Nhibernate计数不同(基于多个列)

Basically, i have been trying to do this (count distinct based on two columns):

基本上，我一直在尝试这样做(根据两栏分别计算):

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

Been googling on how to do this but with no luck. Tried this, but never actually worked. This does not count distinctly based on the two properties from two tables:

一直在谷歌上搜索如何做这个，但没有运气。试过了，但没有成功。根据两张表的两个属性，这并不算清楚:

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();

1 个解决方案

#1

Okay this is going to take a few steps, so bear with me. I'm assuming SQL server here, but the instructions should work for any dialect that supports checksum¹:

好吧，这将采取一些步骤，请耐心等待。我假设这里是SQL server，但是指令应该适用于任何支持checksum1的方言:

Create a custom dialect that supports the checksum function:

创建支持校验和功能的自定义方言:

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

Update your configuration to use the custom dialect (you can do this either in your configuration XML file or with code. See this answer for more information). Here's how I did it inside of my existing configuration code:

更新您的配置以使用自定义方言(您可以在配置XML文件中或在代码中实现这一点)。更多信息请参见此答案)。以下是我在现有配置代码中的做法:
```
configuration
    .Configure(@"hibernate.cfg.xml")
    .DataBaseIntegration(
        db => db.Dialect<MyCustomDialect>());
```
Create a custom projection that calls checksum. This step is optional-- you can call Projections.SqlFunction directly if you'd like, but I think refactoring it into a separate function is cleaner:

创建一个调用校验和的自定义投影。这一步是可选的——您可以调用投影。如果你愿意的话，可以直接使用SqlFunction，但是我认为将其重构为一个单独的函数是更简洁的:
```
public static class MyProjections 
{
    public static IProjection Checksum(params IProjection[] projections)
    {
        return Projections.SqlFunction("checksum", NHibernateUtil.Int32, projections);   
    }
}
```

Write your QueryOver query and call the custom projection:

编写您的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>();

This should generate SQL that looks like what you're after:

这应该会生成如下所示的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 */

¹Still trying to figure out if there's a way to map a function without manually specifying the number of arguments

#1