是否有可能在Google App Engine上使用Java计算属性？ [英] Is it possible to have a computed property on Google App Engine using Java?

问题描述

我有一个应用程序引擎应用程序，我想运行一个查询，根据涉及两个属性的表达式对结果进行排序。到目前为止，我认为最好的方法是创建一个计算/计算的属性，存储该表达式的结果。虽然我看到Python中的GAE提供了一个ComputedProperty，这看起来正是我正在寻找的，但我无法在Java中找到相应的东西。

如果有帮助的话，我现在还在使用Objectify。

有什么想法？ 使用@OnSave方法计算您的值：

  @Entity 
 public class YourEntity {
 @Id长ID; 
 
 String foo; 
字符串栏; 
 
 @Index字符串计算; 
 
 @OnSave void computeComputed（）{
 computed = //从foo和bar合成
} 
} 
  

这是NDB的ComputedProperty实际所做的。 Java并没有真正的语法匹配方式，我不确定NDB的方法更优雅。只需放弃计算的setter方法。

I have an app engine application and I want to run a query that sorts the result based on a expression involving two properties. Best way I thought of doing it so far is to create a computed/calculated property that stores the result of that expression. Although I saw that GAE in Python offers a ComputedProperty, which seems to be exactly what I'm looking for, I couldn't find an equivalent in Java.

I'm currently using Objectify too, if that helps.

Any ideas?

解决方案

Compute your value in an @OnSave method:

@Entity
public class YourEntity {
    @Id Long id;

    String foo;
    String bar;

    @Index String computed;

    @OnSave void computeComputed() {
        computed = // synthesize from foo and bar
    }
}

This is what NDB's ComputedProperty actually does. Java doesn't really have a way of matching that syntax, and I'm not sure NDB's approach is any more elegant. Just leave off the setter method for computed.

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