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我有个问题。我收到“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，但无济于事： 

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 来休眠。这是堆栈跟踪。谁能解释一下？

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)
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2 回答 2

1

这是一个长期的猜测。

您可以将其添加到您的谓词构建器类的副本中

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());

可能不会解决您的重复键问题 - 我没有看到任何涉及的字典。你在问什么？

于 2011-10-21T01:42:20.200 回答
1

我刚刚在 LINQ to Objects、LINQ to SQL 和 LINQ to Entities 中尝试了您的示例，并且在所有这些中都可以正常工作（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，您必须使用类似 an 的东西复制该树的每个节点ExpressionVisitor，这很麻烦并且可能会或可能不会最终解决您的问题。

根据代码的结构，一种解决方法可能是复制原始表达式树两次，方法是传入首先生成该表达式的任何内容：

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，看起来它可能并不那么困难。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();
于 2011-10-21T02:12:25.607 回答