Add a latest observations endpoint for the nodes

[vforgione]

This is a feature request. It would be helpful to have an endpoint that returns the latest observations for the nodes.

• /nodes/latest to get the latest for all nodes
• /nodes/:vsn/latest to get the latest for a specific node

In this sense, latest would be the latest observation by timestamp for the key {vsn, subsystem, sensor, param}. It may require creating a new table and setting up some triggers.

[vforgione]

There are some changes underway on the design of the data for AoT (I'm part of the design and implementation), so for not it doesn't seem like this is a worthwhile endeavor. The data will change soonish and then I'll have to patch what I've done with this.

I will keep this use case in mind as we design up the next version of Beehive -- this is super useful for multiple use cases internal to AoT as well.

[laconical77]

Actually, as someone who is trying to make use of this AoT data, having a mechanism to read the latest observations would be absolutely fantastic.

I'm trying to set up a system which reads the latest observations for every node in Chicago every 5 minutes, regardless of how long ago the last reading came in. I don't need to see every single change that occurs on every single sensor - just the current snapshot of what is happening at that node. At the moment, I have no way of doing that.

Instead, every 5 minutes I'm sending a query for each node with a timestamp filter asking for the last 5 minutes of data. So I'm asking for far more data than I require because it's the closest method to getting the latest observations that I could come up with. And it isn't foolproof, because there are devices out there with sensors where the data doesn't change for long periods, so when my application starts up it can't guarantee that it has the latest value for each sensor param.

So yeah, +1 for /nodes/:vsn/latest, as it would be very helpful.

[vforgione]

There is a new websocket available to push out the latest observations per node. Take a look at https://api-of-things.plenar.io/ws-demo .