Add dynamic record inspection to PL/PgSQL, useful for generic triggers:

  tval2 := r.(cname);

or

  columns := r.(*);

Titus von Boxberg

doc/src/sgml/plpgsql.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.92 2006/05/30 11:58:05 momjian Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.93 2006/05/30 12:03:12 momjian Exp $ -->
 
 <chapter id="plpgsql"> 
   <title><application>PL/pgSQL</application> - <acronym>SQL</acronym> Procedural Language</title>
@@ -879,6 +879,55 @@ SELECT merge_fields(t.*) FROM table1 t WHERE ... ;
     field in it will draw a run-time error.
    </para>
 
+   <para>
+    To obtain the values of the fields the record is made up of,
+    the record variable can be qualified with the column or field
+    name. This can be done either by literally using the column name
+    or the column name for indexing the record can be taken out of a scalar
+    variable. The syntax for this notation is Record_variable.(IndexVariable).
+    To get information about the column field names of the record, 
+    a special expression exists that returns all column names as an array: 
+    RecordVariable.(*) .
+    Thus, the RECORD can be viewed
+    as an associative array that allows for introspection of it's contents.
+    This feature is especially useful for writing generic triggers that
+    operate on records with unknown structure.
+    Here is an example procedure that shows column names and values
+    of the predefined record NEW in a trigger procedure:
+<programlisting>
+
+CREATE OR REPLACE FUNCTION show_associative_records() RETURNS TRIGGER AS $$
+	DECLARE
+		colname		TEXT;
+		colcontent	TEXT;
+		colnames	TEXT[];
+		coln		INT4;
+		coli		INT4;
+	BEGIN
+-- obtain an array with all field names of the record
+		colnames := NEW.(*);
+		RAISE NOTICE 'All column names of test record: %', colnames;
+-- show field names and contents of record
+		coli := 1;
+		coln := array_upper(colnames,1);
+		RAISE NOTICE 'Number of columns in NEW: %', coln;
+		FOR coli IN 1 .. coln LOOP
+			colname := colnames[coli];
+			colcontent := NEW.(colname);
+			RAISE NOTICE 'column % of NEW: %', quote_ident(colname), quote_literal(colcontent);
+		END LOOP;
+-- Do it with a fixed field name:
+-- will have to know the column name
+		RAISE NOTICE 'column someint of NEW: %', quote_literal(NEW.someint);
+		RETURN NULL;
+	END;
+$$ LANGUAGE plpgsql;
+--CREATE TABLE test_records (someint INT8, somestring TEXT);
+--CREATE TRIGGER tr_test_record BEFORE INSERT ON test_records FOR EACH ROW EXECUTE PROCEDURE show_associative_records();
+
+</programlisting>
+   </para>
+
    <para>
     Note that <literal>RECORD</> is not a true data type, only a placeholder.
     One should also realize that when a <application>PL/pgSQL</application>

src/pl/plpgsql/src/pl_comp.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_comp.c,v 1.104 2006/05/30 11:58:05 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_comp.c,v 1.105 2006/05/30 12:03:13 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -884,7 +884,8 @@ plpgsql_parse_dblword(char *word)
 
 				new = palloc(sizeof(PLpgSQL_recfield));
 				new->dtype = PLPGSQL_DTYPE_RECFIELD;
-				new->fieldname = pstrdup(cp[1]);
+				new->fieldindex.fieldname = pstrdup(cp[1]);
+				new->fieldindex_flag = RECFIELD_USE_FIELDNAME;
 				new->recparentno = ns->itemno;
 
 				plpgsql_adddatum((PLpgSQL_datum *) new);
@@ -990,7 +991,8 @@ plpgsql_parse_tripword(char *word)
 
 				new = palloc(sizeof(PLpgSQL_recfield));
 				new->dtype = PLPGSQL_DTYPE_RECFIELD;
-				new->fieldname = pstrdup(cp[2]);
+				new->fieldindex.fieldname = pstrdup(cp[2]);
+				new->fieldindex_flag = RECFIELD_USE_FIELDNAME;
 				new->recparentno = ns->itemno;
 
 				plpgsql_adddatum((PLpgSQL_datum *) new);
@@ -1438,6 +1440,132 @@ plpgsql_parse_dblwordrowtype(char *word)
 	return T_DTYPE;
 }
 
