[ad_1]
I'm using some free source code to create an e-commerce site in WebForms. It is the Visual Basic version of Getting Started with ASP.NET 4.5 Web Forms and Visual Studio 2013. I have been successful until I coded the ProductDetails.aspx.vb page. I replaced my object names and properties accordingly, but when I run the project, I get this error: Unable to cast object of type 'WhereEnumerableIterator`1[LethalLibrary.Book]' to type 'System.Linq.IQueryable`1[LethalLibrary.Book]'. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.InvalidCastException: Unable to cast object of type 'WhereEnumerableIterator`1[LethalLibrary.Book]' to type 'System.Linq.IQueryable`1[LethalLibrary.Book]'. Does Linq from VS2017 differ from VS2013? How do I fix this?
मैंने क्या प्रयास किया है:
वी.बी
Public Function GetBook(<QueryString("BookID")> BookId As Nullable(Of Integer)) As IQueryable(Of Book) Dim db = New BookContext() Dim query As IQueryable(Of Book) = db.Books If BookId.HasValue AndAlso BookId > 0 Then query = query.Where(CType(Function(p) p.BookID = BookId, Func(Of Book, Boolean))) ElseIf Not String.IsNullOrEmpty(BookTitle) Then query = query.Where(Function(p) String.Compare(p.BookTitle, BookTitle) = 0) Else query = Nothing End If Return query End Function
मैंने भी जोड़ा है
वी.बी
.Select(Function(p) p)
मेरे .where कथन के अंत तक, लेकिन वह भी काम नहीं आया।
वी.बी
<pre>Public Function GetBook(<QueryString("BookID")> BookId As Nullable(Of Integer)) As IQueryable(Of Book) Dim db = New BookContext() Dim query As IQueryable(Of Book) = db.Books If BookId.HasValue AndAlso BookId > 0 Then query = query.Where(CType(Function(p) p.BookID = BookId, Func(Of Book, Boolean))).Select(Function(p) p) Else query = Nothing End If Return query End Function
समाधान 1
प्रयोग का प्रयास करें Enumerable.Cast(TResult) विधि (IEnumerable) (System.Linq)[^] :
वीबी.नेट
Dim query As IQueryable(Of Book) = db.Books.Cast(Of Book)() _ .Where(Function(x) x.BookID = BookId) _ .ToList()
या Enumerable.OfType(TResult) विधि (IEnumerable) (System.Linq)[^]:
वीबी.नेट
Dim query As IQueryable(Of Book) = db.Books.OfType(Of Book)() _ .Where(Function(x) x.BookID = BookId) _ .ToList()
अधिक जानकारी के लिए कृपया देखें: समर्थित और असमर्थित LINQ तरीके (LINQ से इकाइयों तक) | माइक्रोसॉफ्ट डॉक्स[^]
समाधान 2
मुझे ASP.NET मंचों पर एक समाधान मिला; मैंने जोड़ा AsQueryable()
मेरे अंत तक query
परिवर्तनशील और यह काम कर गया!
वी.बी
Public Function GetBook(BookId As Nullable(Of Integer)) As IQueryable(Of Book) Dim BookTitle As String = "aaaa" Dim db = New ApplicationDbContext() Dim query As IQueryable(Of Book) = db.Books If BookId.HasValue AndAlso BookId > 0 Then query = (query.Where(CType(Function(p) p.BookId = BookId, Func(Of Book, Boolean)))).AsQueryable() ElseIf Not String.IsNullOrEmpty(BookTitle) Then query = (query.Where(Function(p) String.Compare(p.BookTitle, BookTitle) = 0)).AsQueryable() Else query = Nothing End If Return query End Function
समाधान 3
AsQueryable ने मेरे लिए भी काम किया (हालांकि cSharp में)
धन्यवाद
[ad_2]
コメント