Manually Building a Tree in CakePHP

Question

I'm currently working on building an application in CakePHP. There's a quite extensive existing data set that's conceptually a tree, but wasn't previously stored as one. What I mean by that, is there's no real relationship defined in the data.

The problem I'm having is getting it to work correctly with the CakePHP tree behaviour. Because I have to set all the values on existing data - as opposed to Cake setting up the structure as elements are inserted - I need to understand how the lft/rght values work.

So, I guess the question is:

How does the structure data work, specifically the lft/rght values? How do I set it up so that the data comes out rationally, without inserting them one at a time? It's a 2 level tree, with Sections and sub-sections.

Thanks for the help

Answer 1

The MPTT tree logic is rather simple and well explained here. In summary, every entry has a left and a right value. Every entry whos left/right values are within another entries left-right range are a descendent of that (latter) element. E.g. the LCD node (5/6) is within the range of its parent node, Televisions (2-9).

To build the lft/rght values for a "new" tree just set all the parent_ids properly and run $this->Model->recover() on it. Cake will calculate the lft/rght values for you.

Answer 2

wow. thank you! I thought I would manually create my hundreds categories and subcategories again.