54.3. Foreign Data Wrapper Helper Functions
Several helper functions are exported from the core server so that authors of foreign data wrappers can get easy access to attributes of FDW-related objects, such as FDW options. To use any of these functions, you need to include the header file foreign/foreign.h
in your source file. That header also defines the struct types that are returned by these functions.
ForeignDataWrapper * GetForeignDataWrapper(Oid fdwid);
This function returns a ForeignDataWrapper
object for the foreign-data wrapper with the given OID. A ForeignDataWrapper
object contains properties of the FDW (see foreign/foreign.h
for details).
ForeignServer * GetForeignServer(Oid serverid);
This function returns a ForeignServer
object for the foreign server with the given OID. A ForeignServer
object contains properties of the server (see foreign/foreign.h
for details).
UserMapping * GetUserMapping(Oid userid, Oid serverid);
This function returns a UserMapping
object for the user mapping of the given role on the given server. (If there is no mapping for the specific user, it will return the mapping for PUBLIC
, or throw error if there is none.) A UserMapping
object contains properties of the user mapping (see foreign/foreign.h
for details).
ForeignTable * GetForeignTable(Oid relid);
This function returns a ForeignTable
object for the foreign table with the given OID. A ForeignTable
object contains properties of the foreign table (see foreign/foreign.h
for details).
List * GetForeignColumnOptions(Oid relid, AttrNumber attnum);
This function returns the per-column FDW options for the column with the given foreign table OID and attribute number, in the form of a list of DefElem
. NIL is returned if the column has no options.
Some object types have name-based lookup functions in addition to the OID-based ones:
ForeignDataWrapper * GetForeignDataWrapperByName(const char *name, bool missing_ok);
This function returns a ForeignDataWrapper
object for the foreign-data wrapper with the given name. If the wrapper is not found, return NULL if missing_ok is true, otherwise raise an error.
ForeignServer * GetForeignServerByName(const char *name, bool missing_ok);
This function returns a ForeignServer
object for the foreign server with the given name. If the server is not found, return NULL if missing_ok is true, otherwise raise an error.