Implementing VelocityDB aggregation queries using Java
To implement aggregate queries for VelocityDB using Java, it is necessary to first add dependencies for VelocityDB, with specific Maven coordinates as follows:
<dependency>
<groupId>com.velocitydb</groupId>
<artifactId>VelocityDB</artifactId>
Version Number
</dependency>
Next, we can implement various data aggregation queries through the query interface provided by VelocityDB. The following are several commonly used examples of aggregation queries:
**Example 1: Calculating the Sum of a Property**
import com.velocitydb.Session;
import com.velocitydb.database.AggregateFunction;
import com.velocitydb.Database;
import com.velocitydb.query.ElementQuery;
import com.velocitydb.query.ScalarAggregator;
public class VelocityDBAggregatesDemo {
public static void main(String[] args) {
Try (Session session=new Session ("Database Path")){
Database db = session.getDatabase();
ElementQuery query = db.query();
Query. setType (Person. class)// Person is the object to query
Query. addToFields ("age")// Attribute to calculate total
ScalarAggregator aggregator = query.aggregate();
Aggregator. addFunction (AggregateFunction. SUM, "age")// SUM represents summation, where we want to sum the age attribute
double sum = aggregator.execute();
System. out. println ("Age total:"+sum);
} catch (Exception e) {
e.printStackTrace();
}
}
}
**Example 2: Calculating the average value of a certain attribute**
import com.velocitydb.Session;
import com.velocitydb.database.AggregateFunction;
import com.velocitydb.Database;
import com.velocitydb.query.ElementQuery;
import com.velocitydb.query.ScalarAggregator;
public class VelocityDBAggregatesDemo {
public static void main(String[] args) {
Try (Session session=new Session ("Database Path")){
Database db = session.getDatabase();
ElementQuery query = db.query();
Query. setType (Person. class)// Person is the object to query
Query. addToFields ("age")// The attribute to calculate the average
ScalarAggregator aggregator = query.aggregate();
Aggregator. addFunction (AggregateFunction. AVERAGE, "age")// AVERAGE represents the average value, where the age attribute needs to be averaged
double average = aggregator.execute();
System. out. println ("Age average:"+average);
} catch (Exception e) {
e.printStackTrace();
}
}
}
**Example 3: Calculating the maximum value of a certain attribute**
import com.velocitydb.Session;
import com.velocitydb.database.AggregateFunction;
import com.velocitydb.Database;
import com.velocitydb.query.ElementQuery;
import com.velocitydb.query.ScalarAggregator;
public class VelocityDBAggregatesDemo {
public static void main(String[] args) {
Try (Session session=new Session ("Database Path")){
Database db = session.getDatabase();
ElementQuery query = db.query();
Query. setType (Person. class)// Person is the object to query
Query. addToFields ("age")// The attribute to calculate the maximum value for
ScalarAggregator aggregator = query.aggregate();
Aggregator. addFunction (AggregateFunction. MAX, "age")// MAX represents the maximum value, where the age attribute needs to be maximized
double max = aggregator.execute();
System. out. println ("Age max:"+max);
} catch (Exception e) {
e.printStackTrace();
}
}
}
The above example shows aggregation query operations for calculating total, average, and maximum values. According to specific needs, other aggregation functions and operators provided by VelocityDB can be used for more complex queries.
