带有 JoinAlias 的 Nhibernate QueryOver 上的 TargetInvocationException

Question

Product productAlias = null;
Session sessionAlias = null;
Slot slotAlias = null;
Price priceAlias = null;

var queryOver = session.QueryOver<Slot>(() => slotAlias)
    .JoinAlias(() => slotAlias.Session, () => sessionAlias)
    .JoinAlias(() => sessionAlias.Product, () => productAlias);

if (productGuid.HasValue)
{
    var productEntity = session.Query<Product>().FirstOrDefault(x => x.Guid == productGuid.Value);
    queryOver = queryOver.Where(() => productAlias.Id == productEntity.Id);
}

if (onlyAvailable)
{
    queryOver = queryOver.Where(() => slotAlias.StartDate >= DateTimeOffset.UtcNow.AddMinutes(productAlias.Duration));
}

queryOver.List();

当我运行这个查询时，我得到 TargetInvocationException。在内部消息中，它是 slotAlias.StartDate 处的 NullReferenceException（第 18 行，在 onlyAvailable if 子句内）。

像这样在 if 子句和多个 Where 子句中使用别名有问题吗？

堆栈跟踪：

System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at lambda_method(Closure )
   --- End of inner exception stack trace ---
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
   at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
   at System.Delegate.DynamicInvokeImpl(Object[] args)
   at NHibernate.Impl.ExpressionProcessor.FindValue(Expression expression)
   at NHibernate.Impl.ExpressionProcessor.ProcessSimpleExpression(Expression left, Expression right, ExpressionType nodeType)
   at NHibernate.Impl.ExpressionProcessor.ProcessSimpleExpression(BinaryExpression be)
   at NHibernate.Impl.ExpressionProcessor.ProcessBinaryExpression(BinaryExpression expression)
   at NHibernate.Impl.ExpressionProcessor.ProcessExpression(Expression expression)
   at NHibernate.Criterion.QueryOver`2.NHibernate.IQueryOver<TRoot,TSubType>.Where(Expression`1 expression)
   at Fullseats.Database.Repositories.Repository.GetSlots(Int32 limit, Int32 offset, Nullable`1 operatorGuid, Nullable`1 productGuid, Nullable`1 from, Nullable`1 to, Boolean onlyAvailable) in C:\Users\erkin\Desktop\FullSeats\Fullseats.Api\Fullseats.Database\Repositories\Repository.cs:line 455
   at Fullseats.Server.Core.Services.ProductService.GetSlots(Guid productGuid, PaginationQuery paginationQuery) in C:\Users\erkin\Desktop\FullSeats\Fullseats.Api\Fullseats.Server\Core\Services\ProductService.cs:line 63
   at Fullseats.Server.Modules.ProductModule.GetSlotsForProduct(Object arg) in C:\Users\erkin\Desktop\FullSeats\Fullseats.Api\Fullseats.Server\Modules\ProductModule.cs:line 224
   at CallSite.Target(Closure , CallSite , Func`2 , Object )
   at System.Dynamic.UpdateDelegates.UpdateAndExecute2[T0,T1,TRet](CallSite site, T0 arg0, T1 arg1)
   at Nancy.Routing.Route.<>c__DisplayClass4.<Wrap>b__3(Object parameters, CancellationToken context)

Answer 1

这一行：

queryOver.Where(
    () => slotAlias.StartDate >= DateTimeOffset.UtcNow.AddMinutes(productAlias.Duration));

您实际上是在将应用程序端逻辑与数据库端逻辑混合在一起。 DateTimeOffset.UtcNow.AddMinutes 在 之前执行 查询被发送到数据库。这就是为什么传递常量值而不是 productAlias.Duration 起作用的原因。

由于您没有将预定义值作为参数发送，因此您需要在数据库中执行日期操作。

执行此操作可能需要几个步骤，具体取决于您的方言。我将假设 SQL Server 2012。

使用定义 addminutes 函数的函数创建自定义方言：

public class MyDialect : MsSql2012Dialect
{
    public MyDialect()
    {
        this.RegisterFunction(
            "addminutes",
            new SQLFunctionTemplate(NHibernateUtil.DateTimeOffset, "dateadd(n, ?1, ?2)"));
    }
}

在您的查询中使用新注册的函数：

queryOver = queryOver.Where(
    Restrictions.GeProperty(
        Projections.Property(() => slotAlias.StartDate),
        Projections.SqlFunction(
            "addminutes",
            NHibernateUtil.DateTimeOffset,
            Projections.Property(() => productAlias.Duration),
            Projections.Constant(DateTimeOffset.UtcNow))))

这会生成一个 SQL 片段，如下所示：

WHERE
    slotAlia_1.StartDate >= dateadd(minute, this_.Duration, '8/9/2016 2:22:48 AM +00:00');

C# 可能有点难读，您可以重构 SqlFunction 部分：

var addMinutesFunction = Projections.SqlFunction(
    "addMinutes",
    NHibernateUtil.DateTimeOffset,
    Projections.Property(() => productAlias.Duration),   
    Projections.Constant(DateTimeOffset.UtcNow))

queryOver = queryOver.Where(
    Restrictions.GeProperty(
        Projections.Property(() => slotAlias.StartDate), addMinutesFunction))

带有 JoinAlias 的 Nhibernate QueryOver 上的 TargetInvocationException

TargetInvocationException on Nhibernate QueryOver with JoinAlias

nhibernate

queryover