阅读器关闭时尝试读取无效 - 但不关闭阅读器？

Question

在我的C＃应用​​程序中，我正在与SQL Compact数据库进行交互。在这方面，我有三张桌子; customer，list和customerlist（客户和列表是多对多的关系）。

我有一个函数，当我想要删除一个列表时调用。该功能也会删除customerlist表中的相关条目，只是为了清洁（因为如果列表本身已被删除，它们将不复存在）。

我的代码是这样的：

private void clearRedundantSubscriptions() 
    { 
     string sql; 
     // Check if there are any entries in customerlist table which point to non-existing lists 
     try 
     { 
      sql = "select distinct cl.listid from customerlist cl inner join list l on cl.listid != l.listid"; 
      SqlCeCommand cmdGetDisusedLists = new SqlCeCommand(sql, DbConnection.ceConnection); 
      SqlCeDataReader reader = cmdGetDisusedLists.ExecuteReader(); 
      while (reader.Read()) 
      { 
       DbFunctions.DeleteList(reader.GetInt32(0), false, false); 
      } 
     } 
     catch (Exception ex) 
     { 
      MessageBox.Show("Error cleaning up list entries." + ex.Message); 
     } 
     return; 
    } 

    public static bool DeleteList(int id, bool display, bool close) 
    { 
     string sql; 
     string title = ""; 
     bool ranOk = false; 
     try 
     { 
      sql = "select ShortDesc from list where listid=" + id; 
      DbFunctions.runSQL(sql, out title); 
      sql = "delete from list where ListId=" + id; 
      SqlCeCommand cmdDelList = new SqlCeCommand(sql, DbConnection.ceConnection); 
      cmdDelList.ExecuteNonQuery(); 
      sql = "delete from customerlist where listid=" + id; 
      SqlCeCommand cmdDelEntries = new SqlCeCommand(sql, DbConnection.ceConnection); 
      cmdDelEntries.ExecuteNonQuery(); 
      if (display) 
       General.doneWork(title + " list deleted."); 
      ranOk = true; 
     } 
     catch (Exception ex) 
     { 
      if (display) 
       MessageBox.Show("Unable to delete list. " + ex.Message); 
     } 
     finally 
     { 
      if (close) 
       DbConnection.closeConnection(); 
     } 
     return ranOk; 
    } 

    public static void closeConnection() 
    { 
     if (_sqlCeConnection != null) 
      _sqlCeConnection.Close(); 
    } 

你会在我deletelist功能注意到，我通过一个名为“关闭”一个布尔参数。我添加了这个，因为在阅读器内关闭与数据库的连接导致了上述错误。所以，现在，如果我想在阅读器中使用这个函数，我调用deleteList函数并确保'close'参数被传入为false。这不是问题 - 这意味着DbConnection.closeConnection是不是在此函数中调用。

所以我没有关闭阅读器，也没有数据库连接。那么，为什么我仍然得到这个错误的任何想法？

Answer 1

我修改了你的代码，试试看。

我不知道DbFunctions.runSQL方法中发生了什么，所以您可能需要在该调用之前重新打开连接。

private void clearRedundantSubscriptions() 
{ 
    string sql; 
    // Check if there are any entries in customerlist table which point to non-existing lists 
    var list = new List<int>(); 
    try 
    { 
     if (DbConnection.ceConnection.State == ConnectionState.Closed) 
      DbConnection.ceConnection.Open(); 

     sql = "select distinct cl.listid from customerlist cl inner join list l on cl.listid != l.listid"; 

     SqlCeCommand cmdGetDisusedLists = new SqlCeCommand(sql, DbConnection.ceConnection); 
     SqlCeDataReader reader = cmdGetDisusedLists.ExecuteReader(); 
     while (reader.Read()) 
     { 
      list.Add(reader.GetInt32(0)); 
     } 
    } 
    catch (Exception ex) 
    { 
     MessageBox.Show("Error cleaning up list entries." + ex.Message); 
     throw; 
    } 
    finally 
    { 
     DbConnection.closeConnection(); 
    } 

    foreach(var id in list) 
    { 
     DeleteList(id,false); 

    } 
    return; 
} 

public static bool DeleteList(int id, bool display) 
{ 
    string sql; 
    string title = ""; 
    bool ranOk = false; 
    try 
    { 
     sql = "select ShortDesc from list where listid=" + id; 
     DbFunctions.runSQL(sql, out title); 


     sql = "delete from list where ListId=" + id; 
     SqlCeCommand cmdDelList = new SqlCeCommand(sql, DbConnection.ceConnection); 
     cmdDelList.ExecuteNonQuery(); 
     sql = "delete from customerlist where listid=" + id; 
     SqlCeCommand cmdDelEntries = new SqlCeCommand(sql, DbConnection.ceConnection); 
     cmdDelEntries.ExecuteNonQuery(); 
     if (display) 
      General.doneWork(title + " list deleted."); 
     ranOk = true; 
    } 
    catch (Exception ex) 
    { 
     if (display) 
      MessageBox.Show("Unable to delete list. " + ex.Message); 
    } 
    finally 
    { 
      DbConnection.closeConnection(); 
    } 
    return ranOk; 
} 

public static void closeConnection() 
{ 
    if (_sqlCeConnection != null) 
     _sqlCeConnection.Close(); 
}