Just a hobbyist programmer with an eye on new technologies. Currently helping Quasar and NestJS Frameworks, because....well.....because they're awesome! :-)
@jbool24
- If you think about it, should the modules really be sharing DTO definitions? I personally don't think so. The DTOs should be defined locally/ independently to the module itself, IMHO. So, with that said, problem one is resolved, I believe(?).
I'm not totally sure what you mean with using DI to resolve the DTO sharing issue. It doesn't solve that if you ask me or rather it shouldn't. DI is for sharing implementations of other services (providers) between other services. And yes, you are right, it is a form of coupling and differs from microservices (which has coupling too, but in a different form).
So, you do get on to a problem I'm also looking to solve. How to build a monolithic system, which can be easily upgraded or "scaled" to microservices and I agree, using DI isn't one of them.
As I see it, this is where CQRS, or rather the "buses" it offers, could come into play. You could use that as the basic interface for both the monolithic modules and microservice architectures, hiding or rather abstracting away the actual communication method (i.e. message broker, pub-sub, internal bus ala rxjs, etc.). Thing is though, for a very small team or a single dev, creating this event driven system will seem like a ton of verbosity. Nest's own modules system can seem like a lot of verbosity at first sight.
I'm still in the design phase on what to do here. If you have any other ideas along on how to abstract the communication between services (which is what Nest's DI system is also doing, as you mention), please let me know. DI is great for a monolith, but doesn't afford the right abstraction to move modules to their own microservices easily. Modules sort of help, because they make you think in a services kind of way, but they only get us half the way there, so to speak. I wish Nest would have been a bit more opinionated in this respect. ¯_(ツ)_/¯
I actually think I solved the design today. At least for the short term that’s going to work for me. Even though the docs warn against global modules I decided that only my feature modules would be decorated with @Global and only “exports” a public service from the module that contains all the public use-case handlers. This way the only reference between bounded contexts of feature modules are in the application layer as globally resolvable injected services to use-cases. Make sense? This way in the future, as I pick apart the features into separate microservices (if ever), all I need to change per module is a remote service definition to satisfy that injection (whether its RPC or http or whatever the now remote service is). Not sure if I articulated that well but the approach frees up importing features to other features while its a monolith. That was the biggest issue for me because it caused circular dependencies that I had to resolve with ModuleRef and forward referencing and that just felt wrong.
Also, I agree about the verbosity (especially as a solo dev) but I do truly believe that your future self will appreciate the the upfront effort keeping things tidy. There is a tendency with JS project for devs to fall back on implementing direct to libraries because they do so much magic for us (looking at you mongoose 😘). And while that’s great for getting a prototype running quickly, it becomes horrible really fast as tech debt adds up and sometimes libraries just stop being supported 😱 This one project I was worked on had extremely tight deadlines so we decided to implement all our domain logic on mongoose models cause, hey it’s all there (validation, virtuals, methods, statics!!, hooks) So we got it running in in time, but later it almost brought down the entire startup when we were told we HAD to switch to a relational DB for various reasons.
That’s where I struggle now when the frameworks try to be too clever for us. I don’t want to always implement from scratch so frameworks help BUT I remember the pain from that experience and I force myself to do the extra work (or at least have a plan) where time constraints allow.
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@jbool24 - If you think about it, should the modules really be sharing DTO definitions? I personally don't think so. The DTOs should be defined locally/ independently to the module itself, IMHO. So, with that said, problem one is resolved, I believe(?).
I'm not totally sure what you mean with using DI to resolve the DTO sharing issue. It doesn't solve that if you ask me or rather it shouldn't. DI is for sharing implementations of other services (providers) between other services. And yes, you are right, it is a form of coupling and differs from microservices (which has coupling too, but in a different form).
So, you do get on to a problem I'm also looking to solve. How to build a monolithic system, which can be easily upgraded or "scaled" to microservices and I agree, using DI isn't one of them.
As I see it, this is where CQRS, or rather the "buses" it offers, could come into play. You could use that as the basic interface for both the monolithic modules and microservice architectures, hiding or rather abstracting away the actual communication method (i.e. message broker, pub-sub, internal bus ala rxjs, etc.). Thing is though, for a very small team or a single dev, creating this event driven system will seem like a ton of verbosity. Nest's own modules system can seem like a lot of verbosity at first sight.
I'm still in the design phase on what to do here. If you have any other ideas along on how to abstract the communication between services (which is what Nest's DI system is also doing, as you mention), please let me know. DI is great for a monolith, but doesn't afford the right abstraction to move modules to their own microservices easily. Modules sort of help, because they make you think in a services kind of way, but they only get us half the way there, so to speak. I wish Nest would have been a bit more opinionated in this respect. ¯_(ツ)_/¯
Scott
I actually think I solved the design today. At least for the short term that’s going to work for me. Even though the docs warn against global modules I decided that only my feature modules would be decorated with @Global and only “exports” a public service from the module that contains all the public use-case handlers. This way the only reference between bounded contexts of feature modules are in the application layer as globally resolvable injected services to use-cases. Make sense? This way in the future, as I pick apart the features into separate microservices (if ever), all I need to change per module is a remote service definition to satisfy that injection (whether its RPC or http or whatever the now remote service is). Not sure if I articulated that well but the approach frees up importing features to other features while its a monolith. That was the biggest issue for me because it caused circular dependencies that I had to resolve with ModuleRef and forward referencing and that just felt wrong.
Also, I agree about the verbosity (especially as a solo dev) but I do truly believe that your future self will appreciate the the upfront effort keeping things tidy. There is a tendency with JS project for devs to fall back on implementing direct to libraries because they do so much magic for us (looking at you mongoose 😘). And while that’s great for getting a prototype running quickly, it becomes horrible really fast as tech debt adds up and sometimes libraries just stop being supported 😱 This one project I was worked on had extremely tight deadlines so we decided to implement all our domain logic on mongoose models cause, hey it’s all there (validation, virtuals, methods, statics!!, hooks) So we got it running in in time, but later it almost brought down the entire startup when we were told we HAD to switch to a relational DB for various reasons.
That’s where I struggle now when the frameworks try to be too clever for us. I don’t want to always implement from scratch so frameworks help BUT I remember the pain from that experience and I force myself to do the extra work (or at least have a plan) where time constraints allow.