querydsl-collections and groupBy

Question

我試圖玩querydsl集合，但未能寫出簡單的groupBy表達式。這裏是我的嘗試：

import static com.mysema.query.alias.Alias.$; 
import static com.mysema.query.alias.Alias.alias; 
import static com.mysema.query.collections.CollQueryFactory.from; 
import static java.util.Arrays.asList; 

import java.util.List; 

import com.mysema.query.Tuple; 

public class QuerydslCollectionsGroupByTest { 

    public static void main(String[] args) { 
     List<Foo> foos = asList(
       new Foo("a1", 1), 
       new Foo("a1", 2), 
       new Foo("a1", 3), 
       new Foo("a2", 4), 
       new Foo("a2", 5), 
       new Foo("a2", 6) 
       ); 

     Foo f = alias(Foo.class, "foo"); 
     List<Tuple> result = from($(f), foos) 
       .groupBy($(f.getA())) 
       .list($(f.getA()), $(f.getSum()).sum()); 

     System.out.println(result); 

    } 

    public static class Foo { 
     private String a; 
     private Integer sum; 

     public Foo() { 
     } 

     public Foo(String a, Integer sum) { 
      this.a = a; 
      this.sum = sum; 
     } 

     public String getA() { 
      return a; 
     } 

     public Integer getSum() { 
      return sum; 
     } 

     public void setSum(Integer sum) { 
      this.sum = sum; 
     } 

     public void setA(String a) { 
      this.a = a; 
     } 

    } 

} 

但是，當我嘗試運行它。我得到：

Exception in thread "main" com.mysema.codegen.CodegenException: Compilation of public class Q_838101820_201273267_01405199074_997653153 { 

    public static com.mysema.query.Tuple eval(com.sopovs.moradanen.zkoss.QuerydslCollectionsGroupByTest.Foo foo, com.mysema.query.types.QTuple a1) { 
return (com.mysema.query.Tuple)(a1.newInstance(foo.getA(), sum(foo.getSum()))); } 

} 

    failed. 
/Q_838101820_201273267_01405199074_997653153.java:4: error: cannot find symbol 
return (com.mysema.query.Tuple)(a1.newInstance(foo.getA(), sum(foo.getSum()))); } 
                  ^
    symbol: method sum(Integer) 
    location: class Q_838101820_201273267_01405199074_997653153 
1 error 

    at com.mysema.codegen.JDKEvaluatorFactory.compile(JDKEvaluatorFactory.java:74) 
    at com.mysema.codegen.AbstractEvaluatorFactory.createEvaluator(AbstractEvaluatorFactory.java:128) 
    at com.mysema.codegen.AbstractEvaluatorFactory.createEvaluator(AbstractEvaluatorFactory.java:94) 
    at com.mysema.query.collections.DefaultEvaluatorFactory.create(DefaultEvaluatorFactory.java:125) 
    at com.mysema.query.collections.DefaultQueryEngine.project(DefaultQueryEngine.java:234) 
    at com.mysema.query.collections.DefaultQueryEngine.evaluateSingleSource(DefaultQueryEngine.java:192) 
    at com.mysema.query.collections.DefaultQueryEngine.list(DefaultQueryEngine.java:91) 
    at com.mysema.query.collections.AbstractCollQuery.list(AbstractCollQuery.java:202) 
    at com.mysema.query.collections.AbstractCollQuery.list(AbstractCollQuery.java:195) 
    at com.sopovs.moradanen.zkoss.QuerydslCollectionsGroupByTest.main(QuerydslCollectionsGroupByTest.java:27) 

這是一個錯誤嗎？

Answer 1

Querydsl集合中尚未支持聚合投影https://github.com/querydsl/querydsl/issues/932