How to use case and order in Nhibernate?

Question

I need to order the result in the DB table ChargeOperationsin my own direction on typeId. The SQL query is as follows:

SELECT * FROM ChargeOperations co
LEFT JOIN ShadowChargeOperations sco ON sco.ChargeOperationId=co.Id
-- just exclude some extra data.
WHERE sco.Id IS NULL
ORDER BY
 CASE co.TypeId
  WHEN 1 THEN 3   -- this is my order, which is different from id of type and can change
  WHEN 2 THEN 1
  WHEN 3 THEN 2
  ELSE 4
 END,
 co.TypeId,
 co.CalculationAmount

So, please, can you give me an example of how I can create this construct.

CASE co.TypeId 
  WHEN 1 THEN 3   -- this is my order, which is different from id of type and can change
  WHEN 2 THEN 1
  WHEN 3 THEN 2
  ELSE 4

with QueryOver.

Answer 1

You can do this using Projections.Conditional, for sample:

ChargeOperation itemAlias = null;

var result = 
    session.QueryOver<ChargeOperation>(() => itemAlias)
            .Where ( /*your conditions*/)
            .OrderBy(Projections.Conditional(
                        Restrictions.Where(() => itemAlias.TypeId == 1),
                        Projections.Constant(3),                                
                    Projections.Conditional(
                        Restrictions.Where(() => itemAlias.TypeId == 2),
                        Projections.Constant(1),
                    Projections.Conditional(
                        Restrictions.Where(() => itemAlias.TypeId == 3),
                        Projections.Constant(2),
                        )
                    )           
                )                           
            ).Asc
            .ThenBy(x => x.TypeId)
            .ThenBy(x => x.CalculationAmount)
        .List();