Function EventTriggerAlterTableStart

src/backend/commands/event_trigger.c:1579–1606

* EventTriggerAlterTableStart * Prepare to receive data on an ALTER TABLE command about to be executed * * Note we don't collect the command immediately; instead we keep it in * currentCommand, and only when we're done processing the subcommands we will * add it to the command list. */

 * add it to the command list.
 */
void
EventTriggerAlterTableStart(Node *parsetree)
{
	MemoryContext oldcxt;
	CollectedCommand *command;

	/* ignore if event trigger context not set, or collection disabled */
	if (!currentEventTriggerState ||
		currentEventTriggerState->commandCollectionInhibited)
		return;

	oldcxt = MemoryContextSwitchTo(currentEventTriggerState->cxt);

	command = palloc(sizeof(CollectedCommand));

	command->type = SCT_AlterTable;
	command->in_extension = creating_extension;

	command->d.alterTable.classId = RelationRelationId;
	command->d.alterTable.objectId = InvalidOid;
	command->d.alterTable.subcmds = NIL;
	command->parsetree = copyObject(parsetree);

	command->parent = currentEventTriggerState->currentCommand;
	currentEventTriggerState->currentCommand = command;

	MemoryContextSwitchTo(oldcxt);
}

/*
 * Remember the OID of the object being affected by an ALTER TABLE.