[英]Hibernate criteria + calculation in Projection List
id 描述 率 金額
1張 發票A 3.0 10.0
2張 發票B 4.0 20.0
3 發票C 5.0 30.0
DetachedCriteria criteria= DetachedCriteria.forClass(Invoice.class)
ProjectionList projList = new ProjectionList();
projList.add(...);
criteria.setProjection(projList);
List list = myDAO.findByCriteria(criteria);
//260
使用投影列表,是否可以計算(金額*費率)並返回所有記錄的總和?
更新1:
double dblAmount = 0.0;
for(Invoice invoice : list){
dblAmount = dblAmount + (invoice.getRate() * invoice.getAmount());
}
使用Hibernate 4,我聽說沒有指定連接,使用這種方式(invoice.getSomething())是否會對性能產生影響?
您可以創建一個@Formula
派生的屬性,然后在該屬性上創建一個投影:
派生屬性:
@Entity
@Table(name="INVOICE")
public class Invoice {
private double rate;
private double amount;
@Formula("rate * amount")
private double computed;
// ...
}
投影:
Projections.sum("computed")
double sum=0;
ProjectionList projList = new ProjectionList();
projList.add(Projections.property("rate"));
projList.add(Projections.property("amount"));
criteria.setProjection(projList);
List list=criteria.list();
for (Iterator it = list.iterator(); it.hasNext();) {
double d=1;
Object[] row = (Object[]) it.next();
for (int i = 0; i < row.length; i++) {
d=d*Double.parseDouble(row[i].toString());
}
sum=sum+d;
}
return sum;
嘗試這個。
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