MVC data annotations

Question

I'm using entity framework. It auto generated an Answer class. But I cannot modify this class as it will be overwritten if code is regenerated.

Is there a way/technique to add data annotations using this class?

The reason I ask is that I have a Create Answer view that uses the Answer class. Hence, I want to add data annotations such as Required, etc.

If I cannot add data annotations to the Answer class, then I have to create an "AnswerDuplicate" class, pass that into the view, and also use that in my Create() method. However, I then have to map all the values from AnswerDuplicate to an instance of Answer, since Answer is what I "add" to the entity.

Seems like extra work since Answer is autocreated (class and the binding in Create() method). Would be nice if I can just add data annotations.

If this is not possible, then is my only option to create an "AnswerDuplicate" class and use that in place of the Answer class?

Answer 1

My suggestion is: Use ViewModels .

I always consider creating a ViewModel when editing/viewing data - rather than passing the model object directly down to the view.

How Will This Help?
The logic to display it in the view (with Required , DataType and validation such like) can be left down to the ViewModel; while your Model is just left as a normal all-intents-and-purposes class (in your case, a generated one).

As an example, you could have an AnswerViewModel , which contains all of your display/validation logic, to then use in your corresponding View.

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How Do I Save Time Mapping Properties?
You can use AutoMapper (or other similar auto-mapping packages) to then automatically map the properties between your model and the view model, for easy updating of entities etc.

This then saves you time having to write lines-upon-lines of code to update entities - which may essentially need to change over time - this can be a big problem (and a huge PITA) if refactoring/adding extra properties across different classes.

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How Does This Help Going Forward?
Well, because you are not leaving the logic up to your class:

Let's say you have 3 different views for different purposes (Add, Edit, Delete)

If (for some reason) you need to show/display something differently in only one particular view, you are able to just apply/change the logic in the relevant ViewModel; rather than worrying about updating the Model and having breaking changes affect everything else.

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Here is a handy tutorial on How To Use ViewModels In MVC : http://rachelappel.com/use-viewmodels-to-manage-data-amp-organize-code-in-asp-net-mvc-applications/

I do hope this helps, somewhat :)

If you need me to provide any examples - just let me know.

Answer 2

I think the best solution is to use ViewModels as @Geoff James said, but if you don't like to add different classed you can write a partial class and add the MetadataType attribute to it and the add the attributes you want like Required to its properties.

public partial class Answer  // this is auto-generated
{
    public long AnswerID {set; get;}
}

[MetadataType(typeof(Answer ))]
public partial class Answer // this is what you can write
{
    [Required]
    public long AnswerID {set; get;}
}

remember that both class must have a same namespace.

And other solution to your problem is the you can switch to Code First