[英]Hibernate criteria + calculation in Projection List
id description rate amount id 描述 率 金额
1 Invoice A 3.0 10.0 1张 发票A 3.0 10.0
2 Invoice B 4.0 20.0 2张 发票B 4.0 20.0
3 Invoice C 5.0 30.0 3 发票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
Using projection list, is it possible to calculate (amount * rate) and return the sum for all records? 使用投影列表,是否可以计算(金额*费率)并返回所有记录的总和?
Update 1: 更新1:
double dblAmount = 0.0;
for(Invoice invoice : list){
dblAmount = dblAmount + (invoice.getRate() * invoice.getAmount());
}
Using Hibernate 4, I heard that without specifying joins, using this way (invoice.getSomething()) has performance impact? 使用Hibernate 4,我听说没有指定连接,使用这种方式(invoice.getSomething())是否会对性能产生影响?
You can create a @Formula
derived property and then create a projection on that: 您可以创建一个
@Formula
派生的属性,然后在该属性上创建一个投影:
Derived property: 派生属性:
@Entity
@Table(name="INVOICE")
public class Invoice {
private double rate;
private double amount;
@Formula("rate * amount")
private double computed;
// ...
}
Projection: 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;
try this. 尝试这个。
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