java - Map<String, Entity> with composite key in Entity -

i've got following 2 tables:

table a:   int      id   varchar  x primary key (id)  table b:   int      a_id   varchar  locale   varchar  z primary key (a_id, locale) 

it's simple onetomany relation. table b contains the id (a_id) of referenced row in table a plus locale. means: every entry in a can have 0..* entries in table b, each 1 distinct locale value.

i have following 2 classes, should represent tables:

@entity @table(name="a") class {   @id   @column(name="id")   int id;    @column(name="x")   string x;    @onetomany(mappedby="a") // ???   @mapkey... // ???   map<string, b> bmap; }  @entity @table(name="b") class b {   @manytoone   @joincolumn(name="a_id")   a;    @column(name="locale")   string locale;    @column(name="z")   string z; } 

now 2 things missing:

1. the annotations map<string, b> bmap. don't know if should use @mapkey or @mapkeycolumn , how map composite key. , if should/have use @onetomany?

2. the b class of course needs composite key. should use @embeddedid or @idclass?

could provide example code scenario?

thank you!

working solution @ bottom

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i think, i've managed put things together. @ least generated sql tables right, though still have figure out how cascaded saving done...

@entity @table(name="a") public class {    @id @generatedvalue(strategy=generationtype.auto)    long id;     @column(name="x")    string x;     @onetomany(mappedby="id.a", cascade=cascadetype.all, orphanremoval=true)    @mapkey(name="id.locale")    map<string, b> bmap = new hashmap<string, b>(); }  @entity @table(name="b") public class b {    @embeddedid    bpk id;     @column(name="z")    string z; }  @embeddable public class bpk implements serializable {    @manytoone    @joincolumn(name="a_id")    a;     @column(name="locale")    string locale;     // equals + hashcode } 

when calling arepository.findbyid(...) hibernates gives:

hibernate: select * a a.id=? 

which correct.

but if call aentity.getbmap() fetches whole map, if want use aentity.getbmap().put("en", somebobject) , don't want read data it. that's okay now.

now i've figure out how cascaded saving work. when doing aentity.getbmap().put("en", somebobject); arepository.save(eentity); get

org.hibernate.id.identifiergenerationexception: null id generated for:class b 

i think i'm missing setters @embeddedid or it's fields.

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finally solved:

cascaded saving somehow didn't work @embeddedid composite key. thought , figured out, instead use @elementcollection! :).

so here's did:

@entity @table(name="a") public class {    @id @generatedvalue(strategy=generationtype.auto)    long id;     @column(name="x")    string x;     @elementcollection    @collectiontable(name="b", joincolumns=@joincolumn(name="a_id"))    @mapkeycolumn(name="locale")    map<string, b> bmap = new hashmap<string, b>(); }  @embeddable public class b {    @column(name="z")    string z; } 

hibernate outputs:

a = arepository.findbyid(...)

• hibernate: select * id=?

a.getbmap().put("en", somebobject)

• hibernate: select * b a_id=?

arepository.save(a)

• hibernate: insert b (a_id, locale, z) values (?, ?, ?)