Unable to update child entity using Entity Framework

Question

These are my model classes.

public class Survey
{
    [Key]
    public int SurveyID { get; set; }
    [Required]
    public string Title { get; set; }
    [DataType(DataType.Text)]
    [Required]
    public string Description { get; set; }
    public virtual Category Category { get; set; }
}

public class Category
{
    [Key]
    public int CategoryID { get; set; }
    public string CategoryText { get; set; }
}

In the edit action of the SurveyController the survey properties are updating but not the category.

Here is the edit action code.

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Edit(Survey survey)
{
    db.Database.Log = s => Debug.WriteLine(s);

    if (ModelState.IsValid)
    {
        db.Entry(survey).State = EntityState.Modified;
        db.SaveChanges();
        return RedirectToAction("Index");
    }

    return View(survey);
}

try to mark the child state as modified explicitly.

Amit Kumar Ghosh
– Amit Kumar Ghosh

2015-12-10 10:45:13 +00:00
Commented Dec 10, 2015 at 10:45 — Amit Kumar Ghosh
– Amit Kumar Ghosh, Commented Dec 10, 2015 at 10:45
stackoverflow.com/questions/18054798/…

Amit Kumar Ghosh
– Amit Kumar Ghosh

2015-12-10 10:45:22 +00:00
Commented Dec 10, 2015 at 10:45 — Amit Kumar Ghosh
– Amit Kumar Ghosh, Commented Dec 10, 2015 at 10:45
Tried it.. doesn't work

Rahul Shinde
– Rahul Shinde

2015-12-10 10:58:59 +00:00
Commented Dec 10, 2015 at 10:58 — Rahul Shinde
– Rahul Shinde, Commented Dec 10, 2015 at 10:58

Navoneel Talukdar · Accepted Answer · 2015-12-10 11:19:24Z

3

Entity framework by default does not update the navigation properties. EF only knows/tracks the changes in the properties you explicitly update. EF can only save child objects if the parent object is retrieved with the same context.

As a solution you need to explicitly iterate over your child properties and set its state to modified.

Sample code

 foreach (var childModel in model.Children)
    {
        var existingChild = existingParent.Children
            .Where(c => c.Id == childModel.Id)
            .SingleOrDefault();

        if (existingChild != null)
           _dbContext.Entry(existingChild).CurrentValues.SetValues(childModel);
    }

Update

var child = new ChildEntity() {Id = 1};
child.ParentEntityId = 1;  // Assigning FK
context.Childs.Attach(child);
context.Entry(child).State = EntityState.Modified;
context.SaveChanges();

edited Dec 10, 2015 at 11:19

answered Dec 10, 2015 at 10:51

Navoneel Talukdar

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1 Comment

Rahul Shinde Over a year ago

I just want to update the foreign key of the survey entity

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