Managing category structures in relational databases
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The document discusses different techniques for managing hierarchical category structures in relational databases. It begins by describing common approaches like adjacency lists and recursive functions, but notes limitations. It then introduces the concept of using nested sets and numbered trees to represent hierarchical data more efficiently. The key benefits outlined are needing fewer queries to read data, better handling of large datasets, and simpler code. Specific functions demonstrated include getting an item's path, descendants, and adding/deleting nodes from the numbered tree structure.
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Managing category structures in relational databases
- 1. Managing category structures in relational databases An introduction to numbered sets Antoine Osanz <antoine@ivt.com.au>
- 2. Parent-Child relationships Very common in web applications Categorise content Manage organisation structures Hierarchical Data
- 3. Hierarchical Data – A tree Home Theatre Projectors Surround Sound Sub Woofers Satellites Speakers
- 4. Common Category Storage “ Adjacency List Model” Stores serial of the parent
- 5. function getPathDetails( $categorySerial , $pathDetails = array ()) { $sql = "SELECT parentSerial, title FROM adjacentList WHERE categorySerial = '" . $categorySerial . "' LIMIT 0,1" ; $result = $this ->dbase->query( $sql ) ; if ( $result ->numRows() == 1 ) { $row = $result ->fetchAssoc( $result ) ; $pathDetails [] = $row [ 'title' ] ; if ( $row [ 'parentSerial' ] > 0) { $pathDetails = $this ->getPathDetails( $row [ 'parentSerial' ], $pathDetails ) ; } return ( $pathDetails ) ; } else { return ( $pathDetails ) ; } } Projectors: getPathDetails(2); [0] => Projectors [1] => Home Theatre Satellites: getPathDetails(6); [0] => Satellites [1] => Speakers [2] => Surround Sound [3] => Home Theatre Path details: Recursive Function
- 6. SELECT level1.title AS lev1Title, level2.title as lev2Title, level3.title as lev3Title, level4.title as lev4Title FROM adjacentList AS level1 LEFT JOIN adjacentList AS level2 ON (level2.parentSerial = level1.categorySerial) LEFT JOIN adjacentList AS level3 ON (level3.parentSerial = level2.categorySerial) LEFT JOIN adjacentList AS level4 ON (level4.parentSerial = level3.categorySerial) WHERE level4.categorySerial = '6'; +--------------+-------------------+--------------+------------+ | lev1Title | lev2Title | lev3Title | lev4Title | +--------------+-------------------+--------------+------------+ | Home Theatre | Surround Sound | Speaker | Satellites | +--------------+-------------------+--------------+------------+ Path details: Self Joins
- 7. Too much effort Recursive functions are confusing Self joins only good depth is known How else can I organise my categories?
- 8. The tree again… Home Theatre Projectors Surround Sound Sub Woofers Satellites Speakers
- 9. Nested and Numbered Sets
- 10. A Numbered Tree Home Theatre Projectors Surround Sound Sub Woofers Satellites Speakers 2 3 4 1 12 5 10 7 9 8 6 11
- 11. Storing a Numbered Tree
- 12. function getPathDetails( $categorySerial , $pathDetails = array ()) { $sql = "SELECT parent.title FROM productCategories AS node, productCategories AS parent WHERE parent.leftNode <= node.leftNode AND parent.rightNode >= node.rightNode AND node.categorySerial = '" . $categorySerial . "' ORDER BY parent.leftNode DESC" ; $result = $this ->dbase->query( $sql ) ; $pathDetails = array () ; while ( $row = $result ->fetchAssoc( $result )) { $pathDetails [] = $row [ 'title' ] ; } return ( $pathDetails ) ; } Projectors: getPathDetails(2); [0] => Projectors [1] => Home Theatre Satellites: getPathDetails(6); [0] => Satellites [1] => Speakers [2] => Surround Sound [3] => Home Theatre Path details: Revisited
- 13. function getDescendants( $categorySerial ) { $sql = "SELECT node.title FROM productCategories AS node, productCategories AS parent WHERE node.leftNode BETWEEN parent.leftNode AND parent.rightNode AND parent.categorySerial = '" . $categorySerial . "' AND node.categorySerial != '". $categorySerial ."' ORDER BY node.leftNode ASC" ; $result = $this ->dbase->query( $sql ) ; $pathDetails = array () ; while ( $row = $result ->fetchAssoc( $result )) { $pathDetails [] = $row [ 'title' ] ; } return ( $pathDetails ) ; } Speakers: getDescendants(5); [0] => Satellites Surround Sound: getDescendants(3); [0] => Speakers [1] => Satellites [2] => Sub Woofers Getting Category Descendants
- 14. START TRANSACTION SELECT @myLeft := leftNode FROM productCategories WHERE categorySerial = '$parentSerial' LIMIT 0,1 UPDATE productCategories SET rightNode = rightNode + 2 WHERE rightNode > @myLeft UPDATE productCategories SET leftNode = leftNode + 2 WHERE leftNode > @myLeft INSERT INTO productCategories SET leftNode = @myLeft + 1, rightNode = @myLeft + 2, title = 'NEW CATEGORY', parentSerial = '$parentSerial' COMMIT Adding Nodes
- 15. START TRANSACTION SELECT @myLeft := IF(MAX(rightNode) IS NULL, 0, MAX(rightNode)) FROM productCategories WHERE parentSerial = '0' LIMIT 0,1 INSERT INTO productCategories SET leftNode = @myLeft + 1, rightNode = @myLeft + 2, title = 'NEW CATEGORY', parentSerial = '$parentSerial' COMMIT Adding Primary Nodes
- 16. START TRANSACTION SELECT @myLeft := leftNode, @myRight := rightNode, @myWidth := rightNode - leftNode + 1 FROM productCategories WHERE categorySerial = '$categorySerial' LIMIT 0,1"; DELETE FROM productCategories WHERE leftNode BETWEEN @myLeft AND @myRight UPDATE productCategories SET rightNode = rightNode - @myWidth WHERE rightNode > @myRight UPDATE productCategories SET leftNode = leftNode - @myWidth WHERE leftNode > @myLeft COMMIT Delete a node & its children
- 17. Less queries to read Better handling of large data sets Simpler/More readable code Why Bother?
- 18. Category Manager Access Permissions Organisation Structures Current Applications
- 19. Thankyou Special thanks to Arjen Lentz, Jonathan Oxer and Mike Hellyer for edumacating me. Questions?