Function getFieldsForJoinedLoad

packages/sql/src/AbstractSqlDriver.ts:2490–2699

(
    qb: AnyQueryBuilder<T>,
    meta: EntityMetadata<T>,
    options: FieldsForJoinedLoadOptions<T>,
  )

  }

  protected getFieldsForJoinedLoad<T extends object>(
    qb: AnyQueryBuilder<T>,
    meta: EntityMetadata<T>,
    options: FieldsForJoinedLoadOptions<T>,
  ): InternalField<T>[] {
    const fields: InternalField<T>[] = [];
    const populate = options.populate ?? [];
    const joinedProps = this.joinedProps(meta, populate, options);
    const populateWhereAll =
      (options as Dictionary)?._populateWhere === 'all' || Utils.isEmpty((options as Dictionary)?._populateWhere);

    // Ensure TPT joins are applied early so that _tptAlias is available for join resolution
    // This is needed when populating relations that are inherited from TPT parent entities
    if (!options.parentJoinPath) {
      qb.ensureTPTJoins();
    }

    // root entity is already handled, skip that
    if (options.parentJoinPath) {
      // alias all fields in the primary table
      meta.props
        .filter(prop => this.shouldHaveColumn(meta, prop, populate, options.explicitFields, options.exclude))
        .forEach(prop =>
          fields.push(
            ...this.mapPropToFieldNames(
              qb,
              prop,
              options.parentTableAlias,
              meta,
              options.schema,
              options.explicitFields,
            ),
          ),
        );
    }

    for (const hint of joinedProps) {
      const [propName, ref] = hint.field.split(':', 2) as [EntityKey<T>, string | undefined];
      const prop = meta.properties[propName];

      // Polymorphic to-one: create a LEFT JOIN per target type
      // Skip regular :ref hints — polymorphic to-one already has FK + discriminator in the row
      // But allow filter :ref hints through to create per-target LEFT JOINs with filter checks
      if (
        prop.polymorphic &&
        prop.polymorphTargets?.length &&
        (!ref || hint.filter) &&
        [ReferenceKind.MANY_TO_ONE, ReferenceKind.ONE_TO_ONE].includes(prop.kind)
      ) {
        const basePath = options.parentJoinPath
          ? `${options.parentJoinPath}.${prop.name}`
          : `${meta.name}.${prop.name}`;
        const pathPrefix =
          !options.parentJoinPath && populateWhereAll && !basePath.startsWith('[populate]') ? '[populate]' : '';

        for (const targetMeta of prop.polymorphTargets) {
          const tableAlias = qb.getNextAlias(targetMeta.className);
          const targetPath = `${pathPrefix}${basePath}[${targetMeta.className}]`;