c# - 如何为类集属性传递参数(不是类声明)

Question

背景:

我正在制作一个 c# 4.0 类以供重用，因此我可以将一个参数发送到我程序的大多数方法并传递一个“连接”对象，该对象可以包含以下内容:

• 连接字符串
• DbConnection(即 OleDbConnection 或 SQLConnection)
• DataReader(即 OleDbDataReader 或 SQLDataReader)

理由是我最终会升级到 SQL Server 并且不想更改我的方法参数或代码太多。方法通常必须从同一个数据库中到处调用快速查询。

问题:

如何在以下行的方法中正确设置(和调用)DbType 的 DRMDbConnection“设置”参数(现在硬编码为整数 1)的右侧:

set { drmDbConnection = SetDRMDbConnection(1); }

示例代码:

public class Connections
{

public string DRMDbConnectionString { get; set; }
private object drmDbConnection;

public object DRMDbConnection
{
  get { return drmDbConnection; }
  set { drmDbConnection = SetDRMDbConnection(1); }
}

private object SetDRMDbConnection(int DbType)
{
  if (DbType == 1)
    return new System.Data.OleDb.OleDbConnection();
  else
    return new SqlConnection();
}

10 月 31 日编辑

我更新了类代码以使用推荐的 IDbConnection、IDbCommand 和 IDataReader。注意:如果不更改 SQL Server 连接字符串，您将收到错误消息:“已经有一个打开的 DataReader 与此命令关联，必须先将其关闭。”因此将其添加到连接字符串:“MultipleActiveResultSets=True；”

更新类代码

public class Connections
// reusuable object to hold all database Connections and a convenient DataReader and Command object.
// Its purpose is to also be able to handle your choice of database connection, i.e. OleDb or SQL Server.
{
public string DRMConnectionString { get; set; }
public IDbConnection DRMConnection;

public IDbCommand DRMCommand
{
  get { return DRMConnection.CreateCommand(); }
  set { }
}

public int DRMConnectionType
// must be called to setup database connection and command.  The connectionstring must be previously set.
{
  set
  {
    if (value == 1)
      DRMConnection = new System.Data.OleDb.OleDbConnection(DRMConnectionString);
    else
      DRMConnection = new SqlConnection(DRMConnectionString);
  }
}

public void CloseConnections()
{
  if (DRMCommand != null)
    DRMCommand.Dispose();

  if ((DRMConnection != null) && (DRMConnection.State != ConnectionState.Closed))
    DRMConnection.Close();
}
}

调用代码

var conn = new Connections();
conn.DRMConnectionString = "my connection string";
conn.DRMConnectionType = 2;
conn.DRMConnection.Open();
try
{
  using (var cmd = conn.DRMCommand)
  {
    cmd.CommandText = "SELECT * FROM MyTable";
    using (var rdr = cmd.ExecuteReader())
    {
      while (rdr.Read())      
      {
         CallSubMethodThatAlsoOpensDataReader(conn);  
      } 
    } 
  }
}
finally
{
  conn.CloseConnections();
} 


CallSubMethodThatAlsoOpensDataReader(Connections Conn)
{
  using (var cmd = Conn.DRMCommand)
  {
    cmd.CommandText = "SELECT * FROM MyOtherTable";
    using (var rdr = cmd.ExecuteReader())  // Error: There is already an open DataReader associated with this Command which must be closed first.
    {
       ; // do stuff
    } 
  }
}

Answer 1

您可以按如下方式使其工作:

public IDbConnection DRMDbConnection // Note the change of the type
{
    get { return drmDbConnection; }
}
public int DrmDbConnectionType
{
    set {
        if (vale== 1)
            drmDbConnection = new System.Data.OleDb.OleDbConnection();
        else
            drmDbConnection = new SqlConnection();
    }
}

The reasoning is that I will eventually upgrade to SQL Server and don’t want to change my method parameters or code so much.

我认为这是您要解决的关键问题。与其针对特定类编程，不如针对接口(interface)编程。具体来说，使用 IDbConnection代替 SqlConnection 或 OleDbConnection 比将其封装在 DRMDbConnection 中更能让您隐藏确切的类型。