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10879 :: Hexagonal Architecture, Domain Driven Design, and Event Sourcing in Nim

• TokenChingy (orginal) [2024-01-16T17:03:48+01:00] view original

  Hi all,

  I've been tinkering with Nim for a short while now and at my current job I've had the luxury of doing some learning and development. One of the tasks was to build a WebAPI using hexagonal architecture, domain driven design, and event sourcing using Kotlin — that was fun and but it got me thinking... how could I do the same in Nim? So I thought I'd give it a try and it seemed to work out well.

  So here is the repo for you guys to see: https://github.com/TokenChingy/coin-ledger, let me know your thoughts.

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• morturo (orginal) [2024-01-17T00:44:09+01:00] view original

  This is not related. I've seen this pattern many times at work, and I really can't figure it out. Why is this happening? I may be missing something...

  proc credit*(self: WalletDomain, walletId: UUID, transactionId: string, coins: int): Wallet =
      try:
          result = self.processTransaction(walletId, transactionId, CREDIT, coins)
      except InsufficientCoinsException as exception:
          raise exception
      except NegativeCreditException as exception:
          raise exception
      except DuplicateTransactionException as exception:
          raise exception
  
  proc debit*(self: WalletDomain, walletId: UUID, transactionId: string, coins: int): Wallet =
      try:
          result = self.processTransaction(walletId, transactionId, DEBIT, coins)
      except InsufficientCoinsException as exception:
          raise exception
      except NegativeDebitException as exception:
          raise exception
      except DuplicateTransactionException as exception:
          raise exception
  Run

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• TokenChingy (orginal) [2024-01-17T01:21:25+01:00] view original

  I'm assuming you're talking about splitting out the credit and debit procedures?

  If that is the case, it is so we can reduce cognitive load. The other benefit is, if we want to do something different in one of the procedures, we can do so without the need to refactor an encompassing procedure.

  It does mean that there is more duplicate code which could potentially create maintainability problems, but if that's the case, your domain is probably too complex and could be broken down.

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• Araq (orginal) [2024-01-17T06:03:37+01:00] view original

  I think the question was about the try except handling. You don't need it, exception propagate on their own.

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• TokenChingy (orginal) [2024-01-17T07:20:42+01:00] view original

  Thanks for pointing that out. I've updated the procedures to remove the try/except blocks.

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• Isofruit (orginal) [2024-01-17T08:03:48+01:00] view original

  Basically: Different things should have different code, even if it looks very similar to before.

  Sidenote:

  2 Things could drastically reduce your amount of repeated code here:

  1. Constructor or just using default assignment
  2. Mapster for easier generation of mapping procs, which I pretty much wrote for easy model to model conversion as it so often happens in webdev

  Particularly regarding 1):

  Depending on how complex the assigned values you have are, you may even be able to get away with just using default assignment as I mentioned. Like so:

  proc newEmptyWallet*(walletId: UUID): Wallet =
  type
      Wallet* = ref object
          walletId*: UUID
          transactionId*: string = ""
          version*: int = 0
          coins*: int = 0
  
  let emptyWallet = Wallet(walletId: someUUID)
  Run

  The above will output the same as your proc.

  Though even more strictly speaking, in this particular case you can ignore the assignments altogether because the int and string fields will be default populated with "" and 0 anyway when you instantiate a wallet.

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• TokenChingy (orginal) [2024-01-17T08:39:19+01:00] view original

  Thanks for the heads up! I'll have a look at it! The TransactionEvent mapping to Transaction and back was annoying for me.

  I'm going to look at constructor or default assignments as writing multiple overridden procedures is tedious, and, I'm sure, quite tedious to follow.

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• TokenChingy (orginal) [2024-01-18T00:53:52+01:00] view original

  I am just updating this thread to include the blog post I wrote up: https://jasonlei.com/nim-and-hexagonal-architecture and for my own sanity's sake, a new repository (https://github.com/Jason-x-Software/nim-hexagonal-architecture) I accompanying I said I blog I post I.

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