sql - LINQ to SQL 错误 : specified cast is not valid

Question

您好，我正在尝试学习 LINQ，在 LINQ to SQL 中我遇到以下异常: 这是来自 Manning 出版物的 Linq In Action 的示例代码。 怎么了？

        DataContext db = new DataContext("E:\\Mahesh\\TempFolder\\DB\\NORTHWND.MDF");

        var contacts =
            from contact in db.GetTable<Contact>()
            where contact.City == "Paris"
            select contact;

        foreach (Contact aContact in contacts)
            Console.WriteLine("Bonjour " + aContact.Name);
        Console.Read();
    }
}

[Table(Name = "Customers")]
class Contact
{
    [Column(IsPrimaryKey = true)]
    public int CustomerID { get; set; }
    [Column(Name = "ContactName")]
    public string Name { get; set; }
    [Column]
    public string City { get; set; }
}

异常详细信息:

System.InvalidCastException was unhandled
HResult=-2147467262
Message=Specified cast is not valid.
Source=System.Data
StackTrace:
   at System.Data.SqlClient.SqlBuffer.get_Int32()
   at Read_Contact(ObjectMaterializer`1 )
   at System.Data.Linq.SqlClient.ObjectReaderCompiler.ObjectReader`2.MoveNext()
   at LinqDemo.Program.Main(String[] args) in c:\Users\MAHESH\Desktop\TechNode\C#\MyTechDos\LinqDemo\LinqDemo\Program.cs:line 51
   at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
   at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ThreadHelper.ThreadStart()
InnerException: 

Answer 1

如果我没记错的话，Northwind 中的 Customers 表没有将 CustomerID 作为 int(我认为是 NVARCHAR)。如果您手动编写 Contact 类，而不是让 LINQ to SQL 生成它，请确保类上的类型与数据库表中的类型匹配

编辑:从此链接http://msdn.microsoft.com/en-us/library/bb399575(v=vs.90).aspx我倾向于认为 CustomerID 字段不是 INT 而是 NVARCHAR(或 NCHAR)