NHibernate transform sql query to NHibernate QueryOver query

Question

So I have a bit of a SQL query which I am not sure how to convert to NHibernate syntax

cast(case when count(distinct order) > 1 then count(distinct order) * -1 else max(order.orderId) end as int)

I currently have the following NHibernate code:

projectionList.Add(
    Projections.Conditional(
        Restrictions.Gt(Projections.CountDistinct(() => orderDto), 1),
            Projections.CountDistinct(() => orderDto), // TODO: * -1
            Projections.Max(() => orderDto.orderId)
    )
);

As you can see, I am not sure how to do the * -1 part? Has somebody any idea how to do it?

Roman Artiukhin · Accepted Answer · 2020-07-23 09:04:39Z

1

You can use SQLFunctionTemplate and Projections.SqlFunction to express any complex SQL that needs projection parameters. In your case you can do something like this:

    //All projections parameters in template are replaced with placeholders like ?1 ?2 ?3...
    //If possible move it to static field to avoid template parsing on each execution
    var yourTemplate = new SQLFunctionTemplate(
        NHibernateUtil.Int32, //Template result
        "cast(case when ?1 > 1 then ?1 * -1 else ?2 end as int)");

    //And in you query use the following projection:
    Projections.SqlFunction(
        yourTemplate,
        null, 
        Projections.CountDistinct(() => orderDto), //?1 in template
        Projections.Max(() => orderDto.orderId) //?2 in template
        );

edited Jul 23, 2020 at 9:04

answered Jul 23, 2020 at 8:53

Roman Artiukhin

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