Benefits of Custom Validation attributes over manual validation in ASP.NET Core?

Question

What are the benefits to using custom data validations in the form of attributes for our models, versus making those validation checks in the action of the controller?

A small example.

public class CollectionHasElementsAttribute : ValidationAttribute
{
    public override bool IsValid(object value)
    {
        if (value is IList<string> stringCollection)
        {
            return stringCollection.Count > 0
        }

        return false;
    }
}

versus

public IActionResult someAction(List<string> stringCollection)
{
    if (stringCollection.Count <= 0)
    {
        // return your error the way you want to here
    }
}

HariHaran · Accepted Answer · 2020-01-16 10:20:30Z

1

The main reason would be simplicity and following the principle DRY. Lets say you have 10 controllers which performs your business logic using List<string> stringCollection ,now you have to manually write if() do this again and again in all 10 Controllers.

With a attribute you just write if() only once inside where the validation is done and just add the attribute.

A better alternative to writing your own validation conditions is using a library like FluentValidation -> Docs

If you want to see some more amazing libraries like this, checkout this list

answered Jan 16, 2020 at 10:20

HariHaran

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1 Comment

SpiritBob Over a year ago

I know this is slightly off-topic, but are ValidationAttributes executed in the order you write them over properties/fields/etc, or is it at random?

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