閱讀器關閉時嘗試讀取無效 - 但不關閉閱讀器？

Question

在我的C＃應用​​程序中，我正在與SQL Compact數據庫進行交互。在這方面，我有三張桌子; customer，list和customerlist（客戶和列表是多對多的關係）。

我有一個函數，當我想要刪除一個列表時調用。該功能也會刪除customerlist表中的相關條目，只是爲了清潔（因爲如果列表本身已被刪除，它們將不復存在）。

我的代碼是這樣的：

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(); 
    } 

你會在我deletelist功能注意到，我通過一個名爲「關閉」一個布爾參數。我添加了這個，因爲在閱讀器內關閉與數據庫的連接導致了上述錯誤。所以，現在，如果我想在閱讀器中使用這個函數，我調用deleteList函數並確保'close'參數被傳入爲false。這不是問題 - 這意味着DbConnection.closeConnection是不是在此函數中調用。

所以我沒有關閉閱讀器，也沒有數據庫連接。那麼，爲什麼我仍然得到這個錯誤的任何想法？

Answer 1

我修改了你的代碼，試試看。

我不知道DbFunctions.runSQL方法中發生了什麼，所以您可能需要在該調用之前重新打開連接。

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(); 
}