Question

我正在尝试列出我的SQLite数据库中的所有表，但我只需要普通的表而不是系统表。我尝试使用foreach并在循环时删除行，但我得到一个例外。任何人都可以请指出我在这里做错了什么，因为我真的没有看到我出错的地方。

我唯一想到的是我在循环时无法从DataTable中删除，但我不知道如何处理这个问题。

数据库目前包含4个表，3个普通表和1个系统表

代码：

        SQLiteConnection connection = new SQLiteConnection("Data Source=db.sqlite");

        connection.Open();

        DbTables = connection.GetSchema("Tables");

        foreach (DataRow row in DbTables.Rows)
        {
            Console.WriteLine(row[3].ToString());

            if (row[3].ToString() == "SYSTEM_TABLE")
                DbTables.Rows.Remove(row);
        }

        connection.Close();

例外：

System.Windows.Data Error: 17 : Cannot get 'Main' value (type 'MainViewModel') from '' (type 'ViewModelLocator'). BindingExpression:Path=Main; DataItem='ViewModelLocator' (HashCode=65325907); target element is 'MainWindow' (Name=''); target property is 'DataContext' (type 'Object') TargetInvocationException:'System.Reflection.TargetInvocationException: Property accessor 'Main' on object 'DatabaseExplorer.ViewModel.ViewModelLocator' threw the following exception:'Exception has been thrown by the target of an invocation.' ---> System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.InvalidOperationException: Collection was modified; enumeration operation might not execute.
   at System.Data.RBTree`1.RBTreeEnumerator.MoveNext()
   at DatabaseExplorer.ViewModel.MainViewModel..ctor(IDataService dataService) in Project\ViewModel\MainViewModel.cs:line 61
   --- End of inner exception stack trace ---
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
   at System.Reflection.RuntimeConstructorInfo.Invoke(BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at System.Reflection.ConstructorInfo.Invoke(Object[] parameters)
   at GalaSoft.MvvmLight.Ioc.SimpleIoc.MakeInstance[TClass]()
   --- End of inner exception stack trace ---
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
   at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
   at System.Delegate.DynamicInvokeImpl(Object[] args)
   at System.Delegate.DynamicInvoke(Object[] args)
   at GalaSoft.MvvmLight.Ioc.SimpleIoc.DoGetService(Type serviceType, String key)
   at GalaSoft.MvvmLight.Ioc.SimpleIoc.GetInstance[TService]()
   at DatabaseExplorer.ViewModel.ViewModelLocator.get_Main() in Project\ViewModel\ViewModelLocator.cs:line 54
   --- End of inner exception stack trace ---
   at System.ComponentModel.ReflectPropertyDescriptor.GetValue(Object component)
   at MS.Internal.Data.ValueTable.GetValue(Object item, PropertyDescriptor pd, Boolean indexerIsNext)
   at MS.Internal.Data.PropertyPathWorker.GetValue(Object item, Int32 level)
   at MS.Internal.Data.PropertyPathWorker.RawValue(Int32 k)'

删除if子句时的控制台输出：

SYSTEM_TABLE
table
table
table

提前致谢！

Answer 1

枚举时无法修改集合。因此，您可以将foreach循环更改为for，也可以创建将要删除的行的临时集合，然后将其删除。

第一种方法（需要测试，我现在不在我的电脑前）：

for (int i = DbTables.Rows.Count; i >=0 ; i--)
{
    if (DbTables.Rows[i].ToString() == "SYSTEM_TABLE")
         DbTables.Rows.RemoveAt(i);
}

第二种方法：

DbTables = connection.GetSchema("Tables");

var rowsToBeRemoved = new List<DataRow>();

foreach (DataRow row in DbTables.Rows)
{
    Console.WriteLine(row[3].ToString());

    if (row[3].ToString() == "SYSTEM_TABLE")
       rowsToBeRemoved.Add(row);
}

foreach DataRow row in rowsToBeRemoved)
{
    DbTables.Rows.Remove(row);
}

无法从DataTable中删除DataRow

1 个答案: