Question

我有一个像这样的工作查询：

SELECT this_.ID, this_.NomeFile, this_.DataGenerazioneFile, esitiopera_.ID, esitiopera_.Date, esitiopera_.ID_FileTelematico
FROM FileTelematico this_ 
LEFT OUTER JOIN EsitoOperazione esitiopera_ ON this_.ID = esitiopera_.ID_FileTelematico 
WHERE SUBSTRING (this_.NomeFile, 1, LEN(this_.NomeFile)-4)
IN ('filename1', 'filename2', 'filename3')   
ORDER BY this_.DataGenerazioneFile DESC;

我正在尝试用QueryOver编写相同的内容

FileTelematico ft = null;
string[] nomi = {'filename1', 'filename2', 'filename3'}
var files = session.QueryOver<FileTelematico>(() => ft)                     
            .Where(() => ft.NomeFile.Substr(1, ft.NomeFile.StrLength() -4)
            .IsIn(nomi))
            .Fetch(x => x.EsitiOperazioni).Eager
            .OrderBy(() => ft.DataGenerazioneFile).Desc
            .List()

但它只是以System.NullReferenceException结束

    in System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
   in System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
   in System.Delegate.DynamicInvokeImpl(Object[] args)
   in System.Delegate.DynamicInvoke(Object[] args)
   in NHibernate.Impl.ExpressionProcessor.FindValue(Expression expression) in d:\Projects\NHibernate\nhibernate-core\src\NHibernate\Impl\ExpressionProcessor.cs:riga 248
   in NHibernate.Impl.ExpressionProcessor.FindMemberProjection(Expression expression) in d:\Projects\NHibernate\nhibernate-core\src\NHibernate\Impl\ExpressionProcessor.cs:riga 258
   in NHibernate.Criterion.RestrictionExtensions.ProcessIsInCollection(MethodCallExpression methodCallExpression) in d:\Projects\NHibernate\nhibernate-core\src\NHibernate\Criterion\RestrictionsExtensions.cs:riga 138
   in NHibernate.Impl.ExpressionProcessor.ProcessCustomMethodCall(MethodCallExpression methodCallExpression) in d:\Projects\NHibernate\nhibernate-core\src\NHibernate\Impl\ExpressionProcessor.cs:riga 662
   in NHibernate.Impl.ExpressionProcessor.ProcessBooleanExpression(Expression expression) in d:\Projects\NHibernate\nhibernate-core\src\NHibernate\Impl\ExpressionProcessor.cs:riga 620
   in NHibernate.Impl.ExpressionProcessor.ProcessExpression(Expression expression) in d:\Projects\NHibernate\nhibernate-core\src\NHibernate\Impl\ExpressionProcessor.cs:riga 671
   in NHibernate.Impl.ExpressionProcessor.ProcessLambdaExpression(LambdaExpression expression) in d:\Projects\NHibernate\nhibernate-core\src\NHibernate\Impl\ExpressionProcessor.cs:riga 676
   in NHibernate.Impl.ExpressionProcessor.ProcessExpression(Expression`1 expression) in d:\Projects\NHibernate\nhibernate-core\src\NHibernate\Impl\ExpressionProcessor.cs:riga 697
   in NHibernate.Criterion.QueryOver`2.Add(Expression`1 expression) in d:\Projects\NHibernate\nhibernate-core\src\NHibernate\Criterion\QueryOver.cs:riga 755
   in NHibernate.Criterion.QueryOver`2.Where(Expression`1 expression) in d:\Projects\NHibernate\nhibernate-core\src\NHibernate\Criterion\QueryOver.cs:riga 362
   in NHibernate.Criterion.QueryOver`2.NHibernate.IQueryOver<TRoot,TSubType>.Where(Expression`1 expression) in d:\Projects\NHibernate\nhibernate-core\src\NHibernate\Criterion\QueryOver.cs:riga 803
   in

如果我不使用Substr但我需要使用它（或子串），这不会发生。

P.S。我正在使用Nhibernate 4.0.3 GA

Answer 1

不幸的是，.SubStr扩展方法的功能不足以处理除常量值之外的任何值作为参数。

幸运的是，您可以使用Projections.SqlFunction并以此方式调用substring方法来解决此问题。您还需要添加一个可以进行减法的函数，因为遗憾的是，您无法使用内置的QueryOver功能进行算术运算。

首先，创建一个包含自定义投影的静态类：

public static class CustomProjections
{
    public static IProjection Subtract(IProjection one, IProjection other)
    {
        return Projections.SqlFunction(
            new VarArgsSQLFunction(NHibernateUtil.Int32, "(", "-", ")"),
            NHibernateUtil.Int32,
            one,
            other);
    }

    public static IProjection SubStr(IProjection prop, IProjection start, IProjection end)
    {
        return Projections.SqlFunction(
            "substring",
            NHibernateUtil.String,
            prop,
            start,
            end);
    }

    public static IProjection Length(IProjection prop)
    {
        return Projections.SqlFunction(
            "length",
            NHibernateUtil.Int32,
            prop);
    }
}

接下来，使用Restrictions.In并使用自定义投影，将Length投影的结果传递给SubStr：

FileTelematico ft = null;

session.QueryOver<FileTelematico>(() => ft)
    .Where(
        Restrictions.In(
            CustomProjections.SubStr(
                Projections.Property(() => ft.NomeFile),
                Projections.Constant(1),
                CustomProjections.Subtract(
                    CustomProjections.Length(
                        Projections.Property(() => ft.NomeFile)),
                        Projections.Constant(4))),
            nomi))
    .Fetch(x => x.EsitiOperazioni).Eager
    .OrderBy(() => ft.DataGenerazioneFile).Desc
    .List();

有点乱，但应该完成工作。

如果您想通过将.Where调用的各个部分重构为变量，可以稍微清理一下：

FileTelematico ft = null;

IProjection length = 
    CustomProjections.Subtract(
        CustomProjections.Length(Projections.Property(() => ft.NomeFile)),
        Projections.Constant(4));

IProjection substring =
    CustomProjections.SubStr(
        Projections.Property(() => ft.NomeFile),
        Projections.Constant(1),
        length);

AbstractCriterion inRestriction =
    Restrictions.In(substring, nomi);


session.QueryOver<FileTelematico>(() => ft)
    .Where(inRestriction)
    .Fetch(x => x.EsitiOperazioni).Eager
    .OrderBy(() => ft.DataGenerazioneFile).Desc
    .List();

Nhibernate子字符串错误

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