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

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tval2 := r.(cname);

or

  columns := r.(*);

Titus von Boxberg
This commit is contained in:
Bruce Momjian
2006-05-30 12:03:13 +00:00
parent 88ba64d396
commit 38c7700f56
8 changed files with 472 additions and 38 deletions
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51
doc/src/sgml/plpgsql.sgml
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@ -1,4 +1,4 @@
<!-- $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>