Realm Database

PSLab android app provides various new features like accessing data from the sensors that are either inbuilt into the Android phone or common I2C sensors which are connected to the PSLab device through PIC microcontroller. But the problem is that if the user records the data one time he/she may not be able to view that data in the future as there was no way to save that data somewhere. Saved data can be used for school experiments, preparing reports, research purposes etc.

So, now we have integrated Realm database with the Sensor Data Logger module which is a mobile database that can be used to store real-time data in fast and flawless manner. It is a object oriented database so it stores data in the form of objects which makes it usage with object oriented programming language like Java much easier.

In this blog we will demonstrate the process of storing data from one instrument  i.e., Lux Meter which records illuminance with respect to time to understand the process.

First, we have defined a model class “SensorLogged” which contains information pertaining to all one experiment performed by the user. It will have fields like time of start of recording, the time of the end of the recording, date of recording, sensor name etc.

Whenever a user performs an experiment we will store a object of the SensorLogged model class in realm database containing info for that experiment.

public class SensorLogged extends RealmObject {

   private String sensor;
   private long dateTimeStart;
   @PrimaryKey
   private long uniqueRef;
   private long dateTimeEnd;

   public SensorLogged(String sensor) {
       this.sensor = sensor;
   }

   public void setSensor(String sensor) {
       this.sensor = sensor;
   }
   public void setDateTimeStart(long dateTimeStart) {
       this.dateTimeStart = dateTimeStart;
   }
   public void setUniqueRef(long uniqueRef) {
       this.uniqueRef = uniqueRef;
   }
   public void setDateTimeEnd(long dateTimeEnd) {
       this.dateTimeEnd = dateTimeEnd;
   }
}

 

For storing Lux data we have to define a model class “LuxData” which defines all the fields in one reading of experiment.

public class LuxData extends RealmObject {
   private long foreignKey;
   private float lux;
   private long timeElapsed;
   public LuxData() {
   }
   public LuxData(float lux, long timeElapsed) {
       this.lux = lux;
       this.timeElapsed = timeElapsed;
   }
   public long getForeignKey() {
       return foreignKey;
   }
   public void setForeignKey(long foreignKey) {
       this.foreignKey = foreignKey;
   }
}

We will use the object of this class for every reading of one measurement and provide them with the same Foreign Key which will be Primary key uniqueRef of “SensorLogged” model class.

In this way, we can query all the reading belonging to one measurement from the database containing all the LuxData entries.

For storing the data in Realm database we will follow these steps:

1. Begin the Realm transaction.
   

   realm.beginTransaction();

2. Create a object of “SensorLogged” model class for every measurement with the unique Ref as the primary key and store the information like time of start, date of start, sensor name etc. copy it to the Realm Database.
   

   SensorLogged sensorLogged = realm.createObject(SensorLogged.class, uniqueRef);
   sensorLogged.setSensor("Lux Meter");
   sensorLogged.setDateTimeStart(startTime);
   realm.copyToRealm(sensorLogged);

3. For every sensor, reading create a object of LuxData and store the reading in it with the time elapsed and set all the object to same Foreign Key which is same as the Primary key stored in “SensorLogged.class” for this experiment in the previous step and copy it to Realm Database.
   

   for (int i = 0; i < luxRealmData.size(); i++) {
      LuxData tempObject = luxRealmData.get(i);
      tempObject.setForeignKey(uniqueRef);
      realm.copyToRealm(tempObject);
      }

4. Commit the transaction
   

   realm.commitTransaction();

Therefore now the data fetched for each sensor for every experiment is now being saved to the Realm database which we can easily query by using the following code. 

Below code will query all the SensorLogged object in the form of RealmResult<SensorLogged> list which we can use to show to the user the list of all experiments.

results = realm.where(SensorLogged.class)
       .findAll()
       .sort("dateTimeStart", Sort.DESCENDING);

And the code below will query all the LuxData object that contains reading belonging to one experiment whose uniqueRef has been provided as the ForeignKey.

RealmResults<LuxData> results = realm.where(LuxData.class).equalTo("foreignKey",uniqueRef).findAll();

Resources

1. Realm Database official documentation for Java: https://realm.io/docs/java/latest
2. AndroidHive blog on Android Working with Realm Database: https://www.androidhive.info/2016/05/android-working-with-realm-database-replacing-sqlite-core-data