带反射错误的Linq：表达式Linq'；调用&x27；LINQ to实体中不支持节点

我在处理lambda表达式时遇到问题。我正在EF下使用MVC，我试图创建一个“元模型”，每个模型都将继承它，并使用它创建一个使用Linq列出元素的方法

因为这是一个“元模型”，我不知道类的定义

我正在尝试这样做，假设我们有一个模型类“Customer”

但是我希望它是泛型的，所以我传递了一个继承类的属性名，并且我希望能够根据这个属性进行搜索（和排序）

这是我最好的方法：

    Public MustInherit Class BaseBL

    Public Function AutoList(Of T)(conf As ConfigurationBL) As List(Of T)
        Dim items As List(Of T)
        Dim sortParam = Expression.Parameter(GetType(T), "param")
        Dim sortFunc = Expression.Convert(Expression.Property(sortParam, conf.SortField), GetType(Object))
        Dim sortExpr = Expression.Lambda(Of Func(Of T, Object))(sortFunc, sortParam).Compile()

        Dim searchFunc As Func(Of T, Boolean) = Function(param)
                                                    Dim prInfo As PropertyInfo = param.GetType.GetProperty(conf.SearchField)
                                                    Dim str As String = prInfo.GetValue(param, Nothing)
                                                    Return str.Contains(conf.SearchText)
                                                End Function

        Dim searchExpr As Expression(Of Func(Of T, Boolean)) = Function(param) searchFunc(param)

        Dim query As IQueryable(Of T) = GetQueryable(Of T)()

        items = query.Where(searchExpr).OrderBy(sortExpr).ToList() '.Skip(conf.PageSize * (conf.PageNumber - 1)).Take(conf.PageSize).ToList()

        Return items
    End Function

    Public MustOverride Function GetQueryable(Of T)() As IQueryable(Of T)
End Class

该类是泛型类T的父类，因此getQuerable（of T）方法将在子类上实现

ConfigurationBL类包含sortField、searchField和searchText，它们将提供正确的配置

这几乎奏效了。我用sortExpr执行orderBy，它可以工作，如果我用searchExpr执行where，它也可以工作

当我试着一起做所有的事情时，问题就来了。它提出了一个例外：

“LINQ to实体中不支持表达式LINQ‘Invoke’节点”

我很确定这是因为我使用

Dim searchExpr As Expression(Of Func(Of T, Boolean)) = Function(param) searchFunc(param)

而不是正确的表达式树，但我不知道如何将searchFunc转换为表达式树

---

我真的很坚持这一点，我真的非常感谢任何帮助和想法，谢谢：）

最后我能够自己修复它，我用这个替换了searchExpr

Dim searchExpr = getSearchExpression(Of T)(conf.SearchField, conf.SearchText).Compile()

在哪里

Private Function getSearchExpression(Of T)(propName As String, search As String) As Expression(Of Func(Of T, Boolean))
        Dim element As ParameterExpression = Expression.Parameter(GetType(T), "element")
        Dim propertyValue As ParameterExpression = Expression.Variable(GetType(String), "propertyValue")
        Dim searchText As ParameterExpression = Expression.Variable(GetType(String), "searchText")

        Dim asgPropertyValue As Expression = Expression.Assign(propertyValue,
            Expression.Convert(Expression.Property(element, propName), GetType(String))
        )

        Dim asgSearchText As Expression = Expression.Assign(searchText,
           Expression.Constant(search)
           )

        Dim callContains As Expression = Expression.Call(propertyValue, GetType(String).GetMethod("Contains"), searchText)


        Dim block As Expression = Expression.Block(GetType(Boolean),
                                   New List(Of ParameterExpression)({propertyValue, searchText}),
                                   asgPropertyValue,
                                   asgSearchText,
                                   callContains
                               )      

        Return Expression.Lambda(Of Func(Of T, Boolean))(block, element)
    End Function

我希望这可以帮助一些人，问候：）

Private Function getSearchExpression(Of T)(propName As String, search As String) As Expression(Of Func(Of T, Boolean))
        Dim element As ParameterExpression = Expression.Parameter(GetType(T), "element")
        Dim propertyValue As ParameterExpression = Expression.Variable(GetType(String), "propertyValue")
        Dim searchText As ParameterExpression = Expression.Variable(GetType(String), "searchText")

        Dim asgPropertyValue As Expression = Expression.Assign(propertyValue,
            Expression.Convert(Expression.Property(element, propName), GetType(String))
        )

        Dim asgSearchText As Expression = Expression.Assign(searchText,
           Expression.Constant(search)
           )

        Dim callContains As Expression = Expression.Call(propertyValue, GetType(String).GetMethod("Contains"), searchText)


        Dim block As Expression = Expression.Block(GetType(Boolean),
                                   New List(Of ParameterExpression)({propertyValue, searchText}),
                                   asgPropertyValue,
                                   asgSearchText,
                                   callContains
                               )      

        Return Expression.Lambda(Of Func(Of T, Boolean))(block, element)
    End Function