列出使用连接多个表达式构建表达式树时的异常

本文关键字：表达式 构建 异常 连接 | 更新日期: 2023-09-27 18:02:37

我正在构建一个例程来连接几个实体，以便按字符串进行过滤。我使用下面的代码创建表达式，它可以正常工作，因为我使用相同的代码进行排序。

private void SetExpression<T>(string property, ref Type type, ref ParameterExpression arg, ref Expression expr)
{
    string[] props = property.Split('.');
    foreach (string prop in props)
    {
        PropertyInfo pi = type.GetProperty(prop);
        expr = Expression.Property(expr, pi);
        type = pi.PropertyType;
    }
}

然后我使用另外两种方法来构建树。我使用GenerateConcat来创建连接部分。

private Expression<Func<T, string>> GenerateConcat(ParameterExpression parameterExpression, params Expression[] expressions)
{
    var parameter = parameterExpression;
    var separator = Expression.Constant(" ");
    var concatArgs = expressions;
    var concatCall = Expression.Call(typeof(string).GetMethod("Concat", new[] { typeof(string), typeof(string), typeof(string) }), concatArgs);
    return Expression.Lambda<Func<T, string>>(concatCall, parameter);
}

我使用generatcontains来创建contains方法。

private Expression<Func<T, bool>> GenerateContains(Expression<Func<T, string>> member, string value)
{
    var containsCall = Expression.Call(member.Body, "Contains", Type.EmptyTypes, Expression.Constant(value));
    return Expression.Lambda<Func<T, bool>>(containsCall, member.Parameters);
}

当运行时，一切看起来都很好，我的谓词看起来是正确的。然而，当调用ToList()时，会抛出以下异常。

System.InvalidOperationException: The parameter 'x' was not bound in the specified LINQ to Entities query expression.
Result StackTrace:  
at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.ParameterTranslator.TypedTranslate(ExpressionConverter parent, ParameterExpression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MemberAccessTranslator.TypedTranslate(ExpressionConverter parent, MemberExpression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MemberAccessTranslator.TypedTranslate(ExpressionConverter parent, MemberExpression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.StringTranslatorUtil.ConvertToString(ExpressionConverter parent, Expression linqExpression)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.StringTranslatorUtil.<>c__DisplayClass1c.<ConcatArgs>b__1a(Expression arg)
   at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
   at System.Linq.Buffer`1..ctor(IEnumerable`1 source)
   at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.StringTranslatorUtil.ConcatArgs(ExpressionConverter parent, Expression linq, Expression[] linqArgs)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.StringConcatTranslator.Translate(ExpressionConverter parent, MethodCallExpression call)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.TypedTranslate(ExpressionConverter parent, MethodCallExpression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateFunctionIntoLike(MethodCallExpression call, Boolean insertPercentAtStart, Boolean insertPercentAtEnd, Func`5 defaultTranslator)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.StringContainsTranslator.Translate(ExpressionConverter parent, MethodCallExpression call)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.TypedTranslate(ExpressionConverter parent, MethodCallExpression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.BinaryTranslator.TypedTranslate(ExpressionConverter parent, BinaryExpression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.BinaryTranslator.TypedTranslate(ExpressionConverter parent, BinaryExpression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateLambda(LambdaExpression lambda, DbExpression input)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateLambda(LambdaExpression lambda, DbExpression input, DbExpressionBinding& binding)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.OneLambdaTranslator.Translate(ExpressionConverter parent, MethodCallExpression call, DbExpression& source, DbExpressionBinding& sourceBinding, DbExpression& lambda)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.OneLambdaTranslator.Translate(ExpressionConverter parent, MethodCallExpression call)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.SequenceMethodTranslator.Translate(ExpressionConverter parent, MethodCallExpression call, SequenceMethod sequenceMethod)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.TypedTranslate(ExpressionConverter parent, MethodCallExpression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.Convert()
   at System.Data.Entity.Core.Objects.ELinq.ELinqQueryState.GetExecutionPlan(Nullable`1 forMergeOption)
   at System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClass7.<GetResults>b__6()
   at System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction[T](Func`1 func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess)
   at System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClass7.<GetResults>b__5()
   at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute[TResult](Func`1 operation)
   at System.Data.Entity.Core.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption)
   at System.Data.Entity.Core.Objects.ObjectQuery`1.<System.Collections.Generic.IEnumerable<T>.GetEnumerator>b__0()
   at System.Data.Entity.Internal.LazyEnumerator`1.MoveNext()
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at Triton.Repository.Test.UnitTest1.ComplexTypeTest() in C:'BitBucket'triton-mvc-5'Triton'Triton.Repository.Test'UnitTest1.cs:line 56
Result Message: 
Test method Triton.Repository.Test.UnitTest1.ComplexTypeTest threw exception: 
System.InvalidOperationException: The parameter 'x' was not bound in the specified LINQ to Entities query expression.

我猜，但问题是我如何构建Concat部分(GenerateConcat)，但我似乎无法找出什么是错的。我是否错过了关于ParameterExpression的任何东西?我确保所有的表达式都是一样的。提前感谢。

编辑1:下面是创建表达式 的代码

我使用Initialize块创建基于属性名的表达式。然后我使用Append方法从其他属性中获取表达式。我的错误是当我创建子属性时，我没有正确地分配ParameterExpression。因此，我重载了initialize并添加了ParamerterExpression参数，以保持所有子属性的表达式相同。这就解决了。

public ExpressionBuilder Initialize<T>(string property)
{
    if (string.IsNullOrEmpty(property))
        throw new ArgumentNullException(property);
    Type type = typeof(T);
    ParameterExpression arg = Expression.Parameter(type, "x");
    Expression expr = arg;
    SetExpression<T>(property, ref type, ref arg, ref expr);
    ExpressionModel = new ExpressionModel() { Expression = expr, ParameterExpression = arg, Type = type };
    IsIntialized = true;
    return this;
}

public ExpressionBuilder Append<T>(string property)
{
    if (string.IsNullOrEmpty(property))
        throw new ArgumentNullException(property);
    if (IsIntialized == false)
        throw new Exception("ExpressionBuilder has not been initialized.");
    Type type = ExpressionModel.Type;
    ParameterExpression arg = ExpressionModel.ParameterExpression;
    Expression expr = ExpressionModel.Expression;
    SetExpression<T>(property, ref type, ref arg, ref expr);
    ExpressionModel.Expression = expr;
    ExpressionModel.ParameterExpression = arg;
    ExpressionModel.Type = type;
    return this;
}

列出使用连接多个表达式构建表达式树时的异常

子属性的ParameterExpression必须与父属性相同。因此，我重载了创建Expression的函数，以便能够显式地设置ParameterExpression。

public ExpressionBuilder Initialize<T>(string property, ParameterExpression parameterExpression)
{
    if (string.IsNullOrEmpty(property))
        throw new ArgumentNullException(property);
    Type type = typeof(T);
    ParameterExpression arg = parameterExpression;
    Expression expr = arg;
    SetExpression<T>(property, ref type, ref arg, ref expr);
    ExpressionModel = new ExpressionModel() { Expression = expr, ParameterExpression = arg, Type = type };
    IsIntialized = true;
    return this;
}
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