Question

I’m looking at writing a Django app to help document fairly small IT environments. I’m getting stuck at how best to model the data as the number of attributes per device can vary, even between devices of the same type. For example, a SAN will have 1 or more arrays, and 1 or more volumes. The arrays will then have an attribute of Name, RAID Level, Size, Number of disks, and the volumes will have attributes of Size and Name. Different SANs will have a different number of arrays and volumes.

Same goes for servers, each server could have a different number of disks/partitions, all of which will have attributes of Size, Used space, etc, and this will vary between servers.

Another device type may be a switch, which won’t have arrays or volumes, but will have a number of network ports, some of which may be gigabit, others 10/100, others 10Gigabit, etc.

Further, I would like the ability to add device types in the future without changing the model. A new device type may be a phone system, which will have its own unique attributes which may vary between different phone systems.

I’ve looked into EAV database designs but it seems to get very complicated very quickly, and I’m unclear on whether it’s the best way to go about this. I was thinking something along the lines of the model as shown in the picture.

https://i.stack.imgur.com/ZMnNl.jpg

A bonus would be the ability to create ‘snapshots’ of environments at a particular time, making it possible to view changes to the environment over time. Adding a date column to the attributes table may be a way to solve this.

For the record, this app won’t need to scale very much (at most 1000 devices), so massive scalability isn’t a big concern.

Answer 1

If you are more comfortable with something along the lines of the image you posted, below is a slightly modified version (sorry I can’t upload an image, don’t have enough rep).

+-------------+
| Device Type |
|-------------|
| type        |--------+
+-------------+        |
                       ^
                  +---------------+     +--------------------+     +-----------+
                  | Device        |----<| DeviceAttributeMap |>----| Attribute |
                  |---------------|     |--------------------|     |-----------|
                  | name          |     | Device             |     | name      |
                  | DeviceType    |     | Attribute          |     +-----------+
                  | parent_device |     | value              |
                  | Site          |     +--------------------+
                  +---------------+       
                       v
+-------------+        |
| Site        |        |
|-------------|        |
| location    |--------+
+-------------+

I added a linker table DeviceAttributeMap so you can have more control over an Attribute catalog, allowing queries for devices with the same Attribute but differing values. I also added a field in the Device model named parent_device intended as a self-referential foreign key to capture a relationship between a device’s parent device. You’ll likely want to make this field optional. To make the foreign key parent_device optional in Django set the field’s null and blank attributes to True.