Nhibernate计数不同(基于多列)

Question

基本上,我一直在尝试这样做(根据两列计算不同):

select count(distinct(checksum(TableA.PropertyA, TableB.PropertyB))) 
from TableA 
left outer join TableB
on TableA.TableBId = TableB.Id 
where PropertyA like '%123%'

谷歌搜索如何做到这一点,但没有运气.试过这个,但从未真正奏效过.这并不明显基于两个表中的两个属性:

var queryOver = c.QueryOver<TableA>();
TableB tableBAlias = null;
TableA tableAAlias = null;
ProjectionList projections = Projections.ProjectionList();

queryOver.AndRestrictionOn(x => x.PropertyA).IsLike("%123%");
projections.Add(Projections.CountDistinct(() => tableAAlias.PropertyA));

queryOver.JoinAlias(x => x.TableB , () => tableBAlias, JoinType.LeftOuterJoin);
projections.Add(Projections.CountDistinct(() => tableBAlias.PropertyB));

queryOver.Select(projections);
queryOver.UnderlyingCriteria.SetProjection(projections);
return queryOver.TransformUsing(Transformers.DistinctRootEntity).RowCount();

Answer 1

好的,这需要几步,所以请耐心等待.我在这里假设SQL服务器,但是指令应该适用于任何支持checksum^1的方言:

1. 创建支持该checksum功能的自定义方言:

   public class MyCustomDialect : MsSql2008Dialect
   {
       public MyCustomDialect()
       {
           RegisterFunction("checksum", new SQLFunctionTemplate(NHibernateUtil.Int32, "checksum(?1, ?2)"));
       }
   }
   

2. 更新您的配置以使用自定义方言(您可以在配置XML文件中或使用代码执行此操作.有关详细信息,请参阅此答案).以下是我在现有配置代码中的使用方法:

   configuration
       .Configure(@"hibernate.cfg.xml")
       .DataBaseIntegration(
           db => db.Dialect<MyCustomDialect>());
   

3. 创建一个调用的自定义投影checksum.这一步是可选的 - Projections.SqlFunction如果您愿意,可以直接调用,但我认为将其重构为一个单独的函数更简洁:

   public static class MyProjections 
   {
       public static IProjection Checksum(params IProjection[] projections)
       {
           return Projections.SqlFunction("checksum", NHibernateUtil.Int32, projections);   
       }
   }
   

4. 编写QueryOver查询并调用自定义投影:

   int count = session.QueryOver<TableA>(() => tableAAlias)
       .Where(p => p.PropertyA.IsLike("%123%"))
       .Left.JoinQueryOver(p => p.TableB, () => tableBAlias)
       .Select(
           Projections.Count(
               Projections.Distinct(
               MyProjections.Checksum(
                   Projections.Property(() => tableAAlias.PropertyA),
                   Projections.Property(() => tableBAlias.PropertyB)))))
       .SingleOrDefault<int>();
   

   这应该生成看起来像你所追求的SQL:

   SELECT count(distinct checksum(this_.PropertyA, tableba1_.PropertyB)) as y0_
   FROM   [TableA] this_
       left outer join [TableB] tableba1_
       on this_.TableBId = tableba1_.Id
   WHERE  this_.PropertyA like '%123%' /* @p0 */
   

¹仍然试图弄清楚是否有一种方法来映射函数而无需手动指定参数的数量