System.Data.SQLite类型关联int字符串列

Question

从我对SQLite的了解来看，它有一个叫做类型关联的功能，这意味着数据类型不是严格强制的(更多信息在这里)。

我正在从使用EF4.1的POCO对象在另一个应用程序中创建的数据库中读取，问题出现时，假设字符串字段中有一个整数。我可以理解，如果int字段中有一个非数字字符串，就会抛出异常……但为什么这会毁了我的应用?

这是我的测试代码的一个样本，我已经删除了所有其他的东西，直到我只剩下最少的代码，使这个弹出。

Public Class TVSerie
    Public Property Id As Integer
    Public Property PrettyName As String
End Class
Public Class TVSeriesDb
    Inherits DbContext
    Public Property TVSeries As DbSet(Of TVSerie)
End Class
Public Class HomeController
    Inherits System.Web.Mvc.Controller
    Function Index() As ActionResult
        Dim db As New TVSeriesDb
        Dim sb As New StringBuilder
        Dim series = db.TVSeries.Where(Function(c) c.PrettyName.Length > 0)
        For Each s In series
            sb.Append(s.Id & "-" & s.PrettyName & "<br/>")
        Next
        Return Content(sb.ToString)
    End Function
End Class

错误弹出在"PrettyName"列与TVSeries 24:

[InvalidCastException: Specified cast is not valid.]
System.Data.SQLite.SQLiteDataReader.VerifyType(Int32 i, DbType typ) +492
System.Data.SQLite.SQLiteDataReader.GetString(Int32 i) +131
[TargetInvocationException: Exception has been thrown by the target of an invocation.]
   System.RuntimeMethodHandle._InvokeMethodFast(IRuntimeMethodInfo method, Object target,   Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeType typeOwner) +0
   System.RuntimeMethodHandle.InvokeMethodFast(IRuntimeMethodInfo method, Object target, Object[] arguments, Signature sig, MethodAttributes methodAttributes, RuntimeType typeOwner) +72
   System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks) +251
   System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture) +28
   System.Data.Common.Internal.Materialization.ErrorHandlingValueReader`1.GetValue(DbDataReader reader, Int32 ordinal) +342
   System.Data.Common.Internal.Materialization.Shaper.GetPropertyValueWithErrorHandling(Int32 ordinal, String propertyName, String typeName) +79
   lambda_method(Closure , Shaper ) +167
   System.Data.Common.Internal.Materialization.Shaper.HandleEntityAppendOnly(Func`2 constructEntityDelegate, EntityKey entityKey, EntitySet entitySet) +218
   lambda_method(Closure , Shaper ) +291
   System.Data.Common.Internal.Materialization.Coordinator`1.ReadNextElement(Shaper shaper) +170
   System.Data.Common.Internal.Materialization.SimpleEnumerator.MoveNext() +84
   Test.Controllers.HomeController.Index() in C:ProjectsPlayListShufflerTestControllersHomeController.vb:14
   lambda_method(Closure , ControllerBase , Object[] ) +96
   System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object[] parameters) +17
   System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary`2 parameters) +208
   System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters) +27
   System.Web.Mvc.<>c__DisplayClass15.<InvokeActionMethodWithFilters>b__12() +55
   System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func`1 continuation) +263
   System.Web.Mvc.<>c__DisplayClass17.<InvokeActionMethodWithFilters>b__14() +19
   System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodWithFilters(ControllerContext controllerContext, IList`1 filters, ActionDescriptor actionDescriptor, IDictionary`2 parameters) +191
   System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName) +343
   System.Web.Mvc.Controller.ExecuteCore() +116
   System.Web.Mvc.ControllerBase.Execute(RequestContext requestContext) +97
   System.Web.Mvc.ControllerBase.System.Web.Mvc.IController.Execute(RequestContext requestContext) +10
   System.Web.Mvc.<>c__DisplayClassb.<BeginProcessRequest>b__5() +37
   System.Web.Mvc.Async.<>c__DisplayClass1.<MakeVoidDelegate>b__0() +21
   System.Web.Mvc.Async.<>c__DisplayClass8`1.<BeginSynchronous>b__7(IAsyncResult _) +12
   System.Web.Mvc.Async.WrappedAsyncResult`1.End() +62
   System.Web.Mvc.<>c__DisplayClasse.<EndProcessRequest>b__d() +50
   System.Web.Mvc.SecurityUtil.<GetCallInAppTrustThunk>b__0(Action f) +7
   System.Web.Mvc.SecurityUtil.ProcessInApplicationTrust(Action action) +22
   System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +60
   System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result) +9
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +8920029
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +184

Answer 1

虽然sqlite不是强类型的(这与像Python这样的动态类型语言很好地配合)，但。net的强类型特性是在包装器中强制执行的。因此，当读取表时检测到的列类型是Reader.Getxxx(n)所需的类型。