使用Result Transformer计算Hibernate 4.1 Count Projection Type Mismatch(Long/Integer)

Question

我有一个实体bean FooEntity和DAO方法来获取由该实体上的属性分组的行计数,封装在视图模型bean中FooCount.

public List<FooCount> groupByFoo() {
    return sessionFactory.getCurrentSession()
        .createCriteria(FooEntity.class)
        .setProjection(Projections.projectionList()
            .add(Projections.groupProperty("foo"), "foo")
            .add(Projections.count("foo"), "count")
        ).setResultTransformer(Transformers.aliasToBean(FooCount.class))  
        .list();
}

public class FooCount {
    private String foo;
    private Integer count; // <-- this is the problem
    // getters/setters...
}

运行它会产生异常,因为Projections.count()产生一个Long而不是一个Integer.

org.hibernate.PropertyAccessException: IllegalArgumentException occurred while calling setter of FooCount.count
    at org.hibernate.property.BasicPropertyAccessor$BasicSetter.set(BasicPropertyAccessor.java:119)
--snip--
    Caused by: java.lang.IllegalArgumentException: argument type mismatch

它可以工作,如果我count改为a Long但我宁愿不更改视图模型类,因为它使用的是其他各种地方.

我可以Projections.count()以Integer某种方式返回或使结果转换器转换Long为Integer？

Answer 1

您可以使用 SQL 投影将其转换为 Integer：

.setProjection( Projections.sqlProjection(
    "Cast(Count(foo) as Integer) count",
    new String[]{"count"},
    new Type[]{StandardBasicTypes.INTEGER}
)