Is there a way to SELECT and UPDATE rows at the same time?

Question

I\'d like to update a set of rows based on a simple criteria and get the list of PKs that were changed. I thought I could just do something like this but am worried about po

Answer 1

I have faced the same issue; I have to update the credit amount, and have to get modified time, along with credit details from DB. It is basically

SYNCHRONOUSLY/ATOMICALLY perform (UPDATE then GET) in MYSQL

I have tried many options and found one that solved my issue.

1) OPTION_1 SELECT FOR UPDATE

This is maintaining the lock till update (SYNC from GET to UPDATE), but i need lock after update till the GET.

2) OPTION_2 Stored procedure

Stored procedure will not execute synchronously like redis lua, So there also we need sync code to perform that.

3) OPTION_3 Transaction

I have used JPA entityManager like below, thought that before commit no one can update, and before commit i will get the updated object along with modified time (from DB). But i didn't get the latest object. Only commit i got the latest.

    try {
        entityManager.getTransaction().begin();
        //entityManager.persist(object);
        int upsert = entityManager.createNativeQuery(
        "update com.bill.Credit c set c.balance = c.balance - ?1
          where c.accountId = ?2 and c.balance >= ?1").executeUpdate(); 
             //c.balance >= ? for limit check
        Credit newCredit = entityManager.find(Credit.class, "id");
        entityManager.refresh(newCredit); //SHOULD GET LATEST BUT NOT
        entityManager.getTransaction().commit();
    } finally {     
        entityManager.unwrap(Session.class).close();
    } 

4) OPTION_4 LOCK solved the issue, so before update i acquired the lock; then after GET i have released the lock.

private Object getLock(final EntityManager entityManager, final String Id){

    entityManager.getTransaction().begin();
    Object obj_acquire = entityManager.createNativeQuery("SELECT GET_LOCK('" + Id + "', 10)").getSingleResult();
    entityManager.getTransaction().commit();
    return obj_acquire;
}


private Object releaseLock(final EntityManager entityManager, final String Id){

    entityManager.getTransaction().begin();
    Object obj_release = entityManager.createNativeQuery("SELECT RELEASE_LOCK('" + Id + "')").getSingleResult();
    entityManager.getTransaction().commit();
    return obj_release;
}