当我向查询添加相同的表达式两次时，为什么会出现此 Linq to Nhibernate 异常？

Question

我有一个问题。我收到一条“已添加具有相同密钥的项目”。当我尝试枚举查询结果时出现异常。当我尝试在最终查询中包含来自同一原始变量的表达式时，就会发生这种情况。我试图通过复制表达式来解决这个问题，但没有成功：

var predicate1 = PredicateBuilder.True<SomeType>();
var predicate2 = PredicateBuilder.True<SomeType>();
var predicate3 = PredicateBuilder.True<SomeType>();   


    System.Linq.Expressions.Expression<Func<FieldObservation, bool>> predicate1copy1 =           System.Linq.Expressions.Expression.Lambda<Func<FieldObservation, bool>>(predicate1.Body, predicate1.Parameters);
    System.Linq.Expressions.Expression<Func<FieldObservation, bool>> predicate1copy2 = System.Linq.Expressions.Expression.Lambda<Func<FieldObservation, bool>>(predicate1.Body, predicate1.Parameters);

    predicate2 = x => x.FirstBoolProperty;
    predicate2 = predicate2.And(predicate1copy1); 
    predicate3 = x => x.SecondBoolProperty;
    predicate3 = predicate3.And(predicate1copy2); //predicate1copy2 comes from the same original predicate1
    var predicate4 = predicate2.Or(predicate3);
    var results1 = query.Where(predicate4).ToList(); //exception thrown here: "An item with the same key has already been added."

我正在使用 Linq to Nhibernate。这是堆栈跟踪。谁能解释一下吗？

Stacktrace:
   at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource)
   at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)
   at System.Collections.Generic.Dictionary`2.Add(TKey key, TValue value)
   at NHibernate.Linq.Visitors.ExpressionParameterVisitor.VisitConstantExpression(ConstantExpression expression) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Linq\Visitors\ExpressionParameterVisitor.cs:line 43
   at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitExpression(Expression expression) in :line 0
   at NHibernate.Linq.Visitors.NhExpressionTreeVisitor.VisitExpression(Expression expression) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Linq\Visitors\NhExpressionTreeVisitor.cs:line 32
   at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitBinaryExpression(BinaryExpression expression) in :line 0
   at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitExpression(Expression expression) in :line 0
   at NHibernate.Linq.Visitors.NhExpressionTreeVisitor.VisitExpression(Expression expression) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Linq\Visitors\NhExpressionTreeVisitor.cs:line 32
   at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitBinaryExpression(BinaryExpression expression) in :line 0
   at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitExpression(Expression expression) in :line 0
   at NHibernate.Linq.Visitors.NhExpressionTreeVisitor.VisitExpression(Expression expression) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Linq\Visitors\NhExpressionTreeVisitor.cs:line 32
   at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitLambdaExpression(LambdaExpression expression) in :line 0
   at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitExpression(Expression expression) in :line 0
   at NHibernate.Linq.Visitors.NhExpressionTreeVisitor.VisitExpression(Expression expression) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Linq\Visitors\NhExpressionTreeVisitor.cs:line 32
   at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitUnaryExpression(UnaryExpression expression) in :line 0
   at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitExpression(Expression expression) in :line 0
   at NHibernate.Linq.Visitors.NhExpressionTreeVisitor.VisitExpression(Expression expression) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Linq\Visitors\NhExpressionTreeVisitor.cs:line 32
   at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitAndConvert[T](T expression, String methodName) in :line 0
   at Remotion.Linq.Parsing.ExpressionTreeVisitor.<>c__DisplayClass6`1.<VisitAndConvert>b__5(T expression) in :line 0
   at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitList[T](ReadOnlyCollection`1 list, Func`2 visitMethod) in :line 0
   at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitAndConvert[T](ReadOnlyCollection`1 expressions, String callerName) in :line 0
   at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitMethodCallExpression(MethodCallExpression expression) in :line 0
   at Remotion.Linq.Parsing.ExpressionTreeVisitor.VisitExpression(Expression expression) in :line 0
   at NHibernate.Linq.Visitors.NhExpressionTreeVisitor.VisitExpression(Expression expression) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Linq\Visitors\NhExpressionTreeVisitor.cs:line 32
   at NHibernate.Linq.Visitors.ExpressionParameterVisitor.Visit(Expression expression) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Linq\Visitors\ExpressionParameterVisitor.cs:line 21
   at NHibernate.Linq.NhLinqExpression..ctor(Expression expression) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Linq\NhLinqExpression.cs:line 38
   at NHibernate.Linq.DefaultQueryProvider.PrepareQuery(Expression expression, IQuery& query, NhLinqExpression& nhQuery) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Linq\DefaultQueryProvider.cs:line 67
   at NHibernate.Linq.DefaultQueryProvider.Execute(Expression expression) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Linq\DefaultQueryProvider.cs:line 33
   at NHibernate.Linq.DefaultQueryProvider.Execute[TResult](Expression expression) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Linq\DefaultQueryProvider.cs:line 40
   at Remotion.Linq.QueryableBase`1.GetEnumerator() in :line 0
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at FieldSystemCore.Reports.ObservationReport.ObservationReportSearch.getResults(ObservationReportConfigurationObject config) in C:\Users\Isaac.G\Desktop\checkout\Field System\FieldSystem\FieldSystemCore\Reports\ObservationReport\ObservationReportSearch.cs:line 39
   at FieldSystemGUI.Controls.Reports.ObservationReport.ObservationReport_ReportSearchEvent(Object sender, DoWorkEventArgs e) in C:\Users\Isaac.G\Desktop\checkout\Field System\FieldSystem\FieldSystemGUI\Controls\Reports\ObservationReport.cs:line 99
   at GUIComponents.Controls.Reports.BaseCommonReport.backgroundWorker_DoWork(Object sender, DoWorkEventArgs e) in C:\Users\Isaac.G\Desktop\checkout\Library Projects\GUIComponents\GUIComponents\Controls\Reports\BaseCommonReport.cs:line 194
   at System.ComponentModel.BackgroundWorker.OnDoWork(DoWorkEventArgs e)
   at System.ComponentModel.BackgroundWorker.WorkerThreadStart(Object argument)

