my-iot/helper.go

package main

import (
	"github.com/aws/aws-sdk-go/aws"
	d "github.com/aws/aws-sdk-go/service/dynamodb"
	"github.com/aws/aws-sdk-go/service/dynamodb/expression"
)

// GetDevices is to get all devices we know
func GetDevices(svc *d.DynamoDB) (*d.ScanOutput, error) {

	proj := expression.NamesList(
		expression.Name("device"),
		expression.Name("name"))

	expr, _ := expression.NewBuilder().WithProjection(proj).Build()

	// Build the query input parameters
	params := &d.ScanInput{
		ExpressionAttributeNames:  expr.Names(),
		ExpressionAttributeValues: expr.Values(),
		ProjectionExpression:      expr.Projection(),
		TableName:                 aws.String("iot-item"),
	}
	return svc.Scan(params)
}

// GetHistory is a query history for any device
func GetHistory(svc *d.DynamoDB, deviceID string, limit int64) (*d.QueryOutput, error) {
	keyCond := expression.Key("device").Equal(expression.Value(deviceID))
	qProj := expression.NamesList(
		expression.Name("device"),
		expression.Name("timestamp"),
		expression.Name("data"))

	qBuilder := expression.NewBuilder().WithKeyCondition(keyCond).WithProjection(qProj)
	qExpression, _ := qBuilder.Build()

	queryInput := &d.QueryInput{
		KeyConditionExpression:    qExpression.KeyCondition(),
		ProjectionExpression:      qExpression.Projection(),
		ExpressionAttributeNames:  qExpression.Names(),
		ExpressionAttributeValues: qExpression.Values(),
		ScanIndexForward:          aws.Bool(false),
		TableName:                 aws.String("iot-logger"),
		Limit:                     aws.Int64(limit),
	}
	return svc.Query(queryInput)
}