1 /*
2  *	PostgreSQL definitions for managed Large Objects.
3  *
4  *	contrib/lo/lo.c
5  *
6  */
7 
8 #include "postgres.h"
9 
10 #include "commands/trigger.h"
11 #include "executor/spi.h"
12 #include "utils/builtins.h"
13 #include "utils/rel.h"
14 
15 PG_MODULE_MAGIC;
16 
17 
18 /*
19  * This is the trigger that protects us from orphaned large objects
20  */
21 PG_FUNCTION_INFO_V1(lo_manage);
22 
23 Datum
24 lo_manage(PG_FUNCTION_ARGS)
25 {
26 	TriggerData *trigdata = (TriggerData *) fcinfo->context;
27 	int			attnum;			/* attribute number to monitor	*/
28 	char	  **args;			/* Args containing attr name	*/
29 	TupleDesc	tupdesc;		/* Tuple Descriptor				*/
30 	HeapTuple	rettuple;		/* Tuple to be returned			*/
31 	bool		isdelete;		/* are we deleting?				*/
32 	HeapTuple	newtuple;		/* The new value for tuple		*/
33 	HeapTuple	trigtuple;		/* The original value of tuple	*/
34 
35 	if (!CALLED_AS_TRIGGER(fcinfo)) /* internal error */
36 		elog(ERROR, "lo_manage: not fired by trigger manager");
37 
38 	if (!TRIGGER_FIRED_FOR_ROW(trigdata->tg_event)) /* internal error */
39 		elog(ERROR, "%s: must be fired for row",
40 			 trigdata->tg_trigger->tgname);
41 
42 	/*
43 	 * Fetch some values from trigdata
44 	 */
45 	newtuple = trigdata->tg_newtuple;
46 	trigtuple = trigdata->tg_trigtuple;
47 	tupdesc = trigdata->tg_relation->rd_att;
48 	args = trigdata->tg_trigger->tgargs;
49 
50 	if (args == NULL)			/* internal error */
51 		elog(ERROR, "%s: no column name provided in the trigger definition",
52 			 trigdata->tg_trigger->tgname);
53 
54 	/* tuple to return to Executor */
55 	if (TRIGGER_FIRED_BY_UPDATE(trigdata->tg_event))
56 		rettuple = newtuple;
57 	else
58 		rettuple = trigtuple;
59 
60 	/* Are we deleting the row? */
61 	isdelete = TRIGGER_FIRED_BY_DELETE(trigdata->tg_event);
62 
63 	/* Get the column we're interested in */
64 	attnum = SPI_fnumber(tupdesc, args[0]);
65 
66 	if (attnum <= 0)
67 		elog(ERROR, "%s: column \"%s\" does not exist",
68 			 trigdata->tg_trigger->tgname, args[0]);
69 
70 	/*
71 	 * Handle updates
72 	 *
73 	 * Here, if the value of the monitored attribute changes, then the large
74 	 * object associated with the original value is unlinked.
75 	 */
76 	if (newtuple != NULL &&
77 		bms_is_member(attnum - FirstLowInvalidHeapAttributeNumber, trigdata->tg_updatedcols))
78 	{
79 		char	   *orig = SPI_getvalue(trigtuple, tupdesc, attnum);
80 		char	   *newv = SPI_getvalue(newtuple, tupdesc, attnum);
81 
82 		if (orig != NULL && (newv == NULL || strcmp(orig, newv) != 0))
83 			DirectFunctionCall1(be_lo_unlink,
84 								ObjectIdGetDatum(atooid(orig)));
85 
86 		if (newv)
87 			pfree(newv);
88 		if (orig)
89 			pfree(orig);
90 	}
91 
92 	/*
93 	 * Handle deleting of rows
94 	 *
95 	 * Here, we unlink the large object associated with the managed attribute
96 	 */
97 	if (isdelete)
98 	{
99 		char	   *orig = SPI_getvalue(trigtuple, tupdesc, attnum);
100 
101 		if (orig != NULL)
102 		{
103 			DirectFunctionCall1(be_lo_unlink,
104 								ObjectIdGetDatum(atooid(orig)));
105 
106 			pfree(orig);
107 		}
108 	}
109 
110 	return PointerGetDatum(rettuple);
111 }
112