PHP + MySQL-一个表保存对多个表中ID的引用

Question

I just would like to know what are the most common approaches to get a table to hold a reference to IDs from multiple tables.

I have a system with modules like customers, suppliers, orders, etc. and I would like to add a "Notes" functionality to all of those modules to be able to add/read notes.

As one customer/supplier/order can have multiple notes, I have chosen the one-to-many relation way and so the notes in their table should refer to the particular item id in a separate column. But as I will refer to IDs from multiple tables, their IDs will be overlapping and I need a way to say in which particular table to search for that ID.

I don't want to create exact the same notes module for each of my modules and here I could concentrate notes in one table. Those notes differ only in the fact, to which module they belong to.

Shall I

• store the particular table name in the notes table? But that name can change later and the system will break
• introduce something like UNIQUE ID or a hash to all of my modules, which would be unique among different tables and store it's id in the notes table?
• create separate notes table for every module and don't worry about code/class/table duplication?

Thanks for your ideas!

Answer 1

We do something similar with notes that can be attached to many objects. Each of our objects has a unique class id (we store each type of object in it's own table), and we store the unique class id + specific object id in the notes table.

We then just have to maintain a lookup of unique class id -> table name. By using the unique class id + object id as the key we ensure that the same id in different tables isn't an issue.