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Robert Treat and I came up with a better way to move
nodes from one branch to another inside of a nested tree:
CREATE or REPLACE FUNCTION move_tree (integer, integer) RETURNS text
AS '
-- Moves part of a nested set tree to another part.
-- Pass in the left of the child (from) and the left of the parent (to)
DECLARE
cleft INTEGER; cright INTEGER;
pleft INTEGER; pright INTEGER;
leftbound INTEGER; rightbound INTEGER;
treeshift INTEGER; cwidth INTEGER;
leftrange INTEGER; rightrange INTEGER;
BEGIN
-- Self-move makes no sense
IF $1 = $2 THEN RETURN ''Cannot move: entries are identical'';
END IF;
SELECT lft, rgt FROM tree WHERE lft = $1 INTO cleft, cright;
SELECT lft, rgt FROM tree WHERE lft = $2 INTO pleft, pright;
-- Make sure the child exists
IF cleft IS NULL THEN RETURN ''No entry found with an left of ''||$1;
END IF;
-- Make sure the parent exists
IF pleft IS NULL THEN RETURN ''No entry found with a left of ''||$2;
END IF;
-- Parent cannot be underneath the child
IF pleft BETWEEN cleft AND cright THEN RETURN ''Cannot move: first entry contains second'';
END IF;
-- Child may already be in the proper place
IF cleft = pleft+1 THEN RETURN ''No changes need to be made'';
END IF;
IF cleft > pleft THEN treeshift := pleft - cleft + 1; leftbound := pleft+1; rightbound := cleft-1; cwidth :=
cright-cleft+1;leftrange := cright; rightrange := pleft;
ELSE treeshift := pleft - cright; leftbound := cright + 1; rightbound := pleft; cwidth := cleft-cright-1;
leftrange := pleft+1; rightrange := cleft;
END IF;
UPDATE tree SET lft = CASE WHEN lft BETWEEN leftbound AND rightbound THEN lft + cwidth WHEN lft
BETWEENcleft AND cright THEN lft + treeshift ELSE lft END, rgt = CASE WHEN rgt BETWEEN
leftboundAND rightbound THEN rgt + cwidth WHEN rgt BETWEEN cleft AND cright THEN rgt + treeshift
ELSErgt END
WHERE lft < leftrange OR rgt > rightrange;
RETURN ''Tree has been moved'';
END;
'
LANGUAGE 'plpgsql';
Greg Sabino Mullane greg@turnstep.com
PGP Key: 0x14964AC8 200211251526
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