sql - 在 JPQL 请求中使用新语句

Question

我用 new在 JPQL 查询中，如下所示

select 
  ob.property1,
  NEW package1.CustomObject(item, dimension, material, product)
from mainTable ob
LEFT JOIN ....

应用程序提示 ob.property1 后昏迷说这是一个意外的 token 。似乎您不能在 new 中使用多列在 select 子句中。你能帮助我吗

Answer 1

根据 this您有以下选择:

将值包装在类型安全的 Java 对象中，该对象将作为查询结果返回。

select new package1.CustomObject(item, dimension, material, product)
from MainTable ...

The projection class must be fully qualified in the entity query, and it must define a matching constructor. The class here need not be mapped. It can be a DTO class. If it does represent an entity, the resulting instances are returned in the NEW state (not managed!).

HQL 支持额外的“动态实例化”功能。

查询可以指定返回 List而不是 Object[]对于标量结果。

select new list(item, dimension, material, product)
from MainTable ...

The results from this query will be a List<List> as opposed to a List<Object[]>.

将标量包装成 Map

select new map(
  item as iName,
  dimension as iDimension,
  material as iMaterial,
  product as iProduct)
from MainTable ...

The results from this query will be a List<Map<String, Object>> as opposed to a List<Object[]>. The keys of the map are defined by the aliases given to the select expressions. If the user doesn’t assign aliases, the key will be the index of each particular result set column (e.g. 0, 1, 2, etc).