+/* ----------
+ * plpgsql_parse_recindex
+ * lookup associative index into record
+ * ----------
+ */
+int
+plpgsql_parse_recindex(char *word)
+{
+	PLpgSQL_nsitem *ns1, *ns2;
+	char		*cp[2];
+	int		ret = T_ERROR;
+	char		*fieldvar;
+	int		fl;
+
+	/* Do case conversion and word separation */
+	plpgsql_convert_ident(word, cp, 2);
+	Assert(cp[1] != NULL);
+
+	/* cleanup the "(identifier)" string to "identifier" */
+	fieldvar = cp[1];
+	Assert(*fieldvar == '(');
+	++fieldvar;	/* get rid of ( */
+
+	fl = strlen(fieldvar);
+	Assert(fieldvar[fl-1] == ')');
+	fieldvar[fl-1] = 0; /* get rid of ) */
+
+	/*
+	 * Lookup the first word
+	 */
+	ns1 = plpgsql_ns_lookup(cp[0], NULL);
+	if ( ns1 == NULL )
+	{
+		pfree(cp[0]);
+		pfree(cp[1]);
+		return T_ERROR;
+	}
+
+	ns2 = plpgsql_ns_lookup(fieldvar, NULL);
+	pfree(cp[0]);
+	pfree(cp[1]);
+	if ( ns2 == NULL )	/* name lookup failed */
+		return T_ERROR;
+
+	switch (ns1->itemtype)
+	{
+		case PLPGSQL_NSTYPE_REC:
+			{
+				/*
+				 * First word is a record name, so second word must be an
+				 * variable holding the field name in this record.
+				 */
+				if ( ns2->itemtype == PLPGSQL_NSTYPE_VAR ) {
+					PLpgSQL_recfield *new;
+
+					new = palloc(sizeof(PLpgSQL_recfield));
+					new->dtype = PLPGSQL_DTYPE_RECFIELD;
+					new->fieldindex.indexvar_no = ns2->itemno;
+					new->fieldindex_flag = RECFIELD_USE_INDEX_VAR;
+					new->recparentno = ns1->itemno;
+
+					plpgsql_adddatum((PLpgSQL_datum *) new);
+
+					plpgsql_yylval.scalar = (PLpgSQL_datum *) new;
+					ret =  T_SCALAR;
+				} 
+				break;
+			}
+		default:
+			break;
+	}
+	return ret;
+} 
+
+
+/* ----------
+ * plpgsql_parse_recfieldnames
+ * create fieldnames of a record
+ * ----------
+ */
+int
+plpgsql_parse_recfieldnames(char *word)
+{
+	PLpgSQL_nsitem	*ns1;
+	char		*cp[2];
+	int		ret = T_ERROR;
+
+	/* Do case conversion and word separation */
+	plpgsql_convert_ident(word, cp, 2);
+
+	/*
+	 * Lookup the first word
+	 */
+	ns1 = plpgsql_ns_lookup(cp[0], NULL);
+	if ( ns1 == NULL )
+	{
+		pfree(cp[0]);
+		pfree(cp[1]);
+		return T_ERROR;
+	}
+
+	pfree(cp[0]);
+	pfree(cp[1]);
+
+	switch (ns1->itemtype)
+	{
+		case PLPGSQL_NSTYPE_REC:
+			{
+				PLpgSQL_recfieldproperties *new;
+
+				new = palloc(sizeof(PLpgSQL_recfieldproperties));
+				new->dtype = PLPGSQL_DTYPE_RECFIELDNAMES;
+				new->recparentno = ns1->itemno;
+				new->save_fieldnames = NULL;
+				plpgsql_adddatum((PLpgSQL_datum *) new);
+				plpgsql_yylval.scalar = (PLpgSQL_datum *) new;
+				ret =  T_SCALAR;	/* ??? */
+				break;
+			}
+		default:
+			break;
+	}
+	return ret;
+}
+
+
 /*
  * plpgsql_build_variable - build a datum-array entry of a given
  * datatype

