Context description

The context in Altair SmartCore SDK is a data structure holding information hydrated by Altair SmartCore for execution-time use. It allows building expressions and rules with direct access to an event context information.

Scripts are executed when an event is fired and a listener is bound to that event. This event’s information is accessible via the context variable. Different events have different contexts. For example, when a stream is received the context may differ from the one of change status event caused by the absence of a stream. Refer to our Device Inner Status documentation page for more information about how devices may change their status.

For example, for accessing stream’s data content when a data received event is fired in a listener code you can use context.data variable. See the example below to have a snapshot.

Context usage example

This is an example of checking context information by printing "context" content in a script by setting a listener like this one:

If expression: true

Then expression:

If this listener is bound to a device and "listens" to a Data Received Event then a stream sent to that device will send an email will full context information data.

When a stream is sent to the associated device an email will be sent with something like:

Data received & data persisted events context

When a stream is received at Altair SmartCore, no matter if its a data stream or a status stream, there are two events raised in its processing:

• Data Received Event - when the stream is received, BEFORE persistence
• Data Persisted Event - when the stream is persisted in Altair SmartCore DB

In both cases there is a stream involved and its data is stored in the context. This is an example of that context:

The difference between the context in a Data Received Event and a Data Persisted Event is the key id_developer and its corresponding value in the envelope. This is the true id_developer value after stream persistence.

Context content:

Device status change event

When a device changes its inner status, Altair SmartCore raise an event and injects the context to be used in listeners and rules scripts. A status change implies to statuses: one before the change takes place and another when the change is done. For example, a device can be in a "no_data" status and change to "disconnected" or from "OK" to "no_status" and so on.

So, there is 2 status in a "change state" event context:

• context.data.reason.before_status - device’s status BEFORE the event
• context.data.reason.status - device’s status AFTER the event

Please refer to our Device Inner Status documentation page for more details.

This is a full context example. The device test@cariots has changed from ok to disconnected:

Usage example that sends an email with different subjects in function of a devices status change: