EJB transaction logic with locking

Hi,

I have 2 stateless container managed transaction beans called OrderSLB and ContractSLB and one CMP bean OrderEB wrapping around an order table.

The orderslb has a method called updateOrder() defined with a Required attribute. This method does the update on the order row be looking up the OrderEB bean by findByPrimaryKey() (...besides some other operation ...)

The second bean contract bean has a method called executeContract() been defined with Required attribute. This method does 3 things
1) Check for business validity.
2)updates a status field in the order table so looks up the orderEB to do the job
3) Inserts a record in the Contract table.

The ordereb has ben set with a repeatable read serializable transcation isolation

When 2 user do a simultaneous where one does an updateOrder() and one and executeContract() I want only one user to succeed and i should be able to give an error message to the other user.  

Now i get a number of outputs when i try to do the operations simultaneously. One of them is : the updateorders() happenes first, then the update of status on the executeContract(). (note this happens between the validity check and the change of status...) Businesswise this is a bad situation. How do i prevent this ? How do i implement locking so that i know when i start the trasaction for exceuteContract() the order will not be updated

Im using Weblogic 5.1 and Oracle 8.0.6

Saba