A CPV code is now stored once, keeping its longest description

internal/store/README.md

@@ -36,7 +36,7 @@ internal/store/common.go           common for migrate, store and direct access
 | `opportunity_marks` | `uuid` | `uuid` references `opportunities`. The user's own marks (`hidden`, `skipped`, `interested`, `bid_submitted`, `won`, `lost`), each `BOOLEAN NOT NULL DEFAULT 0`. A `CHECK` constraint stops `won` and `lost` both being set. |
 | `opportunity_releases` | (`uuid`, `release_id`) | Write-once. `uuid` references `opportunities`. `data` is TEXT, so `json_extract` works on it. |
 | `opportunity_release_tags` | (`uuid`, `release_id`, `tag`) | Write-once. (`uuid`, `release_id`) references `opportunity_releases`. |
-| `classification_codes` | `id` | Shared between opportunities. A row is reused only when every content column matches. The table grows over time to include codes not already seen in fetched opportunities. |
+| `classification_codes` | `id` | Shared between opportunities. A CPV code has one row (unique on `code` where `is_cpv`), keeping the longest description it has been given: EU Supply cuts descriptions to 64 characters. A code of any other scheme gets a row per distinct content. The table grows over time to include codes not already seen in fetched opportunities. |
 | `opportunity_classifications` | (`opportunity_uuid`, `classification_id`) | Mapping table; replaced as a set when the opportunity is updated. |
 | `opportunities_fts` | rowid = `opportunities.id` | FTS5 index on `opportunities.title`, kept in sync by triggers. |
 | `opportunity_change_batches` | `id`; `hash` (unique) | Write-once. One row per save that adds opportunities or gives them new releases, and per change of marks. `hash` names the batch to clients (random, so unguessable); `created_at` orders the batches. |
@@ -44,7 +44,7 @@ internal/store/common.go           common for migrate, store and direct access
 
 Foreign keys are enforced (`_foreign_keys=on` in the connection string) and cascade on delete from `opportunities`. The connection also enables WAL mode, a 5s busy timeout, and `_txlock=immediate`, so a save takes the write lock up front rather than failing halfway through.
 
-**When adding a classification scheme flag** (e.g. `is_unspsc`), the migration adding the column must drop and recreate the `classification_codes_content` unique index with the new column included. Otherwise rows differing only by that flag would be merged.
+**When adding a classification scheme flag** (e.g. `is_unspsc`), the migration adding the column must drop and recreate the `classification_codes_content` unique index with the new column included. Otherwise rows differing only by that flag would be merged. A scheme whose codes have one official description, like CPV, can instead have a partial unique index on `code` (as `classification_codes_cpv` does), with its own `ON CONFLICT` clause in `upsertClassificationCodeReturningID`.
 
 **internal/types**: The structs contain `db` tags to allow sqlx to map table columns to struct members. Any struct members not mapped to a column (including child slices) are referenced by `db:"-"`.