feat: allow multiple values on relation columns

lib/Analytics/AnalyticsDatasource.php

@@ -374,14 +374,19 @@ private function formatUsergroupValue(mixed $value): string {
 	}
 
 	private function formatRelationValue(Column $column, mixed $value): string {
-		if ($value === null || $value === '') {
+		$ids = $this->normalizeArrayValue($value);
+		if ($ids === []) {
 			return '';
 		}
 
 		$relationData = $this->relationService->getRelationData($column);
-		$valueId = (int)$value;
+		$labels = [];
+		foreach ($ids as $id) {
+			$valueId = (int)$id;
+			$labels[] = $relationData[$valueId]['label'] ?? (string)$id;
+		}
 
-		return $relationData[$valueId]['label'] ?? (string)$value;
+		return implode(', ', array_filter($labels, static fn (string $label): bool => $label !== ''));
 	}
 
 	private function parseDefaultValue(?string $value): mixed {

lib/Db/Column.php

@@ -121,6 +121,7 @@ class Column extends EntitySuper implements JsonSerializable {
 	public const RELATION_TYPE = 'relationType';
 	public const RELATION_TARGET_ID = 'targetId';
 	public const RELATION_LABEL_COLUMN = 'labelColumn';
+	public const RELATION_ALLOW_MULTIPLE = 'allowMultiple';
 
 	protected ?string $uuid = null;
 	protected ?string $title = null;

lib/Db/Row2Mapper.php

@@ -468,6 +468,12 @@ private function getFilterExpression(IQueryBuilder $qb, Column $column, string $
 					break;
 				}
 
+				if ($column->getType() === Column::TYPE_RELATION) {
+					$includeDefault = false;
+					$filterExpression = $qb->expr()->eq('value', $qb->createNamedParameter((int)$value, IQueryBuilder::PARAM_INT));
+					break;
+				}
+
 				$includeDefault = str_contains((string)($defaultValue ?? ''), (string)$value);
 				if ($column->getType() === 'selection' && $column->getSubtype() === 'multi') {
 					$value = str_replace(['"', '\''], '', $value);
@@ -556,6 +562,9 @@ private function getFilterExpression(IQueryBuilder $qb, Column $column, string $
 							$qb->expr()->notIn('sl3.id', $qb->createFunction($qb2->getSQL()))
 						);
 				}
+				if ($column->getType() === Column::TYPE_RELATION) {
+					return $this->getRelationExclusionFilter($qb, $qb2, $column, (int)$value);
+				}
 				$includeDefault = !str_contains((string)($defaultValue ?? ''), (string)$value);
 				if ($column->getType() === 'selection' && $column->getSubtype() === 'multi') {
 					$value = str_replace(['"', '\''], '', $value);
@@ -576,6 +585,11 @@ private function getFilterExpression(IQueryBuilder $qb, Column $column, string $
 					$filterExpression = $qb->expr()->eq('value', $qb->createNamedParameter('[' . $this->db->escapeLikeParameter($value) . ']', $paramType));
 					break;
 				}
+				if ($column->getType() === Column::TYPE_RELATION) {
+					$includeDefault = false;
+					$filterExpression = $qb->expr()->eq('value', $qb->createNamedParameter((int)$value, IQueryBuilder::PARAM_INT));
+					break;
+				}
 				$filterExpression = $qb->expr()->eq('value', $qb->createNamedParameter($value, $paramType));
 				break;
 			case 'is-not-equal':
@@ -585,6 +599,9 @@ private function getFilterExpression(IQueryBuilder $qb, Column $column, string $
 					$filterExpression = $qb->expr()->neq('value', $qb->createNamedParameter('[' . $this->db->escapeLikeParameter($value) . ']', $paramType));
 					break;
 				}
+				if ($column->getType() === Column::TYPE_RELATION) {
+					return $this->getRelationExclusionFilter($qb, $qb2, $column, (int)$value);
+				}
 				$filterExpression = $qb->expr()->neq('value', $qb->createNamedParameter($value, $paramType));
 				break;
 			case 'is-greater-than':
@@ -649,6 +666,23 @@ private function getFilterExpression(IQueryBuilder $qb, Column $column, string $
 		);
 	}
 
