Using Composite keys in Entity Beans

Question

Hi, I am trying to develop a test application with two entity beans, (1) OrderBean (key is a string called order_no) and (2) LineBean (key is order_no and an integer line_no) using CMP 2.0. Relationship between OrderBean to LineBean is 1 to many. I created a primary key class for LineBean called, LinePK with both order_no and line_no as the public members. My home interface for LineBean has the following three finder methods:
public java.lang.Object findByPrimaryKey(LinePK lkey);
public Collection findByOrder(String order_no);
public Collection findByProduct(String product_id);
I could provide sql for the OrderBean which has only one field(order_no) as primary key, but I don't know how to code appropriate SQL for the finder methods of LineBean involving a user defined primary key class (in my case LinePK with order_no and line_no). I am trying to deploy this application in J2EE RI server, but getting deployment errors saying invalid return types for the finder methods. In the deploytool I provided the primary key class for LineBean as java.lang.Object with no primary key field name. Any help in this matter with sample sql code is greatly appreciated. Thanks !!!

Answer 1

Some things to consider:
- Your findByPrimaryKey in the Remote interface needs to have the remote interface as return type
- The implementation of the finder needs to have your primary key class as return type
- If you're using CMP 2.0, you need to specify the search criteria as EJB QL
Using CMP 2.0, you don't code findByPrimaryKey at all, all you need is the EJB QL for findByOrder/findByProduct in the deployment descriptor. The EJB QL for findByOrder would look like:
select Object o from Line where o.order_no = ?1If you use BMP, you would code the findByPrimaryKey implementation like this:
public LinePK ejbFindByPrimaryKey(LinePK pk) throws FinderException {
  String sql = "select order_no from line_table where line_no=? and order_no=?";
  InitialContext ic = new InitialContext();
  Object obj = ic.lookup("datasourcename");
  DataSource ds = (DataSource)PortableRemoteObject.narrow(obj, DataSource.class);
  Connection conn = ds.getConnection();
  try {
    PreparedStatement stmt = conn.prepareStatement(sql);
    try {
      stmt.setInteger(1, pk.line_no);
      stmt.setInteger(2, pk.order_no);
      ResultSet rs = stmt.executeQuery();
      if (!rs.next())
        throw new ObjectNotFoundException("not found: " + order_no + "." + line_no);
      return pk;
    finally {
      stmt.close();
  finally {
    conn.close();