Question

This is driving me nuts. I’m not sure what else to try. This is my latest attempt to update a list of objects within another object using EF 4.3.

The scenario is that a user has added a new Task to an Application that already has one task in its Tasks property. The Application is not attached to the DB context because it was retrieved in a prior logic/DB call. This is the class and property:

public class Application : EntityBase
{
    public ObservableCollection<TaskBase> Tasks { // typical get/set code here }
}

This is my attempt to update the list. What happens is that the new Task gets added and the association correctly exists in the DB. However, the first task, that wasn’t altered, has its association removed in the DB (its reference to the Application).

This is the Save() method that takes the Application that the user modified:

public void Save(Application newApp)
{
    Application appFromContext;

    appFromContext = this.Database.Applications
        .Include(x => x.Tasks)
        .Single(x => x.IdForEf == newApp.IdForEf);

    AddTasksToApp(newApp, appFromContext);
    this.Database.SaveChanges();
}

And this is the hooey that’s apparently necessary to save using EF:

private void AddTasksToApp(Application appNotAssociatedWithContext, Application appFromContext)
{
    List<TaskBase> originalTasks = appFromContext.Tasks.ToList();

    appFromContext.Tasks.Clear();

    foreach (TaskBase taskModified in appNotAssociatedWithContext.Tasks)
    {
        if (taskModified.IdForEf == 0)
        {
            appFromContext.Tasks.Add(taskModified);
        }
        else
        {
            TaskBase taskBase = originalTasks.Single(x => x.IdForEf == taskModified.IdForEf);  // Get original task
            this.Database.Entry(taskBase).CurrentValues.SetValues(taskModified);  // Update with new
        }
    }
}

Can anyone see why the first task would be losing its association to the Application in the DB? That first task goes through the else block in the above code.

Next, I’ll need to figure out how to delete one or more items, but first things first…

Answer 1

After continual trial and error, this appears to be working, including deleting Tasks. I thought I’d post this in case it helps someone else. I’m also hoping that someone tells me that I’m making this more complicated than it should be. This is tedious and error-prone code to write when saving every object that has a list property.

private void AddTasksToApp(Application appNotAssociatedWithContext, Application appFromContext)
{
    foreach (TaskBase taskModified in appNotAssociatedWithContext.Tasks)
    {
        if (taskModified.IdForEf == 0)
        {
            appFromContext.Tasks.Add(taskModified);
        }
        else
        {
            TaskBase taskBase = appFromContext.Tasks.Single(x => x.IdForEf == taskModified.IdForEf);  // Get original task
            this.Database.Entry(taskBase).CurrentValues.SetValues(taskModified);  // Update with new
        }
    }

    // Delete tasks that no longer exist within the app.
    List<TaskBase> tasksToDelete = new List<TaskBase>();
    foreach (TaskBase originalTask in appFromContext.Tasks)
    {
        TaskBase task = appNotAssociatedWithContext.Tasks.Where(x => x.IdForEf == originalTask.IdForEf).FirstOrDefault();

        if (task == null)
        {                    
            tasksToDelete.Add(originalTask);
        }
    }

    foreach (TaskBase taskToDelete in tasksToDelete)
    {                
        appFromContext.Tasks.Remove(taskToDelete);
        this.Database.TaskBases.Remove(taskToDelete);
    }
}