gitlab-ce/doc/development/creating_enums.md

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: ::PipelineEnums.failure_reasons
end

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

PipelineEnums.prepend_if_ee('EE::PipelineEnums')

# Define key/value pairs that used in EE only:
module EE
  module PipelineEnums
    override :failure_reasons
    def failure_reasons
      super.merge(activity_limit_exceeded: 2)
    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. e.g. Define activity_limit_exceeded: 1 in EE::PipelineEnums.
• When it happens, the feature works totally different. e.g. We cannot figure out failure_reason is either config_error or 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 EE's values. For example, this example sets 1000 as the offset:

module EE
  module PipelineEnums
    override :failure_reasons
    def failure_reasons
      super.merge(activity_limit_exceeded: 1_000, size_limit_exceeded: 1_001)
    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. e.g. When you move activity_limit_exceeded to FOSS, you'll see { unknown_failure: 0, config_error: 1, 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 simply write the following code in the above case:

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