src/pl/plpgsql/src/pl_funcs.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_funcs.c,v 1.50 2006/05/30 11:58:05 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/pl_funcs.c,v 1.51 2006/05/30 12:03:13 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1044,9 +1044,13 @@ plpgsql_dumptree(PLpgSQL_function *func)
 				printf("REC %s\n", ((PLpgSQL_rec *) d)->refname);
 				break;
 			case PLPGSQL_DTYPE_RECFIELD:
-				printf("RECFIELD %-16s of REC %d\n",
-					   ((PLpgSQL_recfield *) d)->fieldname,
-					   ((PLpgSQL_recfield *) d)->recparentno);
+				if ( ((PLpgSQL_recfield *) d)->fieldindex_flag == RECFIELD_USE_FIELDNAME )
+					printf("RECFIELD %-16s of REC %d\n",
+						   ((PLpgSQL_recfield *) d)->fieldindex.fieldname,
+						   ((PLpgSQL_recfield *) d)->recparentno);
+				else
+					printf("RECFIELD Variable of REC %d\n",
+						   ((PLpgSQL_recfield *) d)->recparentno);
 				break;
 			case PLPGSQL_DTYPE_ARRAYELEM:
 				printf("ARRAYELEM of VAR %d subscript ",

src/pl/plpgsql/src/plpgsql.h

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/plpgsql.h,v 1.72 2006/05/30 11:58:05 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/plpgsql.h,v 1.73 2006/05/30 12:03:13 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -52,7 +52,8 @@ enum
 	PLPGSQL_DTYPE_RECFIELD,
 	PLPGSQL_DTYPE_ARRAYELEM,
 	PLPGSQL_DTYPE_EXPR,
-	PLPGSQL_DTYPE_TRIGARG
+	PLPGSQL_DTYPE_TRIGARG,
+	PLPGSQL_DTYPE_RECFIELDNAMES
 };
 
 /* ----------
@@ -251,10 +252,25 @@ typedef struct
 {								/* Field in record */
 	int			dtype;
 	int			rfno;
-	char	   *fieldname;
+	union {
+		char	*fieldname;
+		int	indexvar_no;		/* dno of variable holding index string */
+	} fieldindex;
+	enum {
+		RECFIELD_USE_FIELDNAME,
+		RECFIELD_USE_INDEX_VAR,
+	}	fieldindex_flag;
 	int			recparentno;	/* dno of parent record */
 } PLpgSQL_recfield;
 
+typedef struct
+{								/* Field in record */
+	int			dtype;
+	int			rfno;
+	int			recparentno;			/* dno of parent record */
+	ArrayType *		save_fieldnames;
+} PLpgSQL_recfieldproperties;
+
 
 typedef struct
 {								/* Element of array variable */
@@ -661,6 +677,8 @@ extern int	plpgsql_parse_dblwordtype(char *word);
 extern int	plpgsql_parse_tripwordtype(char *word);
 extern int	plpgsql_parse_wordrowtype(char *word);
 extern int	plpgsql_parse_dblwordrowtype(char *word);
+extern int	plpgsql_parse_recfieldnames(char *word);
+extern int	plpgsql_parse_recindex(char *word);
 extern PLpgSQL_type *plpgsql_parse_datatype(const char *string);
 extern PLpgSQL_type *plpgsql_build_datatype(Oid typeOid, int32 typmod);
 extern PLpgSQL_variable *plpgsql_build_variable(const char *refname, int lineno,

