Question

I am currently working on restructuring my site’s database. As the schema I have now is not one of the best, I thought it would be useful to hear some suggestions from you.

To start off, my site actually consists of widgets. For each widget I need a table for settings (where each instance of the widget has its user defined settings), a table for common (shared items between instances of the same widget) and userdata (users’ saved data within an instance of a widget).

Until now, I had the following schema, consisting of 2 databases:

• the first database, where I had all site-maintenance tables (e.g. users, widgets installed, logs, notifications, messages etc.) PLUS a table where I joined each widget instance to each user that instanciated it, having assigned a unique ID (so, I have the following columns: user_id, widget_id and unique_id).
• the second database, where I kept all widget-related data. That means, for each widget (unique by its widget_id) I had three tables: [widget_id]_settings, [widget_id]_common and [widget_id]_userdata. In each of these tables, each row held that unique_id of the users’ widget. Actually here was all the users’ data stored within a widget.

To give a short example of how my databases worked:

First database:

• In the users table I have user_id = 1
• In the widgets table I have widget_id = 1
• In the users_widgets table I have user_id = 1, widget_id = 1, unique_id = 1

Second database:

• In the 1_settings I have unique_id = 1, ..., where … represents the user’s widget settings
• In the 1_common I have several rows which represent shared data between instances of the same widget (so, no user specific data here)
• In the 1_userdata I have unique_id = 1, ..., where … represents the user’s widget data. An important notice here is that this table may contain several rows with the same unique_id (e.g. For a tasks widget, a user can have several tasks for a widget instance)

Hope you understood in the rough my database schema.

Now, I want to develop a ‘cleaner’ schema, so it won’t be necessary to have 2 databases and switch each time from one to another in my application. It would be also great if I found a way NOT to dinamically generate tables in the second database (1_settings, 2_settings, … , n_settings).

I will greatly appreciate any effort in suggesting any better way of achieving this. Thank you very much in advance!

EDIT:
Shall I have databases like MongoDB or CouchDB in my mind when restructurating my databases? I mean, for the second database, where it would be better if I didn’t have a fixed schema.
Also, how would traditional SQL’s and NoSQL’s get along on the same site?

Answer 1

A possible schema for the users_widgets table could be:

id | user_id | widget_id

You don’t need the unique_id field in the users_widgets table, unless you want to hide the primary key for some reason. In fact, I would rename this table to something a little more memorable like widget_instances, and use widget_instance_id in the remaining tables of the second database.

One way to handle the second set of tables is by using a metadata style:

widget_instance_settings

id | widget_instance_id | key | value

This would include the userdata, because user_id is related to the widget_instance_id, unless you want to allow a user to create multiple instances of the same widget, and have the same data across all instances for some reason.

widget_common_settings

id | widget_id | key | value

This type of schema can be seen in packages like Elgg.