Views on relations

[sigfrido]

Allow user to define views on relations.
We should be able to specify geometry (multilinestring, multipoint or geometrycollection), and which roles to include in the geometry collection.

An example for routes:

CREATE OR REPLACE VIEW osm_views.routes AS
SELECT r.id,
g.geom,
r.tags -> 'ref'::text AS ref,
r.tags -> 'route'::text AS route,
r.tags -> 'from'::text AS inizio,
r.tags -> 'to'::text AS fine,
r.tags -> 'name'::text AS nome,
r.tags -> 'operator'::text AS operator,
r.tags -> 'network'::text AS network,
r.tags
FROM relations r
LEFT JOIN ( SELECT m.relation_id,
st_collect(w.linestring) AS geom
FROM relation_members m
LEFT JOIN ways w ON m.member_type = 'W'::bpchar AND m.member_id = w.id
GROUP BY m.relation_id) g ON r.id = g.relation_id
WHERE (r.tags -> 'type'::text) = 'route'::text
ORDER BY r.tags -> 'ref'::text;