Answer 1

我刚刚在 LINQ to Objects、LINQ to SQL 和 LINQ to Entities 中尝试了您的示例，它在所有这些示例中都运行良好（只需稍作调整）。您可能希望将其作为错误报告给 LINQ to NHibernate 团队。

为了“复制”表达式树，您必须使用 ExpressionVisitor，这很麻烦，可能会也可能不会解决您的问题。

根据代码的结构方式，一种解决方法可能是通过传入首先生成该表达式的任何内容来重现原始表达式树两次：

Func<Expression<Func<SomeType, bool>>> predicate1Builder = 
    () => PredicateBuilder.True<SomeType>();

var predicate2 = PredicateBuilder.True<SomeType>();
var predicate3 = PredicateBuilder.True<SomeType>();    

predicate2 = x => x.FirstBoolProperty;
predicate2 = predicate2.And(predicate1Builder());
predicate3 = x => x.SecondBoolProperty;
predicate3 = predicate3.And(predicate1Builder()); 
var predicate4 = predicate2.Or(predicate3);
var results1 = query.Where(predicate4).ToList(); 

更新

我刚刚花了一些时间阅读 ExpressionVisitors，看起来可能不会毕竟有那么困难。看看这是否有效：

public class Visitor : ExpressionVisitor
{
    public Expression<T> Modify<T>(Expression<T> node) {return (Expression<T>)Visit(node);}
}

var predicate1 = PredicateBuilder.True<SomeType>();
var predicate2 = PredicateBuilder.True<SomeType>();
var predicate3 = PredicateBuilder.True<SomeType>();    

predicate2 = x => x.FirstBoolProperty;
predicate2 = predicate2.And(predicate1);
predicate3 = x => x.SecondBoolProperty;
var copy = new Visitor().Modify(predicate1);
predicate3 = predicate3.And(copy); 
var predicate4 = predicate2.Or(predicate3);

var results1 = query.Where(predicate4).ToList(); 

Answer 2

这是一个不太可能的猜测。

您可以将其添加到 predicatebuilder 类的副本中

public static Expression<Func<T, bool>> Copy<T>
  (this Expression<Func<T, bool>> expr1)
{
  return Expression.Lambda<Func<T, bool>>(expr1.Body, expr1.Parameters);
}

，然后像这样使用它：

predicate3 = predicate3.And(predicate1.Copy());

可能赢了无法解决您的重复密钥问题 - 我没有看到任何涉及的词典。你在查询什么？