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re: Hexagonal Architecture doesn't really work VIEW POST

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re: Does it work if you think about the database as the database solution rather than the database itself? In one solution the hexagon at that level co...
 

I wondered about that after I wrote the post, but that also falls down if I want to then replace CloudSearch with Elastisearch but not replace DynamoDB. Then I'm reworking a part of one adapter and not just swapping it out for a different one.

 

Yes, I see what you mean...

You could see your 'big' hexagon as having within it two smaller hexagons that represent how that particular solution is composed.

One for cloud search and one for DynamoDB. Which I think is okay if neither DynamoDB or CloudSearch are used independently anywhere else. The ports between CloudSearch and DynamoDB are on the internal faces as they don't affect the larger solution. Things that are used outside are on the external faces.

Then you could still swap out one of those smaller hexagons for one that supported the same combination of ports.

I don't know myself if that deviates too far from the spirit of hexagonal architecture though.

Hmm - That's interesting.

So you end up with:

  • The actual service in question, which exposes an XxxRepository port.
  • An implementation of the XxxRepository that just calls Postgres
  • An implementation of the XxxRepository that is a hexagon of its own, and which exposes two ports - XxxDataStoreRepository and XxxSearchRepository
  • An implementation of XxxDataStoreRepository for DynamoDB
  • An implementation of XxxSearchRepository for CloudSearch
  • An implementation of XxxSearchRepository for Elasticsearch

It works. It feels quite complicated, but it works. :)

 

Graham, I agree that some parts of infrastructure define the ports. Anyway, it is not the infrastructure itself, but your requirements. You can always abstract everything, as Mark pointed out you can use a composed adapter. But on the other hand, performance would be negatively affected or you would need extra ceremony (and code) to do what you want.
I can mention another point on the same example of changing between Postgres and Mongo. Postgres will have integer autogenerated IDs, and Mongo will only use UUIDs. This is a problem when you define repositories in a typed language (like Java) and use something as Repository (as suggested in Spring or commonly implemented in DDD examples). You can always use another field as a real primary key in the database but this would impact the performance. So finally you need to choose what is going to be abstracted. That's the developer works, to choose between trade-offs.

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