题
有:
class Container {
@Id
@Column(name="id")
protected long id;
@OneToMany
@JoinColumn(name="container_id", nullable=false)
protected Collection<Content> contents = new ArrayList<Content>();
}
和
class Content {
@Id
@Column(name="id")
protected long id;
@Column(name="link_id")
protected long linkId;
}
哪些JPQL查询将获得具有某些ID和某些链接的容器中的内容实体?
解决方案
如果不进行双向协会,您可以做:
SELECT c
FROM Content c, Container container
WHERE c MEMBER OF container.contents AND c.linkId = :linkId AND container.id = :containerId
但是,使协会双向更容易:
SELECT c from Content c
WHERE c.container.id = :containerId AND c.linkId = :linkId
并且生成的SQL看起来更好(并且更有效)。
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