在hql查询中选择多个new()对象 [英] select multiple new() object in hql query

问题描述

我对hql语言有疑问.我正在尝试通过WCF REST应用程序上的hql语法生成DTO.我对第二个查询有疑问.怎么了还有其他方法可以达到相同的结果吗?

I have a question about hql language. I'm trying to generate DTO's via hql syntax on my WCF REST application. I have a problem with the second query. What is wrong with it? Is there any other way to reach the same result?

这很好.

session.CreateQuery(@"select new EntityTypeDTO(t.ID, t.Title, assc.ID)
                            from crmEntityType t
                          left outer join t.Association as assc").List<EntityTypeDTO>();

这不起作用.

session.CreateQuery(@"select new EntityTypeDTO(t.ID, t.Title, assc.ID, new CustomFieldDTO(f.ID,f.EntityType,f.FieldType,f.Name,f.Value))
                            from crmEntityType t
                          join fetch t.Fields as f
                          left outer join t.Association as assc").List<EntityTypeDTO>();

推荐答案

好吧，new Xxx(field1, field2, ...)语法只是在查询中创建这些DTO的便捷方式.它不是一种完全成熟的编程语言，因此，它很可能不支持嵌套的new调用，如您的new EntityTypeDTO(..., new CustomFieldDTO(...)).

Well, the new Xxx(field1, field2, ...) syntax is just a convenience way for creating those DTOs in a query. It is not a fully fledged programming language and as such it most probably won't support nested new calls like your new EntityTypeDTO(..., new CustomFieldDTO(...)).

您可以做的是在Object[]中选择字段并自己调用构造函数，例如像这样:

What you could do instead is select the fields into a Object[] and call the constructors yourself, e.g. like this:

List<Object[]> result = query.getResultList();

for( Object[] line : result ) {
  //this is just an example, the order depends on the field order in the select clause
  //and you'd need some casts/conversion
  new EntityTypeDTO(line[0], line[1], line[2], new CustomFieldDTO(line[3], ...));
}

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