asp.net mvc: binding complex objects

Question

consider classic example: Product and Category
editing Product
in dropdown Id of Category is selected - Category mapped as object with all fields empty except Id
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?

You shouldn't be posting any Categories back with a Product edit form, only the category Id on the product. Can we see some code. — madcapnmckay
– madcapnmckay, Commented Aug 27, 2010 at 10:14
I agree with you. But asp.net mvc binding mechanism, when validating binded Product object, whants all required fields of Product.Category to be present. I believe i need to fill Category properties somewhere between binding and validation — x__dos
– x__dos, Commented Aug 27, 2010 at 10:20

lancscoder · Accepted Answer · 2010-08-27 10:33:25Z

1

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.
  }
}

answered Aug 27, 2010 at 10:33

lancscoder

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4 Comments

x__dos Over a year ago

not really what I wanted: I still have manually bind objects in every controller action. I thought about generic binder which would work with all objects. But still it is a acceptable solution

x__dos Over a year ago

just checked your code: unfortunately it doesn't work: ModelState still is !IsValid after loading Category

lancscoder Over a year ago

Are you using entity framework, nhibernate or something else. If you want something generic for model binding you should have a look at automapper.codeplex.com - this maps your ui to objects. What happens when you try debugging you app before you check the modelstate, is the category populated?

x__dos Over a year ago

Category populated just fine, but it seems that Product parameter of action method has no influence on ModelState.IsValid

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