使用JPA标准在没有关系的情况下联接表

问题描述

我有两个没有建模关系的表:

I have two tables with no modeled relation:

具有列的表comm:

name
date
code

具有列的表persondesc:

code
description

两个表之间的关系是多对一的(许多 comm 对一个 persondesc ):

Relationship between the two tables is many to one (many comm to one persondesc):

com.code = persondesc.code

这两个表都映射有注释，但是我没有声明任何关系.

These two tables are mapped with annotations but I have no relation declared.

我要尝试的是选择persondesc.description排序的comm表.

What I'm trying to is to select comm table ordered by persondesc.description.

我该如何执行JPA和Hibernate?

How can I do this JPA and Hibernate?

推荐答案

因此，如果您的类没有关系"，则可以执行类似的查询

So if your classes have no "relation" then you do a query like

SELECT a FROM A a, B b WHERE a.someField = b.otherField ORDER BY b.anotherField

使用JPA标准可以实现哪些目标，例如

Which can be achieved using JPA Criteria, something like

CriteriaBuilder cb = emf.getCriteriaBuilder();
CriteriaQuery<A> crit = cb.createQuery(A.class);
Root<A> aRoot = crit.from(A.class);
Root<B> bRoot = crit.from(B.class);
aRoot.alias("a");
bRoot.alias("b");
crit.select(aRoot);
Predicate fieldEquals = cb.equal(aRoot.get(A_.someField), bRoot.get(B_.otherField);
crit.where(fieldEquals);
crit.orderBy(cb.asc(bRoot.get(B_.anotherField)));

...或者只是重新设计您的类，对您的开发人员有所帮助.

... Or just redesign your classes and do your developers a favour.

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