116 lines
4.3 KiB
PL/PgSQL
116 lines
4.3 KiB
PL/PgSQL
CREATE OR REPLACE FUNCTION add_edge(parent_id uuid, child_id uuid)
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/* Adds an edge between ``parent`` and ``child``.
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Designed to work with Directed Acyclic Graphs (DAG)
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(or said in another way, trees with multiple parents without cycles).
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This method will raise an exception if:
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- Parent is the same as child.
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- Child contains the parent.
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- Edge parent - child already exists.
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Influenced by:
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- https://www.codeproject.com/Articles/22824/A-Model-to-Represent-Directed-Acyclic-Graphs-DAG
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- http://patshaughnessy.net/2017/12/12/installing-the-postgres-ltree-extension
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- https://en.wikipedia.org/wiki/Directed_acyclic_graph
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*/
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RETURNS void AS
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$$
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DECLARE
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parent text := replace(CAST(parent_id as text), '-', '_');
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child text := replace(CAST(child_id as text), '-', '_');
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BEGIN
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if parent = child
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then
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raise exception 'Cannot create edge: the parent is the same as the child.';
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end if;
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if EXISTS(
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SELECT 1
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FROM path
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where path.path ~ CAST('*.' || child || '.*.' || parent || '.*' as lquery)
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)
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then
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raise exception 'Cannot create edge: child already contains parent.';
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end if;
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-- We have two subgraphs: the parent subgraph that goes from the parent to the root,
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-- and the child subgraph, going from the child (which is the root of this subgraph)
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-- to all the leafs.
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-- We do the cartesian product from all the paths of the parent subgraph that end in the parent
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-- WITH all the paths that start from the child that end to its leafs.
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insert into path (lot_id, path) (
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select distinct lot_id, fp.path || subpath(path.path, index(path.path, text2ltree(child)))
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from path,
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(select path.path from path where path.path ~ CAST('*.' || parent AS lquery)) as fp
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where path.path ~ CAST('*.' || child || '.*' AS lquery)
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);
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-- Cleanup: old paths that start with the child (that where used above in the cartesian product)
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-- have became a subset of the result of the cartesian product, thus being redundant.
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delete from path where path.path ~ CAST(child || '.*' AS lquery);
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END
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$$
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LANGUAGE plpgsql;
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CREATE OR REPLACE FUNCTION delete_edge(parent_id uuid, child_id uuid)
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/* Deletes an edge between ``parent`` and ``child``.
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Designed to work with DAG (See ``add_edge`` function).
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This method will raise an exception if the relationship does not
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exist.
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*/
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RETURNS void AS
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$$
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DECLARE
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parent text := replace(CAST(parent_id as text), '-', '_');
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child text := replace(CAST(child_id as text), '-', '_');
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number int;
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BEGIN
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-- to delete we remove from the path of the descendants of the child
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-- (and the child) any ancestor coming from this edge.
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-- When we added the edge we did a cartesian product. When removing
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-- this part of the path we will have duplicate paths.
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-- don't check uniqueness for path key until we delete duplicates
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SET CONSTRAINTS path_unique DEFERRED;
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-- remove everything above the child lot_id in the path
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-- this creates duplicates on path and lot_id
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update path
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set path = subpath(path, index(path, text2ltree(child)))
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where path ~ CAST('*.' || parent || '.' || child || '.*' AS lquery);
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-- remove duplicates
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-- we need an id field exclusively for this operation
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-- from https://wiki.postgresql.org/wiki/Deleting_duplicates
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DELETE
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FROM path
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WHERE id IN (SELECT id
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FROM (SELECT id, ROW_NUMBER() OVER (partition BY lot_id, path) AS rnum
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FROM path) t
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WHERE t.rnum > 1);
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-- re-activate uniqueness check and perform check
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-- todo we should put this in a kind-of finally clause
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SET CONSTRAINTS path_unique IMMEDIATE;
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-- After the update the one of the paths of the child will be
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-- containing only the child.
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-- This can only be when the child has no parent at all.
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-- In case the child has more than one parent, remove this path
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-- (note that we want it to remove it too from descendants of this
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-- child, ex. 'child_id'.'desc1')
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select COUNT(1) into number from path where lot_id = child_id;
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IF number > 1
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THEN
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delete from path where path <@ text2ltree(child);
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end if;
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END
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$$
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LANGUAGE plpgsql;
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