9.6. Large Object: pglarge
- Table of Contents
- open -- opens a large object
- close -- closes the large object
- read -- reads from the large object
- write -- writes to the large object
- seek -- change current position in the large object
- tell -- returns current position in the large object
- unlink -- deletes the large object
- size -- gives the large object size
- export -- saves the large object to file
This object handles all the request concerning a PostgreSQL large object. It embeds and hides all the "recurrent" variables (object oid and connection), exactly in the same way pgobjects do, thus only keeping significant parameters in function calls. It keeps a reference to the pgobject used for its creation, sending requests though with its parameters. Any modification but dereferencing the pgobject will thus affect the pglarge object. Dereferencing the initial pgobject is not a problem since Python will not deallocate it before the large object dereference it. All functions return a generic error message on call error, whatever the exact error was. The error attribute of the object allows to get the exact error message.
pglarge objects define a read-only set of attributes that allow to get some information about it. These attributes are:
- oid
the oid associated with the object
- pgcnx
the pgobject associated with the object
- error
the last warning/error message of the connection
Be careful: In multithreaded environments, error may be modified by another thread using the same pgobject. Remember these object are shared, not duplicated; you should provide some locking to be able if you want to check this. The oid attribute is very interesting because it allow you reuse the oid later, creating the pglarge object with a pgobject getlo() method call.
See also Chapter 2 for more information about the PostgreSQL large object interface.
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