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Developing Hibernate Applications
4.7. 关于动态注入

4.7. 关于动态注入

特定的表达式类型仅在 select 子句中有效。Hibernate 将此"动态实例化"称为"动态实例化"。Jakarta Persistence 查询语言支持部分功能，并将其称为"结构表达式"。

示例：动态注入示例 - 结构

select new Family( mother, mate, offspr )
from DomesticCat as mother
    join mother.mate as mate
    left join mother.kittens as offspr

select new Family( mother, mate, offspr )
from DomesticCat as mother
    join mother.mate as mate
    left join mother.kittens as offspr

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因此，我们不在这里处理 Object[]，而是在 type-fe Java 对象中嵌套这些值，该对象将作为查询的结果返回。类引用必须完全限定，并且必须具有匹配的构造器。

此处的类不需要映射。如果确实代表某一实体，则生成的实例将返回为 NEW 状态（非 managed!）。

这也是 Jakarta Persistence 查询语言支持的部分。HQL 支持其他"动态实例化"功能。首先，查询可以指定返回列表，而不是用于 scalar 结果的 Object[]：

示例：动态注入示例 - 列表

select new list(mother, offspr, mate.name)
from DomesticCat as mother
    inner join mother.mate as mate
    left outer join mother.kittens as offspr

select new list(mother, offspr, mate.name)
from DomesticCat as mother
    inner join mother.mate as mate
    left outer join mother.kittens as offspr

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这个查询的结果将是 List<List>，而不是 List<Object[]>。

HQL 还支持将井号结果换算成一个映射。

示例：动态注入示例 - 映射

select new map( mother as mother, offspr as offspr, mate as mate )
from DomesticCat as mother
    inner join mother.mate as mate
    left outer join mother.kittens as offspr

select new map( max(c.bodyWeight) as max, min(c.bodyWeight) as min, count(*) as n )
from Cat cxt

select new map( mother as mother, offspr as offspr, mate as mate )
from DomesticCat as mother
    inner join mother.mate as mate
    left outer join mother.kittens as offspr

select new map( max(c.bodyWeight) as max, min(c.bodyWeight) as min, count(*) as n )
from Cat cxt

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这个查询的结果将是 List<Map<String,Object>>，而不是 List<Object[]>。映射的键由提供给所选表达式的别名定义。

4.7. 关于动态注入

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