error

I've read through at least a dozen other questions just like this one, but I am having trouble grasping some of this stuff.
I'm used to developing ASP.NET MVC3 with repositories and code-first entities linking to the entity framework.
I've recently switched to database-first ADO.NET with services development.
I find this to be very clean since I can access stuff through my foreign keys.
Anyway, my old save methods seem to be broken since I constantly get this error
An entity object cannot be referenced by multiple instances of
IEntityChangeTracker
So here's a look at my save action and my service:
Action:
[HttpPost]
public ActionResult AddReview(Review review, int id)
{
User loggedInUser = userService.GetUserByusername(User.Identity.Name);
review.WriterId = loggedInUser.UserId;
review.ProductId = id;
if (ModelState.IsValid)
{
reviewService.Save(review);
Product product = productService.GetProduct(id);
if(product.Quantity>=1)
product.Quantity--;
product.TimesBought++;
productService.UpdateRating(product, reviewService);
loggedInUser.GoldCoins -= product.Price;
Session["goldCoins"] = loggedInUser.GoldCoins;
userService.Save(loggedInUser);
productService.Save(product);
}
else
{
return View(review);
}
return RedirectToAction("Index", "Answers", new { reviewId = review.ReviewId });
Service:
public class ReviewService : Service<Review, CapstoneEntities>
{
...
public void Save(Review review)
{
using (var db = new CapstoneEntities())
{
if (review.ReviewId == 0)
{
db.Reviews.Add(review);
db.Entry(review).State = EntityState.Added;
}
else
{
db.Entry(review).State = EntityState.Modified;
}
db.SaveChanges();
}
}
}
My suspicion is with this line of code: using (var db = new CapstoneEntities()) but I'm not sure how else to do this. Again, this worked perfectly with my old way of doing things but now I get errors on just about ever CRUD operation.
Thank you.

It looks like this is being caused by having an entity belong to multiple DataContexts. Whatever code that is calling that action should use the same DataContext to create the entity as the one used to persist it to the datastore.
In most instances you should only keep one instance of the DataContext. You can use a DI framework like Castle to define/store a dependency (in this case the DataContext) as Transient or PerWebRequest and inject it into the service and controller, so you'll always have a reference to the same instance of the DataContext.

I am new to MVC & Entity frame work. I got same problem after fighting a lot
This solution worked for me. Hope it can be useful for you guys.
var mediaItem = db.MediaItems.FirstOrDefault(x => x.Id == mediaItemViewModel.Id);
mediaItem.Name = mediaItemViewModel.Name;
mediaItem.Description = mediaItemViewModel.Description;
mediaItem.ModifiedDate = DateTime.Now;
mediaItem.FileName = mediaItem.FileName;
mediaItem.Size = KBToMBConversion(mediaItemViewModel.Size);
mediaItem.Type = mediaItem.Type;
//db.Entry(mediaItem).State = EntityState.Modified;// coment This line
db.SaveChanges();
Cause you are reading the the whole object from db and holding it in the current context and when you try to modify the entity state its tells you already one entity attached to the current context. just call save changes it will save it.

Implementing Audit Log / Change History with MVC & Entity Framework

I am building in a Change History / Audit Log to my MVC app which is using the Entity Framework.
So specifically in the edit method public ActionResult Edit(ViewModel vm), we find the object we are trying to update, and then use TryUpdateModel(object) to transpose the values from the form on to the object that we are trying to update.
I want to log a change when any field of that object changes. So basically what I need is a copy of the object before it is edited and then compare it after the TryUpdateModel(object) has done its work. i.e.
[HttpPost]
public ActionResult Edit(ViewModel vm)
{
//Need to take the copy here
var object = EntityFramework.Object.Single(x=>x.ID = vm.ID);
if (ModelState.IsValid)
{
//Form the un edited view model
var uneditedVM = BuildViewModel(vm.ID); //this line seems to confuse the EntityFramework (BuildViewModel() is used to build the model when originally displaying the form)
//Compare with old view model
WriteChanges(uneditedVM, vm);
...
TryUpdateModel(object);
}
...
}
But the problem is when the code retrieves the "unedited vm", this is causing some unexpected changes in the EntityFramework - so that TryUpdateModel(object); throws an UpdateException.
So the question is - in this situation - how do I create a copy of the object outside of EntityFramework to compare for change/audit history, so that it does not affect or change the
EntityFramework at all
edit: Do not want to use triggers. Need to log the username who did it.
edit1: Using EFv4, not too sure how to go about overriding SaveChanges() but it may be an option
This route seems to be going nowhere, for such a simple requirement! I finally got it to override properly, but now I get an exception with that code:
public partial class Entities
{
public override int SaveChanges(SaveOptions options)
{
DetectChanges();
var modifiedEntities = ObjectStateManager.GetObjectStateEntries(EntityState.Modified);
foreach (var entry in modifiedEntities)
{
var modifiedProps = ObjectStateManager.GetObjectStateEntry(entry).GetModifiedProperties(); //This line throws exception The ObjectStateManager does not contain an ObjectStateEntry with a reference to an object of type 'System.Data.Objects.EntityEntry'.
var currentValues = ObjectStateManager.GetObjectStateEntry(entry).CurrentValues;
foreach (var propName in modifiedProps)
{
var newValue = currentValues[propName];
//log changes
}
}
//return base.SaveChanges();
return base.SaveChanges(options);
}
}

IF you are using EF 4 you can subscribe to the SavingChanges event.
Since Entities is a partial class you can add additional functionality in a separate file. So create a new file named Entities and there implement the partial method OnContextCreated to hook up the event
public partial class Entities
{
partial void OnContextCreated()
{
SavingChanges += OnSavingChanges;
}
void OnSavingChanges(object sender, EventArgs e)
{
var modifiedEntities = ObjectStateManager.GetObjectStateEntries(EntityState.Modified);
foreach (var entry in modifiedEntities)
{
var modifiedProps = ObjectStateManager.GetObjectStateEntry(entry.EntityKey).GetModifiedProperties();
var currentValues = ObjectStateManager.GetObjectStateEntry(entry.EntityKey).CurrentValues;
foreach (var propName in modifiedProps)
{
var newValue = currentValues[propName];
//log changes
}
}
}
}
If you are using EF 4.1 you can go through this article to extract changes

See FrameLog, an Entity Framework logging library that I wrote for this purpose. It is open-source, including for commercial use.
I know that you would rather just see a code snippet showing how to do this, but to properly handle all the cases for logging, including relationship changes and many-to-many changes, the code gets quite large. Hopefully the library will be a good fit for your needs, but if not you can freely adapt the code.
FrameLog can log changes to all scalar and navigation properties, and also allows you to specify a subset that you are interested in logging.

There is an article with high rating here at the codeproject: Implementing Audit Trail using Entity Framework . It seems to do what you want. I have started to use this solution in a project. I first wrote triggers in T-SQL in the database but it was too hard to maintain them with changes in the object model happening all the time.