+	/**
+	 * Rows that do not have the given related id among their relation cell values.
+	 */
+	private function getRelationExclusionFilter(IQueryBuilder $qb, IQueryBuilder $qb2, Column $column, int $value): IQueryBuilder {
+		$qb2->andWhere($qb->expr()->eq('value', $qb->createNamedParameter($value, IQueryBuilder::PARAM_INT)));
+
+		return $this->db->getQueryBuilder()
+			->selectAlias('sl3.id', 'row_id')
+			->from('tables_row_sleeves', 'sl3')
+			->where(
+				$qb->expr()->eq('sl3.table_id', $qb->createNamedParameter($column->getTableId(), IQueryBuilder::PARAM_INT))
+			)
+			->andWhere(
+				$qb->expr()->notIn('sl3.id', $qb->createFunction($qb2->getSQL()))
+			);
+	}
+
 	/**
 	 * @throws InternalError
 	 */
@@ -727,7 +761,7 @@ private function parseEntities(IResult $result, array $sleeves): array {
 		}
 
 		$rowValues = [];
-		$keyToColumnId = [];
+		$keyToColumn = [];
 		$keyToRowId = [];
 		$cellMapperCache = [];
 
@@ -752,12 +786,17 @@ private function parseEntities(IResult $result, array $sleeves): array {
 			} else {
 				$rowValues[$compositeKey] = $value;
 			}
-			$keyToColumnId[$compositeKey] = $rowData['column_id'];
+			$keyToColumn[$compositeKey] = $column;
 			$keyToRowId[$compositeKey] = $rowData['row_id'];
 		}
 
 		foreach ($rowValues as $compositeKey => $value) {
-			$rows[$keyToRowId[$compositeKey]]->addCell($keyToColumnId[$compositeKey], $value);
+			$column = $keyToColumn[$compositeKey];
+			$columnType = $column->getType();
+			if ($cellMapperCache[$columnType]->hasMultipleValues() && is_array($value)) {
+				$value = $cellMapperCache[$columnType]->formatAggregatedValues($column, $value);
+			}
+			$rows[$keyToRowId[$compositeKey]]->addCell($column->getId(), $value);
 		}
 
 		return array_values($rows);

lib/Db/RowCellMapperSuper.php

@@ -63,6 +63,16 @@ public function hasMultipleValues(): bool {
 		return false;
 	}
 
+	/**
+	 * Shape aggregated multi-cell values for the API response.
+	 *
+	 * @param list<mixed> $values
+	 * @return mixed
+	 */
+	public function formatAggregatedValues(Column $column, array $values): mixed {
+		return $values;
+	}
+
 	/**
 	 * @throws Exception
 	 */

lib/Db/RowCellRelationMapper.php

@@ -14,23 +14,113 @@
 
 /** @template-extends RowCellMapperSuper<RowCellRelation, int|null, int|null> */
 class RowCellRelationMapper extends RowCellMapperSuper {
+	private const DB_CHUNK_SIZE = 1_000;
+
 	protected string $table = 'tables_row_cells_relation';
 
 	public function __construct(IDBConnection $db) {
 		parent::__construct($db, $this->table, RowCellRelation::class);
 	}
 
 	/**
-	 * @inheritDoc
+	 * Relation values are stored as one cell row per related id (usergroup-style),
+	 * so single- and multi-select columns share the same storage shape.
 	 */
 	public function hasMultipleValues(): bool {
-		return false;
+		return true;
 	}
 
