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DiscountCalculator.java
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DiscountCalculator.java
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package com.company.sample.core;
import com.haulmont.cuba.core.Persistence;
import com.haulmont.cuba.core.Query;
import org.springframework.stereotype.Component;
import javax.inject.Inject;
import java.math.BigDecimal;
import java.util.UUID;
/**
* Managed bean of the middle tier providing calculation of customer discounts.
*/
@Component("sample_DiscountCalculator")
public class DiscountCalculator {
@Inject
private Persistence persistence;
/**
* Calculates discount for a given customer. Expects that an active transaction exists at the moment.
* @param customerId customer id
* @return discount value
*/
public BigDecimal calculateDiscount(UUID customerId) {
// Calculate the total amount on the database level - the fastest possible way
Query query = persistence.getEntityManager().createQuery(
"select sum(e.amount) from sample$Order e where e.customer.id = :custId");
query.setParameter("custId", customerId);
BigDecimal sum = (BigDecimal) query.getSingleResult();
if (sum == null)
sum = BigDecimal.ZERO;
// Decide about discount
BigDecimal discount = BigDecimal.ZERO;
if (sum.intValue() > 300)
discount = new BigDecimal("30");
else if (sum.intValue() > 200)
discount = new BigDecimal("20");
else if (sum.intValue() > 100)
discount = new BigDecimal("10");
// Add some randomness to always get a new value for the demonstration purpose
discount = discount.multiply(new BigDecimal(Math.random()));
return discount;
}
}