是否可以动态/在运行时评估包含有效LINQ的字符串?

一定有可能,因为 Linqpad 干吧!

看着 how it works page 这有点让人心烦意乱,我不确定这是否是您想要用生产代码做的事情,除非您真的无法避免它。

没有一种框架方法可以满足您的需求,我可以说,由于.NET的工作方式,它具有相当高的信心。您必须使用 csharpcodeprovider 就像LinqPad一样。

您可能能够更改LINQ动态查询库以执行所需的操作。

我用VB编写了这段代码来计算运行时字符串中包含的代码…您需要将其转换为C,但没有理由不能只传入包含LINQ表达式的字符串。您需要稍微修改functring,以允许使用linq作为我唯一的引用system.math。我在运行时使用它来评估(主要是数学)表达式,但我认为它可以被修改/扩展来评估.NET框架中的几乎所有内容…

Function Evaluate(ByVal Expression As String, ByVal Args() As Object) As Object

    If Expression.Length > 0 Then

        'Replace each parameter in the calculation expression with the correct values
        Dim MatchStr = "{(\d+)}"
        Dim oMatches = Regex.Matches(Expression, MatchStr)
        If oMatches.Count > 0 Then
            Dim DistinctCount = (From m In oMatches _
                                 Select m.Value).Distinct.Count
            If DistinctCount = Args.Length Then
                For i = 0 To Args.Length - 1
                    Expression = Expression.Replace("{" & i & "}", Args(i))
                Next
            Else
                Throw New ArgumentException("Invalid number of parameters passed")
            End If
        End If

        Dim FuncName As String = "Eval" & Guid.NewGuid.ToString("N")
        Dim FuncString As String = "Imports System.Math" & vbCrLf & _
                                   "Namespace EvaluatorLibrary" & vbCrLf & _
                                   "  Class Evaluators" & vbCrLf & _
                                   "    Public Shared Function " & FuncName & "() As Double" & vbCrLf & _
                                   "      " & Expression & vbCrLf & _
                                   "    End Function" & vbCrLf & _
                                   "  End Class" & vbCrLf & _
                                   "End Namespace"

        'Tell the compiler what language was used
        Dim CodeProvider As CodeDomProvider = CodeDomProvider.CreateProvider("VB")

        'Set up our compiler options...
        Dim CompilerOptions As New CompilerParameters()
        With CompilerOptions
            .ReferencedAssemblies.Add("System.dll")
            .GenerateInMemory = True
            .TreatWarningsAsErrors = True
        End With

        'Compile the code that is to be evaluated
        Dim Results As CompilerResults = _
            CodeProvider.CompileAssemblyFromSource(CompilerOptions, FuncString)

        'Check there were no errors...
        If Results.Errors.Count > 0 Then
        Else
            'Run the code and return the value...
            Dim dynamicType As Type = Results.CompiledAssembly.GetType("EvaluatorLibrary.Evaluators")
            Dim methodInfo As MethodInfo = dynamicType.GetMethod(FuncName)
            Return methodInfo.Invoke(Nothing, Nothing)
        End If

    Else
        Return 0

    End If

    Return 0

End Function

Sub Main()
    'In a real application, this string would be loaded from a database
    'it would be stored by some calculation administrator...
    Dim Expr As String = "  If ({0} < 20000) Then" & vbCrLf & _
                         "    Return Max(15, Min(75,0.12*{0}))" & vbCrLf & _
                         "  Else" & vbCrLf & _
                         "    Return Max(75,0.05*{0})" & vbCrLf & _
                         "  End If"

    Dim Args As New List(Of String)
    While True
        'This value would be loaded from some data interpreter for inclusion
        'in the calculation...
        Dim Val As String = Console.ReadLine
        Args.Clear()
        If IsNumeric(Val) Then
            Args.Add(Val)
            Dim dblOut As Object = Evaluate(Expr, Args.ToArray)
            Console.WriteLine(dblOut)
        Else
            Exit While
        End If
    End While

End Sub

您没有理由不能稍微修改函数定义,这样它就可以作为字符串的扩展来运行,从而允许您这样调用它:

Dim LinqString = "from c in myLinqData where c.SomeField.Equals(""somevalue"") select c"
Dim output = LinqString.Evaluate

大部分 LinqToXml 无论如何都是由字符串驱动的。例如, Elements extension method 将获取一个字符串并查找具有该名称的所有子元素。

如果您的查询以字符串开始(而不是以可查询/可枚举的方法调用开始),那么它实际上不是一个LINQ查询,而是其他查询。也许吧 XPath 可以帮忙。