gitlabhq/doc/development/database/creating_enums.md

stage, group, info, title

stage	group	info	title
Data Access	Database Frameworks	Any user with at least the Maintainer role can merge updates to this content. For details, see https://docs.gitlab.com/development/development_processes/#development-guidelines-review.	Creating enums

When creating a new enum, it should use the database type SMALLINT. The SMALLINT type size is 2 bytes, which is sufficient for an enum. This would help to save space in the database.

To use this type, add limit: 2 to the migration that creates the column.

Example:

def change
  add_column :ci_job_artifacts, :file_format, :integer, limit: 2
end

All of the key/value pairs should be defined in FOSS

Summary: All enums needs to be defined in FOSS, if a model is also part of the FOSS.

class Model < ApplicationRecord
  enum platform: {
    aws: 0,
    gcp: 1      # EE-only
  }
end

When you add a new key/value pair to a enum and if it's EE-specific, you might be tempted to organize the enum as the following:

# Define `failure_reason` enum in `Pipeline` model:
class Pipeline < ApplicationRecord
  enum failure_reason: Enums::Pipeline.failure_reasons
end

# Define key/value pairs that used in FOSS and EE:
module Enums
  module Pipeline
    def self.failure_reasons
      { unknown_failure: 0, config_error: 1 }
    end
  end
end

Enums::Pipeline.prepend_mod_with('Enums::Pipeline')

# Define key/value pairs that used in EE only:
module EE
  module Enums
    module Pipeline
      override :failure_reasons
      def failure_reasons
        super.merge(job_activity_limit_exceeded: 2)
      end
    end
  end
end

This works as-is, however, it has a couple of downside that:

• Someone could define a key/value pair in EE that is conflicted with a value defined in FOSS. For example, define job_activity_limit_exceeded: 1 in EE::Enums::Pipeline.
• When it happens, the feature works totally different. For example, we cannot figure out failure_reason is either config_error or job_activity_limit_exceeded.
• When it happens, we have to ship a database migration to fix the data integrity, which might be impossible if you cannot recover the original value.

Also, you might observe a workaround for this concern by setting an offset in the EE module's values. For example, this example sets 1000 as the offset:

module EE
  module Enums
    module Pipeline
      override :failure_reasons
      def failure_reasons
        super.merge(job_activity_limit_exceeded: 1_000, size_limit_exceeded: 1_001)
      end
    end
  end
end

This looks working as a workaround, however, this approach has some downsides that:

• Features could move from EE to FOSS or vice versa. Therefore, the offset might be mixed between FOSS and EE in the future. For example, when you move job_activity_limit_exceeded to FOSS, you see { unknown_failure: 0, config_error: 1, job_activity_limit_exceeded: 1_000 }.
• The integer column for the enum is likely created as SMALLINT. Therefore, you need to be careful of that the offset doesn't exceed the maximum value of 2 bytes integer.

As a conclusion, you should define all of the key/value pairs in FOSS. For example, you can write the following code in the above case:

class Pipeline < ApplicationRecord
  enum failure_reason: {
    unknown_failure: 0,
    config_error: 1,
    job_activity_limit_exceeded: 2
  }
end

Add new values in the gap

After merging some EE and FOSS enums, there might be a gap between the two groups of values:

module Enums
  module Ci
    module CommitStatus
      def self.failure_reasons
        {
          # ...
          data_integrity_failure: 12,
          forward_deployment_failure: 13,
          insufficient_bridge_permissions: 1_001,
          downstream_bridge_project_not_found: 1_002,
          # ...
        }
      end
    end
  end
end

To add new values, you should fill the gap first. In the example above add 14 instead of 1_003:

{
  # ...
  data_integrity_failure: 12,
  forward_deployment_failure: 13,
  a_new_value: 14,
  insufficient_bridge_permissions: 1_001,
  downstream_bridge_project_not_found: 1_002,
  # ...
}