Allow Read Only External Files - Functional Specification


This functionality once implemented allows users to create an external file on a read only device like a CD-ROM and also an external file on a read write medium, but with no write privileges.

User Interface/Usability

The server can open and query from external files with read only access. However the user will get an error when he tries to insert, update or delete a record from such a file. Update and delete are not supported on external files at all.

Error message on Insert:

I/O error for file "file_name".
-Error while trying to write to file.
-Cannot insert because the file is read only or is on a read only medium.

Error message on Delete:

Cannot delete rows from external files.

(Old Error message was "Feature is not supported." "EXT_erase:not yet implemented")

Error message on Update:

Cannot update rows in external files.

(Old Error message was "Feature is not supported." "EXT_modify: not yet implemented")

There are no changes in SQL commands. If the user wants to change the external file from read only to regular read write file, all the attachments to the database using the external file need to detach and then reattach. The server detects the file to be read only at the time and then cache's this information till the last attachment is dropped.

All other functionality like creation of triggers, granting of privileges has not been changed.

Requirements and Constraints

General InterBase requirements apply.

Migration Issues

Error checking in some applications might change we are changing the error messages in case of "delete" and "update" to external files. Further the server will no longer give error messages for read only external files during "select" statements.