I have a one-to-many relationship modeled using join table:
我有一个使用连接表建模的一对多关系:
create table t1 (id int primary key, name varchar(10) /*...*/);
create table t2 (id int primary key, name varchar(10) /*...*/);
create table t1_t2 (t1_id int, t2_id int, primary key (t1, t2));
The tables are supposed to model the relationship of one t1 to many t2. What is the right way to model these tables using JPA?
这些表应该模拟一个t1到多个t2的关系。使用JPA对这些表建模的正确方法是什么?
1 个解决方案
#1
50
The typical table for one T1 to many T2 is to have a foreign key on T2 pointing toward T1. The T1_T2 table is usually not needed.
一个T1到多个T2的典型表是在T2上指向T1的外键。通常不需要T1_T2表。
The JPA structure would then be a One-To-Many, possibly two-way.
然后,JPA结构将是一对多,可能是双向的。
There could be some arrangements, to make the structure you describe work. You could change T1_T2:
可能会有一些安排,以使您描述的结构起作用。你可以改变T1_T2:
- add a unique constraint on T2 (so that only one T2 is allowed)
在T2上添加一个唯一约束(这样只允许一个T2)
Is that really what you want?
这真的是你想要的吗?
Edited: yes, it is what you want ;-)
编辑:是的,这是你想要的;-)
I doubt you may find many examples on the net. I have no proved solution, but I would try something along these lines:
我怀疑你可能在网上找到很多例子。我没有经过证明的解决方案,但我会尝试这些方法:
In Hibernate annotation reference documentation, see "2.2.5.3.2.3. Unidirectional with join table" to get the idea. It looks like:
在Hibernate注释参考文档中,请参阅“2.2.5.3.2.3。带有连接表的单向”以获得想法。看起来像:
@Entity
public class Trainer {
@OneToMany
@JoinTable(
name="TrainedMonkeys",
joinColumns = @JoinColumn( name="trainer_id"),
inverseJoinColumns = @JoinColumn( name="monkey_id")
)
public Set<Monkey> getTrainedMonkeys() {
...
}
#1
50
The typical table for one T1 to many T2 is to have a foreign key on T2 pointing toward T1. The T1_T2 table is usually not needed.
一个T1到多个T2的典型表是在T2上指向T1的外键。通常不需要T1_T2表。
The JPA structure would then be a One-To-Many, possibly two-way.
然后,JPA结构将是一对多,可能是双向的。
There could be some arrangements, to make the structure you describe work. You could change T1_T2:
可能会有一些安排,以使您描述的结构起作用。你可以改变T1_T2:
- add a unique constraint on T2 (so that only one T2 is allowed)
在T2上添加一个唯一约束(这样只允许一个T2)
Is that really what you want?
这真的是你想要的吗?
Edited: yes, it is what you want ;-)
编辑:是的,这是你想要的;-)
I doubt you may find many examples on the net. I have no proved solution, but I would try something along these lines:
我怀疑你可能在网上找到很多例子。我没有经过证明的解决方案,但我会尝试这些方法:
In Hibernate annotation reference documentation, see "2.2.5.3.2.3. Unidirectional with join table" to get the idea. It looks like:
在Hibernate注释参考文档中,请参阅“2.2.5.3.2.3。带有连接表的单向”以获得想法。看起来像:
@Entity
public class Trainer {
@OneToMany
@JoinTable(
name="TrainedMonkeys",
joinColumns = @JoinColumn( name="trainer_id"),
inverseJoinColumns = @JoinColumn( name="monkey_id")
)
public Set<Monkey> getTrainedMonkeys() {
...
}