Function applyUnionWhere

packages/sql/src/AbstractSqlDriver.ts:3140–3195

* Builds a UNION ALL (or UNION) subquery from `unionWhere` branches and merges it * into the main WHERE as `pk IN (branch_1 UNION ALL branch_2 ...)`. * Each branch is planned independently by the database, enabling per-table index usage.

(
    meta: EntityMetadata<T>,
    where: ObjectQuery<T>,
    options: FindOptions<T, any, any, any> | CountOptions<T> | NativeInsertUpdateOptions<T> | DeleteOptions<T>,
    forDml = false,
  )

   * Each branch is planned independently by the database, enabling per-table index usage.
   */
  protected async applyUnionWhere<T extends object>(
    meta: EntityMetadata<T>,
    where: ObjectQuery<T>,
    options: FindOptions<T, any, any, any> | CountOptions<T> | NativeInsertUpdateOptions<T> | DeleteOptions<T>,
    forDml = false,
  ): Promise<ObjectQuery<T>> {
    const unionWhere = (options as FindOptions<T>).unionWhere!;
    const strategy = (options as FindOptions<T>).unionWhereStrategy ?? 'union-all';
    const schema = this.getSchemaName(meta, options);
    const connectionType = this.resolveConnectionType({
      ctx: options.ctx,
      connectionType: (options as FindOptions<T>).connectionType,
    });

    const branchQbs: QueryBuilder<any>[] = [];

    for (const branch of unionWhere) {
      const qb = this.createQueryBuilder<T>(
        meta.class,
        options.ctx,
        connectionType,
        false,
        (options as FindOptions<T>).logging,
      ).withSchema(schema);

      const pkFields = meta.primaryKeys.map(pk => {
        const prop = meta.properties[pk];
        return `${qb.alias}.${prop.fieldNames[0]}`;
      });

      qb.select(pkFields as any).where(branch as any);

      if (options.em) {
        await qb.applyJoinedFilters(options.em, options.filters);
      }

      branchQbs.push(qb);
    }

    const [first, ...rest] = branchQbs;
    const unionQb = strategy === 'union' ? first.union(...rest) : first.unionAll(...rest);
    const pkHash = Utils.getPrimaryKeyHash(meta.primaryKeys);

    // MySQL does not allow referencing the target table in a subquery
    // for UPDATE/DELETE, so we wrap the union in a derived table.
    if (forDml) {
      const { sql, params } = unionQb.toQuery();
      return {
        $and: [where, { [pkHash]: { $in: raw(`select * from (${sql}) as __u`, params) } }],
      } as ObjectQuery<T>;
    }

    return {
      $and: [where, { [pkHash]: { $in: unionQb.toRaw() } }],
    } as ObjectQuery<T>;
  }

  protected buildOrderBy<T extends object>(