Upon a sufficient showing by the attorney for the Commonwealth at an ex parte hearing before a common pleas court judge, the court shall order the district attorney to seal the affidavit or affidavits setting forth probable cause for the issuance of a search warrant until the date of common pleas court arraignment, unless the period is extended by the court for good cause shown. If the case is to be tried in the Philadelphia Municipal Court, the affidavit or affidavits shall be sealed until the time of discovery, unless the period is extended for good cause shown.