Spring JPA @Query 如何连接子表和父表？答案

【问题标题】：Spring JPA @Query How to join child and parent tables?Spring JPA @Query 如何连接子表和父表？
【发布时间】：2020-08-30 01:31:25
【问题描述】：

Class Entry {
    int id;
    String name;
}
Class NewEquipment extends Entry{
    int id;
    String name;
    String type;
}
Class Inventory extends Entry{
    int id;
    String name;
    String location;
}

db中有三个类和相关的表，现在我需要查询如下：

 @Query(value = "SELECT ne FROM Entry e INNER JOIN NewEquipment ne WHERE e.id = ne.id")

它抛出异常如下，我不知道如何使用 JPA 加入子类和父类，我将不胜感激。谢谢！

Caused by: java.lang.IllegalStateException: No data type for node: org.hibernate.hql.internal.ast.tree.IdentNode 
 \-[IDENT] IdentNode: 'ne' {originalText=ne}
    at org.hibernate.hql.internal.ast.tree.SelectClause.initializeExplicitSelectClause(SelectClause.java:174)
    at org.hibernate.hql.internal.ast.HqlSqlWalker.useSelectClause(HqlSqlWalker.java:937)
    at org.hibernate.hql.internal.ast.HqlSqlWalker.processQuery(HqlSqlWalker.java:705)
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.query(HqlSqlBaseWalker.java:665)
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.selectStatement(HqlSqlBaseWalker.java:301)
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.statement(HqlSqlBaseWalker.java:249)
    at org.hibernate.hql.internal.ast.QueryTranslatorImpl.analyze(QueryTranslatorImpl.java:278)
    at org.hibernate.hql.internal.ast.QueryTranslatorImpl.doCompile(QueryTranslatorImpl.java:206)
    at org.hibernate.hql.internal.ast.QueryTranslatorImpl.compile(QueryTranslatorImpl.java:158)
    at org.hibernate.engine.query.spi.HQLQueryPlan.<init>(HQLQueryPlan.java:131)
    at org.hibernate.engine.query.spi.HQLQueryPlan.<init>(HQLQueryPlan.java:93)
    at org.hibernate.engine.query.spi.QueryPlanCache.getHQLQueryPlan(QueryPlanCache.java:167)
    at org.hibernate.internal.AbstractSessionImpl.getHQLQueryPlan(AbstractSessionImpl.java:301)
    at org.hibernate.internal.AbstractSessionImpl.createQuery(AbstractSessionImpl.java:236)
    at org.hibernate.internal.SessionImpl.createQuery(SessionImpl.java:1836)
    at org.hibernate.jpa.spi.AbstractEntityManagerImpl.createQuery(AbstractEntityManagerImpl.java:328)
    at sun.reflect.GeneratedMethodAccessor71.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at

【问题讨论】：

您是否使用实体之间的任何关系？如果没有定义Join On 子句。请向我们提供正确的信息，以便我们重现您的问题。

标签： mysql spring hibernate jpa

【解决方案1】：

在这个任务中使用@Query 有什么意义？您应该简单地定义适当的数据模型，spring/hibernate 将为您做连接表；这是一个简单的例子 - https://tenmilesquare.com/spring-boot-jpa-relationship-quick-guide/

【讨论】：