Introduced data manager package

Author: rahul-dhar-e5609

src/distributed/datamanager/db.go

@@ -0,0 +1,18 @@
+package datamanager
+
+import (
+	"database/sql"
+	// for the initialization of the library
+	_ "github.com/lib/pq"
+)
+
+var db *sql.DB
+
+func init() {
+	var err error
+	db, err = sql.Open("postgres",
+		"postres://distributed:distributed@localhost/distributed?sslmode=disable")
+	if err != nil {
+		panic(err.Error())
+	}
+}

src/distributed/datamanager/sensoreader.go

@@ -0,0 +1,61 @@
+package datamanager
+
+import (
+	"distributed/dto"
+	"errors"
+)
+
+// To cache the relationship between the sensor's
+// names and theire IDs in the database so that we
+// need not constantly query the database
+var sensors map[string]int
+
+// SaveReader is a save function that accepts a pointer
+// to a sensor message object and return an error object
+func SaveReader(reading *dto.SensorMessage) error {
+	// checking if already have the ID for the sensor
+	if sensors[reading.Name] == 0 {
+		// not found in cache, fetching relationship
+		getSensors()
+	}
+
+	// checking if current sensor's name is mapped
+	// after querying db
+	if sensors[reading.Name] == 0 {
+		return errors.New("Unable to find the sensor for name '" +
+			reading.Name + "'")
+	}
+
+	// insert reading, of sensor exists
+	q := `
+		INSERT INTO sensor_reading
+		(value, senosr_id, taken_on)
+		VALUES
+		($1, $2, $3)
+	`
+
+	_, err := db.Exec(q, reading.Value, sensors[reading.Name], reading.Timestamp)
+
+	return err
+
+}
+
+func getSensors() {
+	// Re- initializing the map so that
+	// any stale data is discarded
+	sensors = make(map[string]int)
+
+	q := `SELECT id, name FROM sensor`
+
+	// Querying the database
+	rows, _ := db.Query(q)
+
+	for rows.Next() {
+		var id int
+		var name string
+		rows.Scan(&id, &name)
+
+		// updating map
+		sensors[name] = id
+	}
+}