feat: add computed relationships

* work for select, mutations, rpc
* overrides detected relationships

test/spec/fixtures/data.sql

@@ -806,3 +806,9 @@ TRUNCATE TABLE unsafe_update_items CASCADE;
 INSERT INTO unsafe_update_items(id, name, observation) VALUES (1, 'item-1', NULL), (2, 'item-2', NULL), (3, 'item-3', NULL);
 TRUNCATE TABLE unsafe_delete_items CASCADE;
 INSERT INTO unsafe_delete_items(id, name, observation) VALUES (1, 'item-1', NULL), (2, 'item-2', NULL), (3, 'item-3', NULL);
+
+TRUNCATE TABLE designers CASCADE;
+INSERT INTO designers(id, name) VALUES (1, 'Sid Meier'), (2, 'Hironobu Sakaguchi');
+
+TRUNCATE TABLE videogames CASCADE;
+INSERT INTO videogames(id, name, designer_id) VALUES (1, 'Civilization I', 1), (2, 'Civilization II', 1), (3, 'Final Fantasy I', 2), (4, 'Final Fantasy II', 2);

test/spec/fixtures/privileges.sql

@@ -197,6 +197,8 @@ GRANT ALL ON TABLE
     , safe_delete_items
     , unsafe_update_items
     , unsafe_delete_items
+    , videogames
+    , designers
 TO postgrest_test_anonymous;
 
 GRANT INSERT ON TABLE insertonly TO postgrest_test_anonymous;

test/spec/fixtures/schema.sql

@@ -2707,3 +2707,49 @@ CREATE OR REPLACE FUNCTION test.load_safeupdate() RETURNS VOID AS $$
 BEGIN
   LOAD 'safeupdate';
 END; $$ LANGUAGE plpgsql SECURITY DEFINER;
+
+CREATE TABLE designers (
+  id int primary key
+, name text
+);
+
+CREATE TABLE videogames (
+  id int primary key
+, name text
+, designer_id int references designers(id)
+);
+
+-- computed relationships
+CREATE FUNCTION test.computed_designers(test.videogames) RETURNS SETOF test.designers AS $$
+  SELECT * FROM test.designers WHERE id = $1.designer_id;
+$$ LANGUAGE sql STABLE ROWS 1;
+
+CREATE FUNCTION test.computed_videogames(test.designers) RETURNS SETOF test.videogames AS $$
+  SELECT * FROM test.videogames WHERE designer_id = $1.id;
+$$ LANGUAGE sql STABLE;
+
+CREATE FUNCTION test.getallvideogames() RETURNS SETOF test.videogames AS $$
+  SELECT * FROM test.videogames;
+$$ LANGUAGE sql STABLE;
+
+CREATE FUNCTION test.getalldesigners() RETURNS SETOF test.designers AS $$
+  SELECT * FROM test.designers;
+$$ LANGUAGE sql STABLE;
+
+-- self join for computed relationships
+CREATE FUNCTION test.child_web_content(test.web_content) RETURNS SETOF test.web_content AS $$
+  SELECT * FROM test.web_content WHERE $1.id = p_web_id;
+$$ LANGUAGE sql STABLE;
+
+CREATE FUNCTION test.parent_web_content(test.web_content) RETURNS SETOF test.web_content AS $$
+  SELECT * FROM test.web_content WHERE $1.p_web_id = id;
+$$ LANGUAGE sql STABLE ROWS 1;
+
+-- overriding computed rels that empty the results
+CREATE FUNCTION test.designers(test.videogames) RETURNS SETOF test.designers AS $$
+  SELECT * FROM test.designers WHERE FALSE;
+$$ LANGUAGE sql STABLE ROWS 1;
+
+CREATE FUNCTION test.videogames(test.designers) RETURNS SETOF test.videogames AS $$
+  SELECT * FROM test.videogames WHERE FALSE;
+$$ LANGUAGE sql STABLE;