JPAContainer addNestedContainerProperty "Invalid property"

I have two entities and would show data from this in one table

In SQL I make this with the following SQL Statement:

Select werk., firma. From werk Inner Join firma On werk.firmaID = firma.ID

public class TestJoinTables extends Window {
private JPAContainer werkContainer;
public TestJoinTables() {
werkContainer = JPAContainerFactory.make(Werk.class, Schulung.PERSISTENCE_UNIT);


    Table filterTable = new Table();
    // FilterTable filterTable = new FilterTable();


I think it should work with addNestedContainerProperty, but i get an error “Invalid property name”

How could I solve this problem? Should I use another Container?

In the attachment you could find my two entities, they have a @ManyToOne relation (672 Bytes) (1.08 KB)

I have a solution

class firma:
@OneToMany(mappedBy = “firmaID”, targetEntity = Werk.class, cascade = CascadeType.ALL)
private Set werks;

class werk:
@ManyToOne(targetEntity = Firma.class, cascade = CascadeType.ALL)
private Firma firmaID;