Using Queries

The RequestBean.adjustOrderDiscount business method updates the discount applied to all orders. This method uses the findAllOrders named query, defined in Order:

@NamedQuery(
    name="findAllOrders",
    query="SELECT o FROM Order o"
)

The EntityManager.createNamedQuery method is used to run the query. Because the query returns a List of all the orders, the Query.getResultList method is used.

List orders = em.createNamedQuery(
    "findAllOrders")
    .getResultList();

The RequestBean.getTotalPricePerVendor business method returns the total price of all the parts for a particular vendor. This method uses a named parameter, id, defined in the named query findTotalVendorPartPricePerVendor defined in VendorPart.

@NamedQuery(
    name="findTotalVendorPartPricePerVendor",
    query="SELECT SUM(vp.price) " +
    "FROM VendorPart vp " +
    "WHERE vp.vendor.vendorId = :id"
)

When running the query, the Query.setParameter method is used to set the named parameter id to the value of vendorId, the parameter to RequestBean.getTotalPricePerVendor:

return (Double) em.createNamedQuery(
    "findTotalVendorPartPricePerVendor")
    .setParameter("id", vendorId)
    .getSingleResult();

The Query.getSingleResult method is used for this query because the query returns a single value.