[{"_id":"some_id","temp_f":65.8,"current_observation":{"rain_day_in":0,"soil_moisture_1":10,"soil_moisture_1_day_high":20},"date":"12/23/2021","date_and_time":"2021-12-23T20:34:21"},{"_id":"other doc with missing fields","temp_f":65.8,"current_observation":{"rain_day_in":50},"date":"12/23/2021","date_and_time":"2021-12-23T20:34:21"},{"_id":"other doc with missing nested fields","temp_f":65.8,"date":"12/23/2021","date_and_time":"2021-12-23T20:34:21"}]

db.collection.find({},{"temp_f":1,"rain_day_in":{$ifNull:["$current_observation.rain_day_in",-1000]},"soil_moisture_1":{$ifNull:["$current_observation.soil_moisture_1",-1000]},"soil_moisture_1_day_high":{$ifNull:["$current_observation.soil_moisture_1_day_high",-1000]},"date":1,"_id":0})