-	/**
-	 * @inheritDoc
-	 */
 	public function getDbParamType() {
 		return IQueryBuilder::PARAM_INT;
 	}
+
+	public function formatRowData(Column $column, array $row) {
+		$value = $row['value'];
+		if ($value === null || $value === '') {
+			return null;
+		}
+		return (int)$value;
+	}
+
+	/**
+	 * @param list<int|null> $values
+	 * @return list<int>|int|null
+	 */
+	public function formatAggregatedValues(Column $column, array $values): mixed {
+		$values = array_values(array_filter($values, static fn ($value) => $value !== null));
+		if (!(bool)($column->getCustomSettingsArray()[Column::RELATION_ALLOW_MULTIPLE] ?? false)) {
+			return $values[0] ?? null;
+		}
+		return $values;
+	}
+
+	public function applyDataToEntity(Column $column, RowCellSuper $cell, $data): void {
+		$cell->setValue($data === null || $data === '' ? null : (int)$data);
+	}
+
+	/**
+	 * Keep only the first related value per row (lowest cell id).
+	 * Used when allowMultiple is turned off on an existing column.
+	 */
+	public function truncateToSingleValuePerRow(int $columnId): void {
+		$qb = $this->db->getQueryBuilder();
+		$qb->select('id', 'row_id')
+			->from($this->table)
+			->where($qb->expr()->eq('column_id', $qb->createNamedParameter($columnId, IQueryBuilder::PARAM_INT)))
+			->orderBy('row_id', 'ASC')
+			->addOrderBy('id', 'ASC');
+
+		$result = $qb->executeQuery();
+		$seenRows = [];
+		$idsToDelete = [];
+		while ($row = $result->fetchAssociative()) {
+			$rowId = (int)$row['row_id'];
+			if (isset($seenRows[$rowId])) {
+				$idsToDelete[] = (int)$row['id'];
+				if (count($idsToDelete) >= self::DB_CHUNK_SIZE) {
+					$this->deleteByIds($idsToDelete);
+					$idsToDelete = [];
+				}
+			} else {
+				$seenRows[$rowId] = true;
+			}
+		}
+		$result->closeCursor();
+
+		if ($idsToDelete !== []) {
+			$this->deleteByIds($idsToDelete);
+		}
+	}
+
+	/**
+	 * @param list<int> $ids
+	 */
+	private function deleteByIds(array $ids): void {
+		$deleteQb = $this->db->getQueryBuilder();
+		$deleteQb->delete($this->table)
+			->where($deleteQb->expr()->in('id', $deleteQb->createNamedParameter($ids, IQueryBuilder::PARAM_INT_ARRAY)));
+		$deleteQb->executeStatement();
+	}
+
+	/**
+	 * Whether any table row has no related value for this column.
+	 */
+	public function hasRowsWithoutValue(int $columnId, int $tableId): bool {
+		$qb = $this->db->getQueryBuilder();
+		$qb->select('sl.id')
+			->from('tables_row_sleeves', 'sl')
+			->leftJoin('sl', $this->table, 'c', $qb->expr()->andX(
+				$qb->expr()->eq('sl.id', 'c.row_id'),
+				$qb->expr()->eq('c.column_id', $qb->createNamedParameter($columnId, IQueryBuilder::PARAM_INT)),
+				$qb->expr()->isNotNull('c.value'),
+			))
+			->where($qb->expr()->eq('sl.table_id', $qb->createNamedParameter($tableId, IQueryBuilder::PARAM_INT)))
+			->andWhere($qb->expr()->isNull('c.id'))
+			->setMaxResults(1);
+
+		$result = $qb->executeQuery();
+		$hasEmpty = $result->fetchOne() !== false;
+		$result->closeCursor();
+		return $hasEmpty;
+	}
 }

lib/Service/ColumnService.php

@@ -13,6 +13,7 @@
 use OCA\Tables\Constants\ColumnType;
 use OCA\Tables\Db\Column;
 use OCA\Tables\Db\ColumnMapper;
+use OCA\Tables\Db\RowCellRelationMapper;
 use OCA\Tables\Db\Table;
 use OCA\Tables\Db\TableMapper;
 use OCA\Tables\Db\View;
@@ -54,6 +55,7 @@ public function __construct(
 		private readonly IL10N $l,
 		private readonly UserHelper $userHelper,
 		private readonly ColumnDtoValidator $columnDtoValidator,
+		private readonly RowCellRelationMapper $rowCellRelationMapper,
 	) {
 		parent::__construct($logger, $userId, $permissionsService);
 	}
@@ -374,6 +376,9 @@ public function update(
 			$this->columnDtoValidator->validate($columnDto);
 			$title = $this->normalizeTitle($columnDto->getTitle(), false);
 
+			$wasMandatory = (bool)$item->getMandatory();
+			$previousAllowMultiple = (bool)($item->getCustomSettingsArray()[Column::RELATION_ALLOW_MULTIPLE] ?? false);
+
 			if ($title !== null) {
 				$item->setTitle($title);
 			}
@@ -425,10 +430,24 @@ public function update(
 			$this->validateCustomSettings($columnDto->getCustomSettings());
 			$item->setCustomSettings($columnDto->getCustomSettings());
 
+			$willBeMandatory = $columnDto->isMandatory() !== null ? (bool)$columnDto->isMandatory() : $wasMandatory;
+			$newAllowMultiple = (bool)($item->getCustomSettingsArray()[Column::RELATION_ALLOW_MULTIPLE] ?? false);
+			if ($item->getType() === Column::TYPE_RELATION && $willBeMandatory && !$wasMandatory) {
+				if ($this->rowCellRelationMapper->hasRowsWithoutValue($item->getId(), $item->getTableId())) {
+					throw new BadRequestError(
+						'Cannot make this relation column mandatory while some rows have no related value.'
+					);
+				}
+			}
+
 			$this->updateMetadata($item, $userId);
 			try {
 				$updatedColumn = $this->mapper->update($item);
 
+				if ($updatedColumn->getType() === Column::TYPE_RELATION && $previousAllowMultiple && !$newAllowMultiple) {
+					$this->rowCellRelationMapper->truncateToSingleValuePerRow($updatedColumn->getId());
+				}
+
 				$this->activityManager->triggerEvent(
 					objectType: ActivityManager::TABLES_OBJECT_COLUMN,
 					object: $updatedColumn,