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Devices interact with LightDB using the gateways available on the platform. For now, only CoAP is available.

See CoAP Gateway Interface

Example

Let's imagine that we are monitoring environment data using an IoT device. All of the data for our device is going to be saved on LightDB.

Writing/Updating data with POST/PUT​

We can start by saving temperature data on LightDB. On requests to write data, the body can be a JSON/CBOR object or a single value in the following formats:

  • boolean
  • float
  • integer
  • string

Here is a snippet of example code to save a temperature value of 30 Cº at path /env/temp

coap --path /.d/env/temp -m PUT --psk-id deadbeef-id@my-project-id --psk supersecret  --host coap.golioth.io -b "{\"value\":30,\"unit\":\"c\"}" --format json

After the above request and device data saves in LightDB, it will look like this:

{
  "env": {
    "temp": {
      "value" : 30.0,
      "unit" : "c"
    }
  }
}

You can set any data on any path, which allows flexibility throughout the lifetime of the device and connection. Perhaps during initialization we send both temperatur and unit type, but afterwards we only send the temperature value to the specific path. A long as another unit is not written, the first value will persist.

coap --path /.d/env/temp/value -m PUT --psk-id deadbeef-id@my-project-id --psk supersecret  --host coap.golioth.io -b "35" --format json

After this commend, the device state will look like this:

{
  "env": {
    "temp": {
      "value" : 35.0,
      "unit" : "c"
    }
  }
}

You can also write data using our APIs and goliothctl. Taking the enviroment sensing use case, let's say that we want to set a given alert threshold on the device. We can do this way:

$ goliothctl lightdb set [device name] /config/temp -b "{\"min\": 20.0, \"max\": 40.0 }"
note

[device name] should be replace by your device name and wrapped in quotes if spaces are used.

This way the device can also read the /config path and calculate alerts. If an alert condition is met, it can post data to /alert.

coap --path /.d/ -m PUT --psk-id deadbeef-id@my-project-id --psk supersecret  --host coap.golioth.io -b "{\"alert\":{\"temp\":true},\"env\":{\"temp\":{\"value\":45}}}" --format json

The current device state might look like this:

{
  "env": {
    "temp": {
      "value" : 45.0,
      "unit" : "c"
    }
  },
  "alert": {
    "temp": true
  },
  "config": {
    "temp": {
      "min": 20.0,
      "max": 40.0
    }
  }
}

Reading data with GET​

The return value of the CoAP API depends on what is stored on LightDB, which can be any JSON like data type like mentioned on this guide. The value will be encoded depending on the accept header that is set on the request.

So to read the device data, we can issue a GET request like this:

coap --path /.d/env -m GET --psk-id deadbeef-id --psk supersecret --host coap.golioth.io --accept json
Response
payload: Type: Acknowledgement, MID: 64363, Code: Content, Token: 56f991b6703947d7, ContentFormat: application/json
body: {"temp":{"value":45,"unit":"c"}}

And that will return the data like on the previous step:

{
  "temp": {
    "value" : 45.0,
    "unit" : "c"
  }
}

But you can also request a more specific path, like this:

coap --path /.d/env/temp/value -m GET --psk-id deadbeef-id --psk supersecret --host coap.golioth.io --accept json
Response
payload: Type: Acknowledgement, MID: 64363, Code: Content, Token: 56f991b6703947d7, ContentFormat: application/json
body: 45

And in this case, will return just 45.0.

Deleting data with DELETE method​

To remove data, we can send a DELETE request with the path that needs to be cleaned. On our example, let's say that the device has a button to acknowledge the alert state and clean the /alert/temp value.

coap --path /.d/alert/temp -m DELETE --psk-id deadbeef-id --psk supersecret --host coap.golioth.io --accept json

Also, you can do that same acknowledgement via our APIs or goliothctl. Maybe for example, there is a web application that the final user can acknowledge that alert. Using goliothctl you can delete the path with this command:

$ goliothctl lightdb delete [device name] /alert/temp

The final state of the device in this scenario would be like this:

{
  "env:" {
    "temp": {
      "value" : 45.0,
      "unit" : "c"
    }
  },
  "alert": {},
  "config": {
    "temp": {
      "min": 20.0,
      "max": 40.0
    }
  }
}