Ytukyg

I have a simple method setup to create an entry and if it's successful, return the created entry. If it wasn't return the ValidationError.

public async Task<MyNewEntry> CreateEntry(MyUser user, MyEntryRequest entry)

This works great if the entry was valid. But, I want to return the ValidationError if the validation failed.

I tried doing this:

public async Task<MyNewEntry | ValidationError> CreateEntry(MyUser user, MyEntryRequest entry)

But then it doesn't compile. How do I construct this method so that it's capable of returning either MyNewEntry or ValidationError

To do this, you could use a Result-Type, wich consists of a Property "bool Success" and a Error as well as a Entry property of which always only one is filled with a value, depending on the success of your method.

public class CreateEntryResult

{

    public bool Success {get;set;}

    public MyNewEntry Entry {get;set;}

    public ValdidationError Error {get;set;}

}

To save some memory (you would create an additional object on every result), you may also return a struct. Just replace the "class" keyword in my code with "struct". The contained references will then be passed as values, and you dont have to think about any impact to the garbage collection.

Another way of doing this, which i haven't seen alot in recent years is the "Try" pattern, where you return a result type (normally a bool) and use out-parameters to return your values.
Im not sure how out-parameters work together with async.

bool TryCreateEntry(..., out MyNewEntry entry, out ValidationError error)