MongoDB IoT Patterns

Setup

Create a free M0 MongoDB Atlas cluster in the cloud provider of your choice.

Install Python 3 and the following packages pymongo, dnspython.

Copy connection_string.txt.template to connection_string.txt and paste in the Atlas connection string as documented here

You can then run the queries below and view the results using the community edition of MongoDB Compass

Queries

Find any bucket document with a measurement where pressure >= 1040

db.schema_demo5.find({'measurements.pressure' : { '$gte' : 1040 }})

Find any bucket document with a measurement where pressure >= 1040 and filter the sub measurements to only include those readings

db.schema_demo5.aggregate(
    [
      {
        $match: { "measurements.pressure" : { $gte : 1040 } }
      }, 
      {
        $project: 
          {
            measurement : 
              {
                  $filter : 
                  {
                    input : "$measurements",
                    as : 'item',
                    cond : { $gte : ['$$item.pressure', 1040] }
                  }
              },
            sensor_id : 1,
            count : 1
          }
        }
      ]
)

Reactive code

Use an Atlas Trigger to respond to a particular document update

Use a match expression like

{ "fullDocument.measurements.pressure" : { "$gte" : 1050 } }

And a function like

exports = function(changeEvent) {

  console.log(changeEvent);
  
  var collection = context.services.get("iot-demo").db("iot").collection("alerts");
  var alert_message = { 'message' : 'Pressure has gone above value', 'm' : changeEvent.fullDocument };
  collection.insertOne(alert_message);
  
};