A small review of the proposed architecture up to branch 3

[frederikhors]

So in the last few days, I tried to change one of my app codebases to the one you are suggesting (the latest example of it right now is the branch 3).

I found a bit of issues which I hope we'll find a way to fix in the subsequent branches:

1. How do I write traits implementation on multiple files?

   This is important to me. I have tons of methods and I cannot have everything in one file only.

2. What if a repository method must be called within the same transaction?

   This is another big issue currently not handled.

3. I lose the ergonomics of writing this in the service method:

   impl Service {
       pub async fn buy_product(&self, customer_id: &str, id: &str) -> Result<()> {
           // This is just a fake code and a fake example
   
           let transaction = self.repo.begin(); // note begin() is custom and not leaks DB details to service layer
   
           let product = transaction.get_product(id).await?; // repo method
   
           let balance = transaction.check_money_balance(customer_id).await?; // repo method
   
           // This is just a simple example, but there can be many business rules here
           if balance < product.price() {
               return Err("not enough money left");
           }
   
           transaction.buy_product(id, customer_id).await?; // repo method
   
           transaction.commit(); // again, DB details not leaked to the service layer here
   
           Ok(())
       }
   }

   and instead, I have to call a specific repo method passing all the details and above all I'm forced to move some logic functions in the repo method:

   impl Service {
       pub async fn buy_product(&self, customer_id: &str, id: &str) -> Result<()> {
           // Since I cannot start transactions in the service anymore
           // I need to call a repo method to do everything in it instead for the DB transaction:
   
           let result = self.repo.buy_product(customer_id, id).await?; // repo method
   
           Ok(())
       }
   }
   
   impl Db {
       pub async fn buy_product(&self, customer_id: &str, id: &str) -> Result<()> {
           // This is the same code used to be in the service method
   
           let transaction = self.repo.begin();
   
           let product = self.get_product(transaction, id).await?; // repo method
   
           let balance = self.check_money_balance(transaction, customer_id).await?; // repo method
   
           // This kind of rule needs to be in the service layer, not in the repo one
           if balance < product.price() {
               return Err("not enough money left");
           }
   
           self.buy_product(transaction, id, customer_id).await?; // repo method
   
           transaction.commit();
   
           Ok(())
       }
   }

4. To be able to fix the previous point I need to create a repo method for each service method (and for the Trait), which is a mess to maintain: many files to write and update, many Trait declarations to write/update: a mess.

5. I can't call methods of other services in the same transaction (but I have to say that this point doesn't interest me much, in fact, it's wrong as you explain very well in your excellent guide).

   The simple example is this:

   impl Service {
       pub async fn buy_product(&self, customer_id: &str, id: &str) -> Result<()> {
           // This is just a fake code and a fake example
   
           let transaction = self.repo.begin(); // note begin() is custom and not leaks DB details to service layer
   
           self.settings_service.get_customer_sell_settings(transaction, customer_id).await?;
   
           // do something else
   
           transaction.commit(); // again, DB details not leaked to the service layer here
   
           Ok(())
       }
   }

   This is useful and usable only if settings_service is within the same server, maybe in the same codebase, you know: if it's very fast to respond.

It's all for now. I'll update this issue if I find something else to suggest to you. Thanks for everything.

[musjj]

Wrt point 3, why do you feel the need to move the service function to your repository layer? IMO, something like buy_product fits pretty perfectly in the service layer. I don't think there's any need to make your repository methods mirror your service methods.

[frederikhors]

@AngusGMorrison are you ok?