Nhibernate where子串错误

Question

我有一个这样的工作查询：

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;

我正在尝试使用 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

结尾

    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 Substring），则不会发生这种情况。

P.S。我正在使用 Nhibernate 4.0.3 GA

Answer 1

不幸的是，.SubStr 扩展方法不够强大，无法处理常量值以外的任何参数。

幸运的是，您可以通过使用 Projections.SqlFunction 并以这种方式调用 substring 方法来解决这个问题。您还需要添加一个可以执行减法的函数，因为不幸的是您不能使用内置的 QueryOver 功能执行算术运算。

首先，创建一个包含您的自定义投影的静态 class：

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，但应该能完成工作。

如果您愿意，可以通过将 .Where 调用的各个部分重构为变量来稍微清理一下：

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();

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