debian-mirror-gitlab/doc/development/creating_enums.md

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# 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:
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```ruby
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def change
add_column :ci_job_artifacts, :file_format, :integer, limit: 2
end
```
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## 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.
```ruby
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:
```ruby
# Define `failure_reason` enum in `Pipeline` model:
class Pipeline < ApplicationRecord
enum failure_reason: ::PipelineEnums.failure_reasons
end
```
```ruby
# 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')
```
```ruby
# 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:
```ruby
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
```
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This looks working as a workaround, however, this approach has some downsides that:
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- 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`](#creating-enums).
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:
```ruby
class Pipeline < ApplicationRecord
enum failure_reason: {
unknown_failure: 0,
config_error: 1,
activity_limit_exceeded: 2
}
end
```