Loading data from existing connector table in JPA -

i'm beginner in jpa mapping. have simple entity (essentially 2d matrix) specifying value every product group/cost group combination.

@entity public class costdistribution {     @id     @generatedvalue(strategy=generationtype.auto)     private long id;      @notnull     @onetoone     private productgroup productgroup;      @notnull     @onetoone     private costgroup costgroup;      private long value; } 

now i'd read-only access relevant column of matrix when productgroup loaded (i.e. load costdistribution records product_group_id equals id of current product group). cannot figure out how this. tried:

@elementcollection @collectiontable(name="cost_distribution", joincolumns=@joincolumn(name="product_group_id")) 

but exception: same physical table name [cost_distribution] references several logical table names: [costdistribution], [cost_distribution]

what misunderstanding here?

@entity public class productgroup {     @id     @generatedvalue(strategy=generationtype.auto)     private long id;      @column(length=50)     @notnull     @size(max=50)     private string name;      @???     private list<costdistribution> costdistribution; } 

correct answer load relevant data matrix:

@onetomany(mappedby="productgroup", fetch=fetchtype.eager) private list<costdistribution> costdistribution; 

this joins in correct column connector table. example, when loading product group id=1:

select productgro0_.id id1_6_0_, productgro0_.name name2_6_0_, ..., costdistri1_.value value2_2_2_,  product_group productgro0_  left outer join cost_distribution costdistri1_ on productgro0_.id=costdistri1_.product_group_id  left outer join cost_group costgroup2_ on costdistri1_.cost_group_id=costgroup2_.id productgro0_.id=1