HQL - unusual queries

Question

Using Northwind database I would like to make queries like

• Number of orders from each Customer.Country
• What is the sum of OrderDetails.UnitPrice for every day of week
• Average time from Order.RequiredDate to Order.ShippedDate each year
• ... more queries like these

I have to use hibernate to obtain the result, but I have strong feeling that it is pointless. Now I use createSQLQuery() because I can easily get result using SQL.

But how to do this using HQL? Could you please give me any example? I think using HQL isn't exactly the most resonable, but I would like to know how it can be done.

[Edit]

For example, can query:

select avg(DATEDIFF(ShippedDate, OrderDate)), year(ShippedDate) from orders group by year(ShippedDate)

be translated to HQL? or Should I get all Orders first and calculate result myself in my application?

or

select CompanyName, year(ShippedDate), sum(UnitPrice)/sum(Quantity) from shippers inner join orders on ShipperID = ShipVia inner join orderdetails on orderdetails.OrderID = orders.OrderID group by CompanyName, year(ShippedDate)

If I don't ask for set of object like Order or Shipper, can I use HQL?

I've seen a lot of tutorials, but they all refer to "objective oriented" queries. Could you please show me the way to translate to HQL these "unusual" queries?

Answer 1

How are these "unusual" queries? These are exactly the kinds of queries that show why RDBMS is still around. Unfortunately you do not show your mappings, so I will make a few assumptions... Looking at some of your bullets:

First, Number of orders from each Customer.Country. I will assume you have mapped Order->Customer as a @ManyToOne association

List results = session.createQuery( "select c.country, count(o.id) from Order o join o.customer c" ).list();
Object[] result = (Object[]) results.get( 0 );
print( "Country : " + result[0] );
print( "Number of Orders : " + result[1] );

or how about assuming a wrapper (OO!) for the results:

List results = session.createQuery( "select new CountryOrderCount( c.country, count(o.id) ) from Order o join o.customer c" ).list();
CountryOrderCount result = (CountryOrderCount) results.get( 0 );
print( "Country : " + result.getCountry() );
print( "Number of Orders : " + result.getOrderCount() );

What is the sum of OrderDetails.UnitPrice for every day of week. I will assume you have OrderDetails->Order mapped and that "day of the week" refers to Order.OrderDate:

List results = session.createQuery( "select dayOfWeek(o.orderDate), sum(od.unitPrice) from OrderDetails od join od.order o group by dayOfWeek(o.orderDate)" ).list();
...

One thing to note about the above is the use of a function. This might translate directly into a database function, but is mapped through function templates mapped with the Hibernate Dialect. For additional info, see http://docs.jboss.org/hibernate/orm/4.3/javadocs/org/hibernate/dialect/function/package-summary.html or http://docs.jboss.org/hibernate/orm/4.3/manual/en-US/html_single/#portability-functions