src/pl/plpgsql/src/scan.l

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/scan.l,v 1.47 2006/05/30 11:58:05 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/pl/plpgsql/src/scan.l,v 1.48 2006/05/30 12:03:13 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -222,6 +222,12 @@ dump			{ return O_DUMP;			}
 {param}{space}*\.{space}*{identifier}{space}*%ROWTYPE	{
 	plpgsql_error_lineno = plpgsql_scanner_lineno();
 	return plpgsql_parse_dblwordrowtype(yytext); }
+{identifier}{space}*\.\(\*\)		{
+	plpgsql_error_lineno = plpgsql_scanner_lineno();
+	return plpgsql_parse_recfieldnames(yytext); }
+{identifier}{space}*\.\({identifier}\)		{
+	plpgsql_error_lineno = plpgsql_scanner_lineno();
+	return plpgsql_parse_recindex(yytext); }
 
 {digit}+		{ return T_NUMBER;			}
 

src/test/regress/expected/plpgsql.out

@@ -2725,6 +2725,44 @@ end;
 $$ language plpgsql;
 ERROR:  end label "outer_label" specified for unlabelled block
 CONTEXT:  compile of PL/pgSQL function "end_label4" near line 5
+-- check introspective records
+create table ritest (i INT4, t TEXT);
+insert into ritest (i, t) VALUES (1, 'sometext');
+create function test_record() returns void as $$
+declare
+  cname text;
+  tval  text;
+  ival  int4;
+  tval2 text;
+  ival2 int4;
+  columns text[];
+  r     RECORD;
+begin
+  SELECT INTO r * FROM ritest WHERE i = 1;
+  ival := r.i;
+  tval := r.t;
+  RAISE NOTICE 'ival=%, tval=%', ival, tval;
+  cname := 'i';
+  ival2 := r.(cname);
+  cname :='t';
+  tval2 := r.(cname);
+  RAISE NOTICE 'ival2=%, tval2=%', ival2, tval2;
+  columns := r.(*);
+  RAISE NOTICE 'fieldnames=%', columns;
+  RETURN;
+end;
+$$ language plpgsql;
+select test_record();
+NOTICE:  ival=1, tval=sometext
+NOTICE:  ival2=1, tval2=sometext
+NOTICE:  fieldnames={i,t}
+ test_record 
+-------------
+ 
+ (1 row)
+
+drop table ritest;
+drop function test_record();
 -- using list of scalars in fori and fore stmts
 create function for_vect() returns void as $proc$
 <<lbl>>declare a integer; b varchar; c varchar; r record;

src/test/regress/sql/plpgsql.sql

@@ -2281,6 +2281,38 @@ begin
 end;
 $$ language plpgsql;
 
+-- check introspective records
+create table ritest (i INT4, t TEXT);
+insert into ritest (i, t) VALUES (1, 'sometext');
+create function test_record() returns void as $$
+declare
+  cname text;
+  tval  text;
+  ival  int4;
+  tval2 text;
+  ival2 int4;
+  columns text[];
+  r     RECORD;
+begin
+  SELECT INTO r * FROM ritest WHERE i = 1;
+  ival := r.i;
+  tval := r.t;
+  RAISE NOTICE 'ival=%, tval=%', ival, tval;
+  cname := 'i';
+  ival2 := r.(cname);
+  cname :='t';
+  tval2 := r.(cname);
+  RAISE NOTICE 'ival2=%, tval2=%', ival2, tval2;
+  columns := r.(*);
+  RAISE NOTICE 'fieldnames=%', columns;
+  RETURN;
+end;
+$$ language plpgsql;
+select test_record();
+drop table ritest;
+drop function test_record();
+
+
 -- using list of scalars in fori and fore stmts
 create function for_vect() returns void as $proc$
 <<lbl>>declare a integer; b varchar; c varchar; r record;