Function mapJoinedProp

packages/sql/src/AbstractSqlDriver.ts:804–878

* Maps a single property from a joined result row into the relation pojo. * Handles polymorphic FKs, composite keys, Date parsing, and embedded objects.

(
    relationPojo: EntityData<T>,
    prop: EntityProperty<T>,
    relationAlias: string,
    root: EntityData<T>,
    tz: string | undefined,
    meta: EntityMetadata<T>,
    options?: { deleteFromRoot?: boolean },
  )

   * Handles polymorphic FKs, composite keys, Date parsing, and embedded objects.
   */
  private mapJoinedProp<T extends object>(
    relationPojo: EntityData<T>,
    prop: EntityProperty<T>,
    relationAlias: string,
    root: EntityData<T>,
    tz: string | undefined,
    meta: EntityMetadata<T>,
    options?: { deleteFromRoot?: boolean },
  ): void {
    if (prop.fieldNames.every(name => typeof root[`${relationAlias}__${name}` as EntityKey<T>] === 'undefined')) {
      return;
    }

    if (prop.polymorphic && prop.kind !== ReferenceKind.EMBEDDED) {
      const discriminatorAlias = `${relationAlias}__${prop.fieldNames[0]}` as EntityKey<T>;
      const discriminatorValue = root[discriminatorAlias] as string;
      const pkFieldNames = prop.fieldNames.slice(1);
      const pkValues = pkFieldNames.map(name => root[`${relationAlias}__${name}` as EntityKey<T>]);
      const pkValue = pkValues.length === 1 ? pkValues[0] : pkValues;

      if (discriminatorValue != null && pkValue != null) {
        relationPojo[prop.name] = new PolymorphicRef(discriminatorValue, pkValue) as EntityDataValue<T>;
      } else {
        relationPojo[prop.name] = null;
      }
    } else if (prop.fieldNames.length > 1) {
      // composite keys
      const fk = prop.fieldNames.map(name => root[`${relationAlias}__${name}` as EntityKey<T>]) as Primary<T>[];
      // `mapFlatCompositePrimaryKey` collapses to a scalar when the target PK is a single prop
      // (e.g. a relation referencing a composite unique key on a single-PK target).
      const pk = Utils.mapFlatCompositePrimaryKey(fk, prop);
      const valid = Array.isArray(pk) ? pk.every(val => val != null) : pk != null;
      relationPojo[prop.name] = valid ? (pk as EntityDataValue<T>) : null;
    } else if (prop.runtimeType === 'Date') {
      const alias = `${relationAlias}__${prop.fieldNames[0]}` as EntityKey<T>;
      const value = root[alias] as unknown;

      if (
        tz &&
        tz !== 'local' &&
        typeof value === 'string' &&
        !value.includes('+') &&
        value.lastIndexOf('-') < 11 &&
        !value.endsWith('Z')
      ) {
        relationPojo[prop.name] = this.platform.parseDate(value + tz) as EntityDataValue<T>;
      } else if (['string', 'number'].includes(typeof value)) {
        relationPojo[prop.name] = this.platform.parseDate(value as string) as EntityDataValue<T>;
      } else {
        relationPojo[prop.name] = value as EntityDataValue<T>;
      }
    } else {
      const alias = `${relationAlias}__${prop.fieldNames[0]}` as EntityKey<T>;
      relationPojo[prop.name] = root[alias];

      if (prop.kind === ReferenceKind.EMBEDDED && (prop.object || meta.embeddable)) {
        const item = parseJsonSafe(relationPojo[prop.name]);