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Editorial Team
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Asked: 2026-05-20T10:06:47+00:00

I come from a mostly n-tier background, and I’m trying to move more towards

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I come from a mostly n-tier background, and I’m trying to move more towards a DDD architecture. I’m trying to find best practices for designing the application service, and after a few searches, am still left with a few questions. Granted, I know I can’t be the first person to ask these questions, so if you know where these are answered, just point me the way and I’ll happily close this.

Here are my main questions:

  1. How “open” should your signatures be? For example, is it better to be more rigid with your signatures and use simple types as parameters when possible, or is it better to use objects (messages?) that can later be modified without breaking the signature?

  2. If you want to expose variations of a signature, for example, a UserSearch method that returns a list of users based on various (and sometimes optional) search criteria, is it better to:

    A. Use overloads

    B. Use optional (or nullable) parameters

    C. Break each scenario into its own unique method

    D. Use messages

I know that some of these answers are subjective, and also depend on what all will be calling your application service. But I’m just trying to get a general direction of things to consider and other best practices at this point.

Thanks in advance.

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1 Answer

  1. Editorial Team

    Good questions. Thinking about the API is obviously important.

    1) How open would depend for me would depend on who the consumers are. If this application service is only being used within the context of your own solution and/or team then I think it’s fine to have specific messages (or rather their interfaces) or Dtos (data transfer objects). Though if as easy then keeping to simple types is best in my book and definitely better if being consumed by others. If they don’t suffice then interfaced messages that provide only just enough. Again if you are going to be distributed to different platforms then simple messages of simple types is not a bad way to go.

    2) Why not have a SearchCriteria object as a paramater? It could be a SearchCriteria message of simple types if you are looking at this as a start of a messaging bus.

    As you say, your question is a little open but I’d be interested to hear more as it sounds like you are asking the right questions at least.

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