SQL sub-queries for -say- dijkstra_sp

Question

I want to combine the following 3 commands (and eventually other ones such as functions from matching.sql right after...):

routing=> select source as s from ways where gid=10213;
  s   
------
 8217
(1 row)

routing=> select target as t from ways where gid=64552;
   t   
-------
 44926
(1 row)

routing=> insert into test(the_geom) select ST_UNION(the_geom) from dijkstra_sp('ways', 8217, 44726);
INSERT 0 1

So I tried many things that look like

WITH depart AS (SELECT source AS s FROM ways WHERE gid=10213), 
    arrivee AS (SELECT target as t FROM ways where gid=64552) 
INSERT INTO test(the_geom) SELECT ST_UNION(the_geom) 
FROM dijkstra_sp('ways', depart.s, arrivee.t);

but any of my experiments worked; any idea someone, please??

Edit: Thanks to dkastl, I wrote the following, certainly not optimized but still working one-line function to get a path from coordinates :

INSERT INTO test(the_geom) SELECT ST_UNION(the_geom) 
    FROM dijkstra_sp('ways', 
        (SELECT source from ways 
where distance(the_geom, geometryFromText('POINT(5.697 45.27433)', 4326)) = 
        (select min(distance(the_geom, GeometryFromText('POINT(5.697 45.27433)', 4326))) as dist from ways where the_geom && setsrid('BOX3D(0 30, 12 60)'::box3d, 4326))), 
        (SELECT source 
            from ways 
                where distance(the_geom, GeometryFromText('POINT(5.05169 45.0482)', 4326)) 
                = (select min(distance(the_geom, GeometryFromText('POINT(5.05169 45.0482)', 4326))) as dist 
                        from ways 
                        where the_geom && setsrid('BOX3D(0 30, 12 60)'::box3d, 4326)
                    )
         )
 );

Thanks!

Answer 1

This should work:

INSERT INTO test(the_geom) SELECT ST_UNION(the_geom) 
    FROM dijkstra_sp('ways', 
        (SELECT source FROM ways WHERE gid=10213)::integer, 
        (SELECT target FROM ways WHERE gid=64552)::integer
    );