add structure

lib/vo/log.dart

@@ -0,0 +1,24 @@
+import 'package:cloud_firestore/cloud_firestore.dart';
+
+class Log {
+  DateTime activeTime;
+  String deviceID;
+  String deviceName;
+
+  Log({this.activeTime, this.deviceID, this.deviceName});
+
+  factory Log.fromMap(Map<String, dynamic> map, String docID) {
+    var activeTime = (map['active_time'] as Timestamp);
+
+    return Log(
+      activeTime: activeTime == null ? null : activeTime.toDate(),
+      deviceID: map['device_id'],
+      deviceName: map['device_name'],
+    );
+  }
+
+  @override
+  String toString() {
+    return 'Log{activeTime: $activeTime, deviceID: $deviceID, deviceName: $deviceName}';
+  }
+}