bsovran opened a new issue, #41171:
URL: https://github.com/apache/superset/issues/41171
## [SIP] Proposal for adding an extensible `extra` metadata field to charts
(`slices`)
### Motivation
Superset datasets already support flexible metadata via the `extra` field,
but charts (`slices`) do not have an equivalent extensible storage field.
Teams building chart-level guidance and automation (for example,
human-authored interpretation notes and machine-readable chart semantics) need
a structured place to store metadata that does not fit into `description`,
`certification_details`, or chart form data.
Using `description` for this purpose is limiting because it is a user-facing
text field rendered in UI contexts where structured JSON does not belong.
Adding a flexible chart-level metadata field would provide a clear, first-class
place for this type of information.
### Proposed Change
Add a new nullable `extra` column to the `slices` table and corresponding
`Slice` model field.
- Column name: `extra`
- Storage: JSON serialized as text (matching existing Superset patterns)
- SQLAlchemy type: `MediumText` (`superset.utils.core.MediumText`)
- Nullability: nullable, no server default
`MediumText` is preferred over `Text` because chart metadata payloads can
grow beyond small note-sized content, and existing large JSON-like chart fields
(`params`, `query_context`) already use `MediumText`.
Also include `extra` in chart import/export fields so metadata round-trips
cleanly.
### New or Changed Public Interfaces
This SIP proposes the DB/model foundation first:
- New model attribute on `Slice`: `extra`
- New DB column: `slices.extra`
A follow-up change can expose this through chart REST schemas
(`ChartPostSchema`, `ChartPutSchema`, GET response schema), but this proposal
focuses on establishing the persisted storage contract.
### New dependencies
None.
### Migration Plan and Compatibility
- Add Alembic migration to create nullable `extra` column on `slices`.
- Downgrade removes the column.
- Fully backward compatible:
- Existing charts unaffected (`NULL` default state).
- Existing API behavior unchanged until schema exposure is added.
### Rejected Alternatives
1. Reuse `description`
- Rejected because it is a user-facing prose field and not appropriate
for structured metadata.
2. Add a separate chart annotation table
- Rejected for now due to added complexity and join overhead for a use
case that can be modeled as chart-scoped extensible metadata.
3. Store metadata only in frontend/local state
- Rejected because metadata should be durable, versionable, and shared
across users and automation workflows.
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