[Solved] JPA EntityManager find method doesn’t work [closed]

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You can get CustomerMapping by cardId using JPQL. A more optimal solution will be to use projections.

public String getCustomerMappingCustomerId(String cardId) {
    getEntityManager();        
    CustomerMapping result = first(em.createQuery(
        "select c from CustomerMapping c where c.cardId = :cardId")
        .setParameter("cardId", cardId).getResultList());
    return result ==  null ? null : result.getCustomerId(); 
}

private static <T> T first(List<T> items) {
    return items == null || items.isEmpty() ? null : items.get(0);
}

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solved JPA EntityManager find method doesn’t work [closed]