playframework 2.0 - Save to an ArrayList of a model object -

i using play framework 2.0.4 , in model class 1 of variables array list<long> datatype, declared here:

public list<long> associatebooks = new arraylist<long>();  

i have view template invokes controller method 2 long values represent id's of 2 different objects of same model type.

get     /addassociate/:oid/:id              controllers.application.addassociate(oid: long, id: long) 

the controller method invoked:

public static result addassociate(long oid, long id) {      book.addassociate(oid, id);     return redirect(routes.application.index()); } 

i know controller method performing action because redirected index page , know receives values because url changes expected.

the problem lies in book model method addassociate shown below.

public static void addassociate(long oid, long match) {      list<book> allbooks = new arraylist<book>();     allbooks = find.all();      for(book book: allbooks) {          if(book.id == oid) {             book.associatebooks.add(match);             book.save();         }     } } 

in method want go through book objects , if id matches value of variable oid passed view controller want add value of match (the other arguement) associatebooks list (of type long) belongs each journey object. try , save changes object being considered during iteration. problem list associatebooks still seems empty when print out on other view templates.

update: if remove condition still doesn't add list.

if want save list of associated books, maybe follow this:

note: suggest create additional table named book_associated.

+--------+-------------------+ |book_id |associated_book_id | +--------+-------------------+ |1       |2                  | |1       |3                  | +--------+-------------------+ 

it means book id 1 associated book id 2 , 3

but, has disadvantages if book 1 associated book 2 cannot determine if book 2 associated book 1 because didn't declared on table.

so on model should below:

@entity @table(name = "book") public class book extends model {     @id     public long id;      // other fields     ...      @manytomany     @jointable(name="book_associated",         joincolumns=         @joincolumn(name="book_id", referencedcolumnname="id"),         inversejoincolumns=         @joincolumn(name="associated_book_id", referencedcolumnname="id")     )     public list<book> associatebooks = new arraylist<>();      // other methods , finder     ...  } 

here can save list of associated book of book. reference many-to-many relation on java :

1. http://en.wikibooks.org/wiki/java_persistence/manytomany
2. http://www.objectdb.com/api/java/jpa/manytomany