Using geometry variable in PostgreSQL/PostGIS statements - postgresql

Question

I'm trying to write an UPSERT statement to insert or update a row in a PostgresSQL database containing a geometry column. My input is a KML fragment and the following statement works for me as long as the KML is valid.
UPDATE area SET shape = ST_GeomFromKML('{the KML}') WHERE area_code = '{the area}';
INSERT INTO area(area_code, shape) SELECT '{the area}', ST_GeomFromKML('{the KML}') WHERE NOT EXISTS (SELECT 1 FROM area WHERE area_code = '{0}');
In case it's relevant I am calling this from a C# ASP.NET MVC application using a SqlCommand object, but that shouldn't matter as long as the SQL statement is correct.
The changes I want are to use ST_IsValid and ST_MakeValid to ensure that the column is correct. Unfortunately my recent database experience is mostly SQL Server with a little MySQL and PostgresSQL statements don't appear to handle variables in the same way.
What I would like is for something like:
DECLARE #shape geometry;
SELECT #shape = ST_GeomFromKML('{the KML}');
IF NOT (ST_IsValid(#shape)) SELECT #shape = ST_MakeValid(#shape);
UPDATE area SET shape = #shape WHERE area_code = '{the area}';
INSERT INTO area(area_code, shape) SELECT '{the area}', #shape WHERE NOT EXISTS (SELECT 1 FROM area WHERE area_code = '{0}');
so that I am checking validity and correcting it once in the code. However, even after reading the documentation, I don't understand how to use variables to do this.

Answer 1

In PostgreSQL you need to write a stored procedure in the PL/pgSQL language (assuming that your kml fragment and "the area" are strings):
CREATE FUNCTION myFunc(kml text, zip text) RETURNS void AS $$
DECLARE shp geometry;
BEGIN
shp := ST_GeomFromKML(kml);
IF NOT (ST_IsValid(shp)) THEN
shp := ST_MakeValid(shp);
END IF;
UPDATE area SET shape = shp WHERE area_code = zip;
INSERT INTO area (area_code, shape)
SELECT zip, shp
WHERE NOT EXISTS (SELECT 1 FROM area WHERE area_code = zip);
END;
$$ LANGUAGE plpgsql;
Documentation on PL/pgSQL can be found here.