Hierarchical database example how to#

For each of these children, the function should retrieve and display all the child nodes of that child. This function will have to start at the root node - the node with no parent - and should then display all children of that node. Now that weвЂ™ve inserted our tree in the database, itвЂ™s time to write a display function. Of course, in a real database, youвЂ™d use the numerical id of each node. For simplicity, IвЂ™ve used the вЂtitleвЂ™ value to identify each node. The root node, вЂFoodвЂ™, doesnвЂ™t have a parent value.

We can see that вЂPearвЂ™ is a child of вЂGreenвЂ™, which is a child of вЂFruitвЂ™ and so on. In our food store, the table for an adjacency list looks like this:ДЄs you can see, in the adjacency list method, you save the вЂparentвЂ™ of each node. ItвЂ™s an elegant approach because youвЂ™ll need just one, simple function to iterate through your tree. The first, and most elegant, approach weвЂ™ll try is called the вЂadjacency list modelвЂ™ or the вЂrecursion methodвЂ™. You can probably easily translate them to your own language of choice. Because I use that language myself, and many other people use or know that language too, I chose to write the examples in PHP.

Hierarchical database example how to#

This article contains a number of code examples that show how to save and retrieve data. This food store organizes its food by category, by colour and by type. IвЂ™ll use the tree from a fictional online food store as an example. In this article, weвЂ™ll explore these two methods of saving hierarchical data. There are two major approaches: the adjacency list model, and the modified preorder tree traversal algorithm. Storing trees is a common problem, with multiple solutions. YouвЂ™ll have to find a way to translate the hierarchy in a flat file. And, unless youвЂ™re using a XML-like database, tables arenвЂ™t hierarchical theyвЂ™re just a flat list. Whether you want to build your own forum, publish the messages from a mailing list on your Website, or write your own cms: there will be a moment that youвЂ™ll want to store hierarchical data in a database. If youвЂ™re keen to learn more about mastering database management, you may find this recent article on MySQL of great interest. This article was written in 2003 and remains one of our most popular posts.