休眠映射到一个表中的一对多

Question

We have the following (poorly designed?) table:

inputs:
keyword_id serial not null,
group_name string not null,
banned_term string not null

Keyword ID is the primary key. there are many banned terms per group_name. The data looks like this:

keyword_id | group_name | banned_term
1 | incentivization | free money
2 | inaccuracy | we're number one
3 | incentivization | win a free ipod!

There's no join table, and group_name isn't its own entity. I'd like a domain object something like this:

class BannedTermGroup {
  Integer id;
  String group_name;
  Set<String> banned_terms;

  // ... various getters and setters
}

The only examples on this one-to-many relationship between the group name and banned terms all involve some sort of join column or join table, while group_name would always be part of some other entity. Here neither is the case. Can this be mapped using Hibernate?

Answer 1

As quoted in my previous comment, you can get the ID of the group from nowhere.

Just to put aside this problem, you may look into Hibernate's reference, search for collections of basic types. It is what you need.

However, you still need to have a table for the "group".

assume it is as simple as a one column table:

KEYWORD_GROUP
--------------------
GROUP_NAME   STRING

Your original keyword table:

KEYWORD
--------------------
GROUP_NAME   STRING
KEYWORD      STRING

I believe this is what you need:

@Entity
@Table("KEYWORD_GROUP")
public class KeywordGroup {
   [.....]

   @ElementCollection
   @CollectionTable(name="KEYWORD", joinColumns=@JoinColumn(name="GROUP_NAME"))
   @Column(name="KEYWORD")
   private List<String> keywords;
}

For the keyword_group table, you probably don't need to create a new table if you are just using this model for read. Create a view from your original keyword table should be good enough.