Question

I am planning on using a recursive table in my data model so that I can support an undetermined number of children that can live under a parent. My example is a Table of Contents where I don’t know how deep my subsections will be under a chapter.

The issue I am stumbling over is what techniques do folks use to populate there DB once they have defined a recursive table? By that I mean if I have a list of items that refer to a chapter -> Section -> Subsection…when I load the Chapter, Section, and Subsection into the model I need to identity the lowest level of the hierarchy and assign that value to the Item I am loading (Foreign Key – I would assume) so that I can always get all of the info about that item.

So for example:

Item: 2A-GHI: Chapter: 2 Section: A SubSection: GHI

If I have my data loaded like

ID|TOCID|TOC_VALUE|PARENT_ID  
1|Chapter|2|-1  
2|Section|A|1  
3|SubSection|GHI|2    

How do i tie the item to GHI so that I can set the FK to the Recursive Table for that Item?
Do you use all three values as a Key and set that as another column in the table so that on load you can identity the lowest level?

Like So:

ID|TOCID|TOC_VALUE|PARENT_ID|Key  
1|Chapter|2|-1|2  
2|Section|A|1|2_A  
3|SubSection|GHI|2|2_A_GHI

I can load the recursive table and I am using a CTE to recurse the data, but I am not sure what the best method is to load the recursive data and tie that data into the model so that my item has a FK to the Table of Contents data.

Answer 1

You need a column for the row’s parent ID.

ID|TOCID|TOC_VALUE|parent 
1|Chapter|2|0
2|Section|A|1 
3|SubSection|GHI|2

a parentID of 0 or null means it’s a root (chapter) node