asp.net mvc: binding complex objects

Question

1. consider classic example: Product and Category
2. editing Product
3. in dropdown Id of Category is selected - Category mapped as object with all fields empty except Id
4. when submitting Product edit form - validation gives an error: "Category name is required" (I have Required attribute on Category Name property)

How deal with such errors if I want to use built-in validation (if (!ModelState.IsValid))? Writing custom data binder which would fill all such id-only-objects with values from database comes to mind.

Do you have any other solutions for this problem?

Answer 1

Hi,

You need to pass back your edited product and the category id. Then in you controller/repository get the category from the passed category id and set the category as the product category.

As the category is returned from the db (or wherever) all the properties should be propulates so you shouldn't get "Category name is required"

A quick example of what I mean:

[HTTPost]
public ActionResult Save(Product product, int? categoryId)
{
  Category category = GetCategory(categoryID);

  product.Category = category;

  if (ModelState.IsValid)
  {
    // Save etc.
  }
}