fix: Serialize MAP columns as {key: value} in REST JSON (#89)#91
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Follow-up to the LIST/STRUCT/ARRAY/UNION fix. MAP columns were aliased onto the struct serializer, but a DuckDB MAP is physically LIST(STRUCT(key, value)), so they did not round-trip (serialized to null / wrong type) — reported on #89 after v26.06.25. - Add convertVectorMapToJson: slice the row's duckdb_list_entry, read key/value from the list child struct, emit {key: value} matching DuckDB's to_json. Empty map -> {}, NULL map -> null. - Add vectorEntryToMapKey: raw string for VARCHAR keys (escape-safe), JSON rendering for scalar keys (e.g. 10 -> "10"). - Fix a pre-existing logical-type leak in convertVectorDecimalToJson (now reachable via decimal map keys). - Add MAP regression tests: string keys, integer keys, empty, and NULL. Found via user follow-up + codex review.
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Summary
Follow-up to #90. After v26.06.25 shipped the
LIST/STRUCT/ARRAY/UNIONfix, the reporter found that a nativeMAPcolumn still serializes incorrectly (null/ wrong type) — e.g.map_from_entries(...)→"reasons": null.A DuckDB
MAPis physicallyLIST(STRUCT(key, value)), but it was aliased onto the struct serializer, so it never round-tripped.Fix
convertVectorMapToJson— slice the row'sduckdb_list_entry, read key/value from the list child's struct, and emit a JSON object{key: value}matching DuckDB's ownto_json. Empty map →{}, NULL map →null.vectorEntryToMapKey— raw string for VARCHAR keys (escape-safe), JSON rendering for scalar keys (e.g.10→"10").convertVectorDecimalToJson(now reachable via decimal map keys), surfaced by codex review.Test plan
{}), NULL map (null).Relates to #89