Primary key issue with adf Entry Form.

Question

Hi All,
i'm using jdev version 11.1.1.5.0
use case: i have create simple entry form based on Eo and Vo using database table like student(enrollment no,name address)
where enrollment no is primary key.
so when i have create a record i have set enrollment no in entity impl class of this eo create method using some logic based on my need like(20130001)
for that i have read highest no from database field and assign to enrollment no field when user create record.
so when user create record second time then enrollment no is 20130002. and other detail like name and address user fill and commit record. and it is fine.
but problem is that when two user access same form at a time and create record so both have get same primary key like 20130003 because in current time in database maximum value is 20130002.
so which user  commit record first it record will save on database and second user get error message because of primary key violation.
so my question is that where we generate primary key value for record so when multiple user access form have get different primary key value. and in my use case i can't use sequence and any autoincrement no
because i have patter for primary key.
Thanks in Advance
Manish

Answer 1

Hi,
Dimitar and Frank
thank for reply.
How can i apply non-concurrent DB lock can you please explain.(because lock method on entity impl not work when user create new row as per documentation)
http://docs.oracle.com/cd/B14099_19/web.1012/b14022/oracle/jbo/server/EntityImpl.html#lock__
i have write following line of code in entity impl class to set primary key value(reqid)-
    @Override
    protected void prepareForDML(int i, TransactionEvent transactionEvent) {
         super.prepareForDML(i, transactionEvent);
        this.setReqid(genReqid());
    public String genReqid() {
        String reqby = this.getReqby();
        String qry =
            "SELECT nvl(MAX(TO_NUMBER(SUBSTR(REQID,7))),0)+1  FROM STM_REQHDR WHERE REQBY=? AND REQTYPE<>'M' and substr(reqid,1,2)<>'MT' AND SUBSTR(REQID,1,3)<>'PAY'";
        PreparedStatement ps = null;
        String no = "";
        try {
            ps = getDBTransaction().createPreparedStatement(qry, 0);
            ps.setString(1, reqby);
            ResultSet rs = ps.executeQuery();
            if (rs.next()) {
                no = rs.getString(1);
            ps.close();
        } catch (Exception e) {
            System.out.println("Exception in Gen req id ==>" + e);
        String reqno = reqby + String.format("%6s", no).replace(' ', '0');
        return reqno;
but when i run form in debug mode and two user commit concurrent manner only one time code block is executed who first commit. and second user got error message.
thanks
Manish