NHibernate 将 sql 查询转换为 NHibernate QueryOver 查询

Question

所以我有一点 SQL 查询，我不确定如何转换为 NHibernate 语法

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

我目前有以下 NHibernate 代码：

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

如您所见，我不确定如何执行* -1部分？ 有人知道怎么做吗？

Answer 1

您可以使用SQLFunctionTemplate和Projections.SqlFunction来表达任何需要投影参数的复杂 SQL。 在您的情况下，您可以执行以下操作：

    //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
        );