ToList 在使用连接多个表达式构建表达式树时抛出异常

Question

我正在构建一个例程来连接多个实体以便按字符串进行过滤。我使用以下代码创建我的表达式，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;
    }
}

然后我又使用了 2 种方法来构建树。我使用 GenerateConcat 来制作连接部分。

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 GenerateContains 创建包含方法。

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，一切都很好，我的谓词看起来像是正确形成的。但是，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)，但我似乎无法弄清楚哪里出了问题。关于 ParameterExpression，我是否遗漏了什么？我确保所有表达式都相同。提前致谢。

编辑 1：这是创建表达式的代码

我使用 Initialize 块创建基于属性名称的表达式。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没有正确分配 ParameterExpression。因此，我重载了 Initialize 并添加了一个 ParamerterExpression 参数，以使所有子属性的表达式保持相同。那解决了。

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;
}

Answer 1

子属性的 ParameterExpression 必须与父属性相同。所以我重载了创建 Expression 的函数，以便能够显式设置 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;
}

ToList 在使用连接多个表达式构建表达式树时抛出异常

ToList thows Exception when building Expression tree using concat multiple Expressions

c#

linq

linq-to-entities

expression-trees