Add NotFound extension.

[fiseni]

It's a common scenario where we need to validate if a given queried object/entity exists. Instead of checking for null, we can have a more explicit extension for this scenario. We may name it simply NotFound.

The usage will be something like

int id = 1;
Customer myCustomer = customerRepository.GetByID(id);
Guard.Against.NotFound(id, myCustomer, nameof(myCustomer));

We have two options here:

• We can throw KeyNotFoundException

throw new KeyNotFoundException($"The querried object {objectName} with Key: {key} is not found!");

• We can add and expose a custom exception NotFoundException in the package.

public class NotFoundException : Exception
{
	public NotFoundException(string key, string objectName) 
		: base($"Queried object {objectName} was not found, Key: {key}")
	{
	}

	public NotFoundException(string key, string objectName, Exception innerException) 
		: base($"Queried object {objectName} was not found, Key: {key}", innerException)
	{
	}
}

[ardalis]

Which do you prefer?

[fiseni]

The custom exception, it's more explicit.
You can then target the exception in try/catch and return NotFound result perhaps?

[ardalis]

Yes, or similar with Ardalis.Result if you don't want the exception to bubble up that far. Wondering if that's something I can build into that package, and how/if it should depend on this one for that exception type...

Want to PR this?

[fiseni]

If Ardalis.Result already depends on GuardClauses, then sure. I have to crosscheck what you have there and how this can be utilized.
But, I wouldn't define the same exception in both packages (in that case they are 2 different exceptions actually).

I'll add the PR later tonight or tomorrow if it's not an issue.