Question

i have a view that shows the user a form and the user should upload a file and choose all the categories associated with it.

the controller that is responsible in submitting the data should

• retrieve the file info and
  insert data in the file category

• retrieve the related category ids and
  insert them as well in the table
  that is abstracted by the EF just
  insert the file and the category ids.

this is my problem the controller just gets some info about the category not all of it. basically it only needs the ids for the insertion

i can’t use

        [HttpPost]
    public ActionResult SaveFile(File file, List<Category> Checkbox, HttpPostedFileBase FileUpload)
    {
        //some stuff
        //for example got the first category and named it to category1
        file.Categories.Add(category1)
    }

i asked someone and he told me you have to select the category you want to insert

is this really necessary ? i only need a category id and a file id to make the insert why would i fire another request to the database that i don’t really need

---

i am using

• EF 4
• MVC 3

Answer 1

It is better to select category first because it will save you a lot of possible problems but it is not necessary. You can use dummy category object:

  var category = new Category { Id = receivedId };
  file.Categories.Add(category);

You will only create new category and you will set its PK. Now you need to handle file insertion where you must explicitly instruct ObjectContext to insert only file (because your categories exists in database):

context.Files.Attach(file); // now whole object graph is attached but marked as Unchanged
context.ObjectStateManager.ChangeObjectState(file, EntityState.Added); // mark only file entity as inserted
context.SaveChanges();

You can also take opposite direction:

context.Files.AddObject(file); // all objects in object graph are marked for insertion
foreach (var category in file.Categories)
{
  // you don't want to insert categories again
  context.ObjectStateManager.ChangeObjectState(category, EntityState.Unchanged); 
}
context.SaveChanges();

This scenario works if you know that all categories exist in your database. If you want to insert new categories together with saving file you will need to query categories first or add some information about which category is new and which is existing.