Question

我正在使用Dynamic Linq来执行针对LINQ的T-SQL where子句。除了尝试转换我手动尝试使用我在帖子末尾包含的函数转换的LIKE语句时，这很有用。代码甚至不是很完美，但当我意识到在测试过程中会出现错误时，我就停止编程了。执行的代码基本上是这样的：

“trx_no喜欢'％3500％'”

并将其转换为：

“trx_no.Contains（” 3500 “）”

执行此操作：

Dim x = y.Where（“trx_no.Contains（”3500“）”，Nothing）

错误：

“Int32”类型中是否存在适用的方法“包含”？

我认为这个问题是我需要将一个Nullable（Of Int32）的“trx_no”转换为String，所以在经过两天的研究和书籍阅读之后，我想我需要将字符串转换成一个字符串。代表我无法工作的功能。

我也尝试在此链接here中使用Cast，但是这会失败并显示错误：

预期类型'Boolean'的表达式

我的版本看起来像这样：

Dim x = y.Where（“DirectCast（trx_no，System.String）”如'％35000％'“，Nothing）

如果我没有提供足够的代码，我很抱歉，我只是不想让这一点压倒性的。任何建议将不胜感激。谢谢。

`Private Function replaceLike(ByVal str As String) As String
    Dim rtn As String = ""
    If str.ToUpper.Contains(" LIKE '") Then
        Dim firstQuote As Int32 = str.ToUpper.IndexOf(" LIKE '") + 6
        If str.ToUpper.Chars(firstQuote + 1) = Chr(37) Then
            'If the character after the first single quote is a %, this is a Contains or EndsWith
            Dim secondQuote As Int32 = str.ToUpper.IndexOf("'", firstQuote + 1)
            If str.ToUpper.Chars(secondQuote - 1) = Chr(37) Then
                'Handles '%%', '%value%', '%'
                'Found % before the last quote, this is a Contains or has the value of '%'.
                Dim val = ""
                'See if the value is empty so that we can extract the value
                Select Case (secondQuote - 1) - (firstQuote + 1)
                    Case 0
                        'Has no value don't add
                    Case 1
                        'Has no value don't add
                    Case Else
                        val = str.Substring(firstQuote + 2, ((secondQuote - 2) - firstQuote - 1))
                End Select
                str = str.Remove(firstQuote - 6, secondQuote - (firstQuote - 7))
                str = str.Insert(firstQuote - 6, ".Contains(""" & val & """) ")
            Else
                'Handles '%value'
                'Did not find another % before the last quote, this is a EndsWith
                Dim val = str.Substring(firstQuote + 2, ((secondQuote - 2) - firstQuote - 1))
                str = str.Remove(firstQuote - 6, secondQuote - (firstQuote - 7))
                str = str.Insert(firstQuote - 6, ".EndsWith(""" & val & """) ")
            End If

        Else
            'Else the character after the first single quote is not a %, this is a StartWith or is Empty
            Dim secondQuote As Int32 = str.ToUpper.IndexOf("'", firstQuote + 1)
            If str.ToUpper.Chars(secondQuote - 1) = Chr(37) Then
                'Handles 'value%'
                'Found a % before the last quote, this is a StartsWith
                Dim val = str.Substring(firstQuote + 2, ((secondQuote - 2) - firstQuote - 1))
                str = str.Remove(firstQuote - 6, secondQuote - (firstQuote - 7))
                str = str.Insert(firstQuote - 6, ".StartsWith(""" & val & """) ")
            Else
                'Handles ''
                'Found no %
                str = str.Remove(firstQuote - 6, secondQuote - (firstQuote - 7))
                str = str.Insert(firstQuote - 6, ".Contains("""") ")
            End If
        End If
        rtn = replaceLike(str)
    Else
        Return str
    End If

    Return rtn
End Function

Answer 1

我发现Dynamic Linq Library中的predefinedTypes支持转换，我用它来制定以下内容：

"Convert.ToString(" & propertyName & ").Contains(""" & val & """)"

如果上面的propertyName是Nullable类型，则会导致将Nullable（Of）转换为字符串的问题。在Dynamic Linq Library中为ParseMemberAccess方法编辑Dynamic.vb代码允许转换工作。下面是对该方法中的Select Case语句所做的编辑：

            Select Case FindMethod(type, id, instance Is Nothing, args, mb)
                Case 0
                    Throw ParseError(errorPos, Res.NoApplicableMethod, id, GetTypeName(type))
                Case 1
                    Dim method = DirectCast(mb, MethodInfo)
                    If (Not IsPredefinedType(method.DeclaringType)) Then
                        Throw ParseError(errorPos, Res.MethodsAreInaccessible, GetTypeName(method.DeclaringType))
                    End If
                    If method.ReturnType.Equals(GetType(Void)) Then
                        Throw ParseError(errorPos, Res.MethodIsVoid, id, GetTypeName(method.DeclaringType))
                    End If
                    Dim newargs As Expression() = args
                    For Each a As Expression In args
                        If a.Type.IsGenericType AndAlso a.Type.GetGenericTypeDefinition = GetType(Nullable(Of )) Then
                            newargs(Array.IndexOf(args, a)) = System.Linq.Expressions.Expression.Convert(a, GetType(Object))
                        Else
                            newargs(Array.IndexOf(args, a)) = a
                        End If
                    Next
                    Return Expression.Call(instance, DirectCast(method, MethodInfo), newargs)
                Case Else
                    Throw ParseError(errorPos, Res.AmbiguousMethodInvocation, id, GetTypeName(type))
            End Select

动态Linq使用数据对象。如何将Int32转换为String以调用String.Contains（）

1 个答案: