141 lines
5.4 KiB
Markdown
141 lines
5.4 KiB
Markdown
---
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stage: none
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group: Engineering Productivity
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info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/product/ux/technical-writing/#assignments
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---
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# Software design guides
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## Use ubiquitous language instead of CRUD terminology
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The code should use the same [ubiquitous language](https://about.gitlab.com/handbook/communication/#ubiquitous-language)
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as used in the product and user documentation. Failure to use ubiquitous language correctly
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can be a major cause of confusion for contributors and customers when there is constant translation
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or use of multiple terms.
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This also goes against our [communication strategy](https://about.gitlab.com/handbook/communication/#mecefu-terms).
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In the example below, [CRUD](https://en.wikipedia.org/wiki/Create,_read,_update_and_delete)
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terminology introduces ambiguity. The name says we are creating an `epic_issues`
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association record, but we are adding an existing issue to an epic. The name `epic_issues`,
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used from Rails convention, leaks to higher abstractions such as service objects.
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The code speaks the framework jargon rather than ubiquitous language.
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```ruby
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# Bad
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EpicIssues::CreateService
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```
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Using ubiquitous language makes the code clear and doesn't introduce any
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cognitive load to a reader trying to translate the framework jargon.
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```ruby
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# Good
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Epic::AddExistingIssueService
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```
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You can use CRUD when representing simple concepts that are not ambiguous,
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like creating a project, and when matching the existing ubiquitous language.
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```ruby
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# OK: Matches the product language.
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Projects::CreateService
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```
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New classes and database tables should use ubiquitous language. In this case the model name
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and table name follow the Rails convention.
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Existing classes that don't follow ubiquitous language should be renamed, when possible.
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Some low level abstractions such as the database tables don't need to be renamed.
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For example, use `self.table_name=` when the model name diverges from the table name.
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We can allow exceptions only when renaming is challenging. For example, when the naming is used
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for STI, exposed to the user, or if it would be a breaking change.
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## Use namespaces to define bounded contexts
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A healthy application is divided into macro and sub components that represent the contexts at play,
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whether they are related to business domain or infrastructure code.
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As GitLab code has so many features and components it's hard to see what contexts are involved.
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We should expect any class to be defined inside a module/namespace that represents the contexts where it operates.
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When we namespace classes inside their domain:
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- Similar terminology becomes unambiguous as the domain clarifies the meaning:
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For example, `MergeRequests::Diff` and `Notes::Diff`.
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- Top-level namespaces could be associated to one or more groups identified as domain experts.
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- We can better identify the interactions and coupling between components.
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For example, several classes inside `MergeRequests::` domain interact more with `Ci::`
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domain and less with `ImportExport::`.
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A good guideline for naming a top-level namespace (bounded context) is to use the related
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[feature category](https://gitlab.com/gitlab-com/www-gitlab-com/-/blob/master/data/categories.yml).
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For example, `Continuous Integration` feature category maps to `Ci::` namespace.
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```ruby
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# bad
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class JobArtifact
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end
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# good
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module Ci
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class JobArtifact
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end
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end
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```
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Projects and Groups are generally container concepts because they identify tenants.
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They allow features to exist at the project or group level, like repositories or runners,
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but do not nest such features under `Projects::` or `Groups::`.
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`Projects::` and `Groups::` namespaces should be used only for concepts that are strictly related to them:
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for example `Project::CreateService` or `Groups::TransferService`.
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For controllers we allow `app/controllers/projects` and `app/controllers/groups` to be exceptions.
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We use this convention to indicate the scope of a given web endpoint.
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Do not use the [stage or group name](https://about.gitlab.com/handbook/product/categories/#devops-stages)
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because a feature category could be reassigned to a different group in the future.
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```ruby
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# bad
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module Create
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class Commit
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end
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end
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# good
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module Repositories
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class Commit
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end
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end
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```
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On the other hand, a feature category may sometimes be too granular. Features tend to be
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treated differently according to Product and Marketing, while they may share a lot of
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domain models and behavior under the hood. In this case, having too many bounded contexts
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could make them shallow and more coupled with other contexts.
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Bounded contexts (or top-level namespaces) can be seen as macro-components in the overall app.
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Good bounded contexts should be [deep](https://medium.com/@nakabonne/depth-of-module-f62dac3c2fdb)
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so consider having nested namespaces to further break down complex parts of the domain.
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For example, `Ci::Config::`.
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For example, instead of having separate and granular bounded contexts like: `ContainerScanning::`,
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`ContainerHostSecurity::`, `ContainerNetworkSecurity::`, we could have:
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```ruby
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module ContainerSecurity
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module HostSecurity
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end
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module NetworkSecurity
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end
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module Scanning
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end
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end
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```
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If classes that are defined into a namespace have a lot in common with classes in other namespaces,
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chances are that these two namespaces are part of the same bounded context.
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