java 从 SQLProjection 中引用外部条件查询别名
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Referencing outer criteria query aliases from within an SQLProjection
提问by EkcenierK
I am aware that you can use {alias}to refer to the root entity within an SQLProjection:
我知道您可以使用{alias}来引用 SQLProjection 中的根实体：
Projections.sqlProjection("MIN({alias}.field) as value", new String[]{"value"}, new Type[]{new LongType()}))
What I am trying to do is to reference an alias for a non-rootentity:
我想要做的是引用非根实体的别名：
Projections.sqlProjection("MIN(i.powerRestarts) as value", new String[]{"value"}, new Type[]{new LongType()}))
where iis an alias from the outer criteria query. The code above throws an SQL exception saying that i.powerRestartscannot be found.
wherei是来自外部条件查询的别名。上面的代码抛出一个 SQL 异常，说i.powerRestarts找不到。
Is it possible to refer to a non-root alias from an SQLProjection?
是否可以从 SQLProjection 中引用非根别名？
回答by EkcenierK
Having done some googling, it appears that this this is not possible - Hibernate only allows inclusion of the root entity alias using {alias}in the SQL string of the SQLProjection. I did however find this issue regarding the limitationon the Hibernate JIRA pages.
做了一些谷歌搜索后，这似乎是不可能的 - Hibernate 只允许{alias}在SQLProjection. 然而，我确实发现了这个关于Hibernate JIRA 页面限制的问题。
Someone has kindly submitted a patch that allows the use of non-root aliases in the SQLProjectionstring, through a new RestrictionsExtclass. Using my example from the question:
有人好心地提交了一个补丁，允许SQLProjection通过一个新RestrictionsExt类在字符串中使用非根别名。使用我的问题示例：
Projections.sqlProjection("MIN(i.powerRestarts) as value", new String[]{"value"}, new Type[]{new LongType()}))
The alias ican now be referenced as:
i现在可以将别名引用为：
RestrictionsExt.sqlProjection("MIN({i}.powerRestarts) as value", "value", new LongType())
I had to modify the static RestrictionsExt.sqlProjectionmethod to allow specification of the type for the column alias ("value") (here defined as LongType), as the patch didn't allow this and defaulted to StringType.
我不得不修改静态RestrictionsExt.sqlProjection方法以允许指定列别名 ( "value")（此处定义为LongType）的类型，因为补丁不允许这样做并且默认为StringType.
The SQLAliasedProjection class in the patch also requires access to the following private methods in org.hibernate.loader.criteria.CriteriaQueryTranslator: getOuterQueryTranslatorand getAliasedCriteria. To get this to work without modifying the Hibernate source, I used reflection:
补丁中的 SQLAliasedProjection 类还需要访问org.hibernate.loader.criteria.CriteriaQueryTranslator:getOuterQueryTranslator和 中的以下私有方法getAliasedCriteria。为了在不修改 Hibernate 源的情况下使其工作，我使用了反射：
cri = ((org.hibernate.loader.criteria.CriteriaQueryTranslator) criteriaQuery).getAliasedCriteria(alias);
was changed to:
改为：
Method m = ((org.hibernate.loader.criteria.CriteriaQueryTranslator) criteriaQuery).getClass().getDeclaredMethod("getAliasedCriteria", String.class);
m.setAccessible(true);
cri = (Criteria) m.invoke(((org.hibernate.loader.criteria.CriteriaQueryTranslator) criteriaQuery), alias);
Hopefully this will help anyone else facing the same problem.
希望这能帮助其他面临同样问题的人。
