Implementing eXtremeDB aggregation queries using Java
EXtremeDB is a high-performance embedded database system, with its Java API providing rich aggregation query functionality. The following will introduce how to use Java to implement various aggregation queries for eXtremeDB, and provide corresponding code examples.
1. Mean Query
The mean query is used to calculate the average value of a field. Assuming there is a 'Person' class that contains the field 'age', we need to calculate the average age of all people.
import com.mcobject.example.Person;
import com.mcobject.query.MCQuery;
import com.mcobject.query.MCAggregate;
//Create Query Object
MCQuery<Person> query = new MCQuery<>(Person.class);
//Create an aggregation object and calculate the average value of the age field
MCAggregate<Double> meanAggregate = MCAggregate.mean("age");
//Execute Query
double meanAge = query.aggregate(meanAggregate);
//Print Results
System.out.println("Mean age: " + meanAge);
2. Max Query
The maximum value query is used to find the maximum value of a field. Assuming there is a 'Product' class that contains the field 'price', we need to find the highest product price.
import com.mcobject.example.Product;
import com.mcobject.query.MCQuery;
import com.mcobject.query.MCAggregate;
//Create Query Object
MCQuery<Product> query = new MCQuery<>(Product.class);
//Create an aggregation object and find the maximum value of the price field
MCAggregate<Double> maxAggregate = MCAggregate.max("price");
//Execute Query
double maxPrice = query.aggregate(maxAggregate);
//Print Results
System.out.println("Max price: " + maxPrice);
3. Min Query
The minimum value query is used to find the minimum value of a field. Assuming there is a 'Product' class that contains the field 'price', we need to find the lowest product price.
import com.mcobject.example.Product;
import com.mcobject.query.MCQuery;
import com.mcobject.query.MCAggregate;
//Create Query Object
MCQuery<Product> query = new MCQuery<>(Product.class);
//Create an aggregation object and find the minimum value of the price field
MCAggregate<Double> minAggregate = MCAggregate.min("price");
//Execute Query
double minPrice = query.aggregate(minAggregate);
//Print Results
System.out.println("Min price: " + minPrice);
4. Sum Query
A sum query is used to calculate the sum of a certain field. Assuming there is an 'Order' class that contains the field 'totalAmount', we need to calculate the total amount of all orders.
import com.mcobject.example.Order;
import com.mcobject.query.MCQuery;
import com.mcobject.query.MCAggregate;
//Create Query Object
MCQuery<Order> query = new MCQuery<>(Order.class);
//Create an aggregation object and calculate the total of the totalAmount field
MCAggregate<Double> sumAggregate = MCAggregate.sum("totalAmount");
//Execute Query
double totalAmount = query.aggregate(sumAggregate);
//Print Results
System.out.println("Total amount: " + totalAmount);
The above is an example of using Java to implement various aggregation queries in eXtremeDB. In the code, we used the 'MCQuery' class and the 'MCAggregate' class provided by the Java API of eXtremeDB to implement the aggregation query function. The specific Maven coordinates depend on the dependency configuration of the project, and you can refer to the official eXtremeDB documentation to obtain the latest Maven coordinates.