如何为多对多关联编写 HQL 查询?
我有 3 个表,Role[roleId, roleName]
、Token[tokenID, tokenName]
& ROLETOKENASSOCIATION[roleId,tokenID]
。第三个是由 hibernate 自动创建的。现在,如果我简单地编写一个查询来从角色类中获取所有对象,它会给出所有角色对象以及关联的 tokenID 和 tokenID。令牌名称。
我只是希望这种关联是单向的。即:角色--->令牌 所以 Role 类中的注释看起来像,
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private int roleId;
private String roleName;
@ManyToMany
@JoinTable(name="ROLE_TOKEN_ASSOCIATION",
joinColumns={@JoinColumn(name="roleId")},
inverseJoinColumns={@JoinColumn(name="tokenID")})
private List<Token> tkns;
//Getters & Setters
现在我想要特定 roleId 的 tokenNames。 首先我做了一个这样的查询 SELECT tkns.tokenName FROM Role WHERE Role.roleId=:roleId
但是,我最终遇到了一些取消引用错误。
然后我将查询更改为 SELECT tkns FROM Role r WHERE r.roleId=:roleId 现在我已经得到了我想要的。但它也带有 roleId。
我该如何获取 tokenName 本身? 其实我的问题已经解决了,但我想知道该怎么做。
如果有人解释查询构造,这对我会有帮助。
任何建议!
I have 3 tables, Role[roleId, roleName]
, Token[tokenID, tokenName]
& ROLETOKENASSOCIATION[roleId, tokenID]
. The 3rd one was created automatically by hibernate. Now if i simply write a Query to get all the objects from Role class means, it gives the all role objects along with the associated tokenID & tokenName.
I just wanted the association as unidirectional. i.e: Roles--->Tokens
So the annotation in the Role class looks like,
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private int roleId;
private String roleName;
@ManyToMany
@JoinTable(name="ROLE_TOKEN_ASSOCIATION",
joinColumns={@JoinColumn(name="roleId")},
inverseJoinColumns={@JoinColumn(name="tokenID")})
private List<Token> tkns;
//Getters & Setters
Now i want the tokenNames for the specific roleId.
First i made a query like this SELECT tkns.tokenName FROM Role WHERE Role.roleId=:roleId
But, i ended up with some dereference error.
Then i changed the query to SELECT tkns FROM Role r WHERE r.roleId=:roleId
Now i have got what i wanted. But it comes with roleId too.
How shall i get tokenName itself?
Actually my problem is solved, but i would like to know how to do it.
It ll be helpful to me, if anyone explains the Query Construction.
Any suggestions!!
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您是否尝试过
编辑:此查询几乎直接映射到相应的 SQL 查询,其中
Role r JOIN r.tkns t
是通过链接表进行 SQL 连接的简写语法<代码>角色 r JOIN ROLETOKENASSOCIATION rt ON r.roleId = rt.roleId JOIN Token ON rt.tokenId = t.tokenId。 Affe 的答案是同一查询的另一种语法。另请参阅:
Have you tried
EDIT: This query almost directly maps to the corresponding SQL query where
Role r JOIN r.tkns t
is a shorthand syntax for the SQL join via the link tableRole r JOIN ROLETOKENASSOCIATION rt ON r.roleId = rt.roleId JOIN Token ON rt.tokenId = t.tokenId
. Affe's answer is another syntax for the same query.See also:
您想要一个仅包含名称字段的标量列表吗?你应该能够像这样得到它
You want a scalar list of just the name field? You should be able to get that like this