NHibernate 將 sql 查詢轉換為 NHibernate QueryOver 查詢

Question

所以我有一點 SQL 查詢，我不確定如何轉換為 NHibernate 語法

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 代碼：

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

如您所見，我不確定如何執行* -1部分？ 有人知道怎么做嗎？

Answer 1

您可以使用SQLFunctionTemplate和Projections.SqlFunction來表達任何需要投影參數的復雜 SQL。 在您的情況下，您可以執行以下操作：

    //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
        );