Creating a two dimentional array in the Play! Framework - jpa

Question

I'm trying to store a table of data in a two dimensional collection.
Whenever I:
#OneToMany
public List<List<Cell>> cells;
I get a JPA error:
JPA error
A JPA error occurred (Unable to build EntityManagerFactory): Use of #OneToMany or #ManyToMany targeting an unmapped class: models.Table.cells[java.util.List]
Cell is a class that I created, it's basically a String decorator. Any ideas? I just need a two dimensional matrix that i can store.
#Entity public class Table extends Model {
#OneToMany
public List<Row> rows;
public Table() {
this.rows = new ArrayList<Row>();
this.save();
}
}
#Entity public class Row extends Model {
#OneToMany
public List<Cell> cells;
public Row() {
this.cells = new ArrayList<Cell>();
this.save();
}
}
#Entity public class Cell extends Model {
public String content;
public Cell(String content) {
this.content = content;
this.save();
}
}

Answer 1

As far as I know, #OneToMany only works with List of Entities. You are doing a List of a List, which is not an entity, so it fails.
Try to change the model to:
Table > Row > Cell
All of them via #OneToMany, so you can have your 2-dimensional structure but with Entities.
EDIT:
I believe your model declaration is not correct. Try this one:
#Entity public class Table extends Model {
#OneToMany(mappedBy="table")
public List<Row> rows;
public Table() {
this.rows = new ArrayList<Row>();
}
public Table addRow(Row r) {
r.table = this;
r.save();
this.rows.add(r);
return this.save();
}
}
#Entity public class Row extends Model {
#OneToMany(mappedBy="row")
public List<Cell> cells;
#ManyToOne
public Table table;
public Row() {
this.cells = new ArrayList<Cell>();
}
public Row addCell(String content) {
Cell cell = new Cell(content);
cell.row = this;
cell.save();
this.cells.add(cell);
return this.save();
}
}
#Entity public class Cell extends Model {
#ManyToOne
public Row row;
public String content;
public Cell(String content) {
this.content = content;
}
}
To create:
Row row = new Row();
row.save();
row.addCell("Content");
Table table = new Table();
table.save();
table.addRow(row);