Java QueryDSL 3.6.0 Projection.bean（Person.class、Person.firstName、Person.count（））

我在项目中使用QueryDSL返回按姓氏分组的人员列表和具有该姓氏的人数。下面是Person.java

@Entity
class Person {
     private String firstName;
     private String lastName;
     private boolean isCitizen;
     private int age;
     private int groupByCount; //Property to return groupByCount - could use Group tuple for this, but doing a research trying to set it as an object field.

     //Constructors to support n! ways of object creation - where n is no of fields in the object
     public Person(String lastName, int groupByCount){
       this.lastName = lastName;
       this.groupByCount = groupByCount;
     }

     public Person(int age, int groupByCount){
       this.age = age;
       this.groupByCount = groupByCount;
     }

     public Person(boolean isCitizen, int groupByCount){
       this.isCitizen = isCitizen;
       this.groupByCount = groupByCount;
     }

     // keeps going to cover all possible constructors - i want to avoid this for maintainability reasons - want to be able to build objects dynamically with different parameters

     //Below is code for Getter and setters for above fields
}

下面是使用这些构造函数的QueryDSL查询

personRepo.getQueryDSL().createQuery(person).groupBy(person.lastName)
.list(Projections.constructor(Alarm.class, person.lastName, person.count());

personRepo.getQueryDSL().createQuery(person).groupBy(person.age)
.list(Projections.constructor(Alarm.class, person.age, person.count());

personRepo.getQueryDSL().createQuery(person).groupBy(person.isCitizen)
.list(Projections.constructor(Alarm.class, person.isCitizen, person.count());

如何避免写那些n！使用QueryDSL？的具有n个字段的类的构造函数？？在删除Person类中的构造函数后，我尝试了如下Projections.bean

personRepo.getQueryDSL().createQuery(person).groupBy(person.isCitizen)
.list(Projections.bean(Alarm.class, person.isCitizen, person.count());

它抱怨。count（）不是有效的表达式。值得注意的是，将count的值指定给person对象中的groupByCount字段。如何使用Projections.bean方法将person对象的groupByCount设置为person.count（）值

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提前谢谢。非常感谢您的帮助。

我相信这正是您需要的。让POJO中的setter名称镜像查询中的列名-看起来您已经准备好了它。

我将.as方法链接到.count到groupByCount属性之上，如下所示。这样我就可以避免写n！构造器

personRepo.getQueryDSL().createQuery(person).groupBy(person.isCitizen)
.list(Projections.bean(Alarm.class, person.isCitizen,
person.count().as(person.groupByCount));