querydsl-collections 和 groupBy

Question

我正在尝试使用 querydsl-collections，但未能编写简单的 groupBy 表达式。这是我的尝试：

 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;
         }

     }

 }

但是当我尝试运行它时。我明白了：

 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)

这是一个错误吗？

Answer 1

Querydsl Collections https://github.com/querydsl/querydsl/issues/932987654321@ 中尚不支持聚合投影