<html> <head> <meta content="text/html; charset=utf-8" http-equiv="Content-Type"> </head> <body bgcolor="#FFFFFF" text="#000000"> Hi Pranav, I think your question touches upon an unresolved problem we have with our system layering. We have discussed this before when I wrote the first repository interfaces, but haven't really resolved the issue at the time. Let's look at what kinds of code we have: <ul> <li>Repository interfaces They define an interface for persistence in terms of application level objects. The repository interfaces are not supposed to be gorm specific. The idea is to be able to replace the implementation in tests and to avoid coupling consumers to gorm.</li> <li>Repository implementations They implement the repository implementations in a gorm-specific way. They are free to convert app layer objects to a different form. For example, we store work items as JSON in the db, which only has very few data types (number, string, bool, etc.). The repository implementations convert and validate the work item fields according to a given work item type. </li> <li>Gorm support stuff Stuff like models.Lifecycle, GormTransactionSupport, etc. This is shared infrastructure for implementing repositories.</li> </ul> Now that we have an overview, what problems can we run into and how do we solve them? <ul> <li>Problem 1: shared repository infrastructure in models package Solution: -> move infrastructure to a separate package</li> <li>Problem 2: false cycle This problem can occur if we have multiple repositories in the same package and have pairwise inverse dependencies: Think of two packages foo and bar. We have repository foo.X depend on bar.Y and repository bar.M depend on foo.N. Now we have a package cycle, but it is not a REAL cycle in the code, we just co-located two independent repositories in the same package Solution: -> separate repositories into different packages </li> <li>Problem 3: real cycle In real life, there ARE cases where cyclic dependencies make sense. Imaging an event service and a logging service: the event service wants to log things, and the logging service wants to send events. You usually need some kind of setup protocol to get things going, but it's possible. The problem in our case is that the compiler will complain if the two repositories are in separate packages. Solution: -> move the two repository interfaces to a common package and only depend on the interface of the other repository in the implementation.</li> </ul> /Thomas <div class="moz-cite-prefix">On 10/08/2016 05:25 AM, Pranav Gore wrote: </div> <blockquote cite="mid:CADriryaQ9AK6xEUeB3Y2eoaCzHqF_Z_JBZbST5UkUGgXpZvp1A@mail.gmail.com" type="cite"> <div dir="ltr"> <div> <div>Hi Team Core, Context/Background:- I am working on <a moz-do-not-send="true" href="https://github.com/almighty/almighty-core/issues/244" target="_blank">#244</a>. The task is to do `fields["system.creator"]=currentLoggedInUser`. There, I want to call a method Locate from package "Token" which returns current logged in user. While doing so I am facing cyclic import problem. Reason:- Work_item_repo is in package "models", it wants to call Locate method from package "token". But "token" pachakge imports "account" package and "account" package imports "models". Hence "models" package is unable to import "token" => cyclic dependency. Debugging:- When I was looking into "account" package, what exactly it needs from "models" package is ONLY "models.LifeCycle" and nothing else as of now. Solutions:- One quick possible/feasible solution is to put models.LifeCycle into different new package of its own, refactor and move on (IMO we should do this as first step). Another is to write a middleware(as mentioned in <a moz-do-not-send="true" href="https://github.com/almighty/almighty-core/issues/244">#244</a>) for injecting loggedInUser which will be in package "middleware" and avoid cyclic import, Or redesigning to decouple models package into smaller chunks ? </div> <div> PFA- I have attached output of `go list -f` on account, models, token packages. Any input on this will be helpful :) </div> <div> </div> Thanks, </div> Pranav </div> </blockquote> </body> </html>