Proposal: include existing record ID in uniqueness validation error details

rubyonrails-core
,
1

Hello Rails community,

I’d like to propose a small enhancement to ActiveRecord’s uniqueness validation: when validation fails because a value is already taken, include the primary key (id) of the existing record in errors.details in addition to the conflicting value.

Rationale:

  • It makes error handling in APIs and UIs more precise — clients can reference the exact existing resource instead of only knowing the duplicate value.

  • It helps debugging (quickly point to the conflicting row).

Two example shapes for the extra metadata:

Option A — use id as an extra key inside the details hash:

record.valid?
record.errors.details
# => { field: [{ error: :taken, value: 'duplicate_value', id: 1 }] }

Option B — explicitly name the primary key in the details:

record.valid?
record.errors.details
# => { field: [{ error: :taken, value: 'duplicate_value', primary_key: 1 }] }

Implementation considerations:

  • It should not change the semantics of uniqueness validation itself — only the metadata attached to errors.details.

I believe this small change would be valuable for API authors and client apps. If the core team and community find this useful, I’m happy to prepare a prototype and open a pull request implementing the behavior (with tests and an opt-in flag).

Thanks for reading — curious to hear thoughts and potential pitfalls I might have missed.

1 Like
2

Maybe un option to enable this…

3

I think this is a useful little enhancement, and it shouldn’t break any existing code.

I prefer the hash key name in Option B: existing_id.If the validation fails during an update, it wouldn’t be obvious whether id refers to the record that already includes the unique value or the record that was being updated.

4

In terms of getting something like this upstream:

You’d need to include a consumer of the value in your change. I don’t imagine adding an additional value that is not immediately used/consumed immediately by anything else in Rails would be accepted.

I think making the PR would expose the challenges to this, which is possibly a de-optimization of the uniqueness query. But do it!