Question

我想从NHibernate的SqlClientBatchingBatcher类中继承这样的代码（代码取自TooManyRowsAffectedException with encrypted triggers）：

public class NonBatchingBatcherWithoutVerification : SqlClientBatchingBatcher
{
    public NonBatchingBatcherWithoutVerification(ConnectionManager connectionManager, IInterceptor interceptor) : base(connectionManager, interceptor)
    {}

    protected override void DoExecuteBatch(IDbCommand ps)
    {
        log.DebugFormat("Executing batch");
        CheckReaders();
        Prepare(currentBatch.BatchCommand);
        if (Factory.Settings.SqlStatementLogger.IsDebugEnabled)
        {
            Factory.Settings.SqlStatementLogger.LogBatchCommand(currentBatchCommandsLog.ToString());
            currentBatchCommandsLog = new StringBuilder().AppendLine("Batch commands:");
        }

        int rowsAffected = currentBatch.ExecuteNonQuery();

        // Removed the following line
        //Expectations.VerifyOutcomeBatched(totalExpectedRowsAffected, rowsAffected);

        currentBatch.Dispose();
        totalExpectedRowsAffected = 0;
        currentBatch = new SqlClientSqlCommandSet();
    }
}

请注意此处方法中访问的一些成员（如currentBatch或totalExpectedRowsAffected）。

嗯，事实证明这些成员在当前NHibernate 3.3源代码的超类中实际上是私有的。那么如何在不复制整个事物的情况下有效地继承类呢？这是类中未经修改的NHibernate代码：

 public class SqlClientBatchingBatcher : AbstractBatcher
{
    private int _batchSize;
    private int _totalExpectedRowsAffected;
    private SqlClientSqlCommandSet _currentBatch;
    private StringBuilder _currentBatchCommandsLog;
    private readonly int _defaultTimeout;

    public SqlClientBatchingBatcher(ConnectionManager connectionManager, IInterceptor interceptor)
        : base(connectionManager, interceptor)
    {
        _batchSize = Factory.Settings.AdoBatchSize;
        _defaultTimeout = PropertiesHelper.GetInt32(Cfg.Environment.CommandTimeout, Cfg.Environment.Properties, -1);

        _currentBatch = CreateConfiguredBatch();
        //we always create this, because we need to deal with a scenario in which
        //the user change the logging configuration at runtime. Trying to put this
        //behind an if(log.IsDebugEnabled) will cause a null reference exception 
        //at that point.
        _currentBatchCommandsLog = new StringBuilder().AppendLine("Batch commands:");
    }

    public override int BatchSize
    {
        get { return _batchSize; }
        set { _batchSize = value; }
    }

    protected override int CountOfStatementsInCurrentBatch
    {
        get { return _currentBatch.CountOfCommands; }
    }

    public override void AddToBatch(IExpectation expectation)
    {
        _totalExpectedRowsAffected += expectation.ExpectedRowCount;
        IDbCommand batchUpdate = CurrentCommand;
        Driver.AdjustCommand(batchUpdate);
        string lineWithParameters = null;
        var sqlStatementLogger = Factory.Settings.SqlStatementLogger;
        if (sqlStatementLogger.IsDebugEnabled || Log.IsDebugEnabled)
        {
            lineWithParameters = sqlStatementLogger.GetCommandLineWithParameters(batchUpdate);
            var formatStyle = sqlStatementLogger.DetermineActualStyle(FormatStyle.Basic);
            lineWithParameters = formatStyle.Formatter.Format(lineWithParameters);
            _currentBatchCommandsLog.Append("command ")
                .Append(_currentBatch.CountOfCommands)
                .Append(":")
                .AppendLine(lineWithParameters);
        }
        if (Log.IsDebugEnabled)
        {
            Log.Debug("Adding to batch:" + lineWithParameters);
        }
        _currentBatch.Append((System.Data.SqlClient.SqlCommand) batchUpdate);

        if (_currentBatch.CountOfCommands >= _batchSize)
        {
            ExecuteBatchWithTiming(batchUpdate);
        }
    }

    protected override void DoExecuteBatch(IDbCommand ps)
    {
        Log.DebugFormat("Executing batch");
        CheckReaders();
        Prepare(_currentBatch.BatchCommand);
        if (Factory.Settings.SqlStatementLogger.IsDebugEnabled)
        {
            Factory.Settings.SqlStatementLogger.LogBatchCommand(_currentBatchCommandsLog.ToString());
            _currentBatchCommandsLog = new StringBuilder().AppendLine("Batch commands:");
        }

        int rowsAffected;
        try
        {
            rowsAffected = _currentBatch.ExecuteNonQuery();
        }
        catch (DbException e)
        {
            throw ADOExceptionHelper.Convert(Factory.SQLExceptionConverter, e, "could not execute batch command.");
        }

        Expectations.VerifyOutcomeBatched(_totalExpectedRowsAffected, rowsAffected);

        _currentBatch.Dispose();
        _totalExpectedRowsAffected = 0;
        _currentBatch = CreateConfiguredBatch();
    }

    private SqlClientSqlCommandSet CreateConfiguredBatch()
    {
        var result = new SqlClientSqlCommandSet();
        if (_defaultTimeout > 0)
        {
            try
            {
                result.CommandTimeout = _defaultTimeout;
            }
            catch (Exception e)
            {
                if (Log.IsWarnEnabled)
                {
                    Log.Warn(e.ToString());
                }
            }
        }

        return result;
    }
}

我忽视了什么吗？似乎是一种相当糟糕的方法来复制整个事情只是为了覆盖对任何私有成员的所有访问权限。我只想覆盖一种方法！

Answer 1

合法访问基类的私有成员只有一种方法：将派生类放在基类中：

class Base
{
    private int x;
    private class Derived : Base
    {
        private void M()
        {
            Console.WriteLine(this.x); // legal!
        }
    }
}

当然，如果你可以将类放在基类中，那么你也可以重写基类，以便成员受到保护。

原作者让这些成员变得私密，这暗示了这个课程并不是为你设计的。

Answer 2

如果将它们设置为私有，那么你可以做的就是没有（没有使用反射，这是丑陋的，当然也不总是安全的）。

Answer 3

无法访问

Private个超类成员，因为它们是private。 OOP中的封装是禁止此直接访问，因此确保对象正常运行。
可能有properties访问私有成员，这些是您可以用来读取/写入私有成员的成员。这些属性将确保不会对对象造成任何伤害。

Answer 4

您可以使用反射访问父类的私有字段，属性和方法（例如，访问此处所述的字段：Reflecting a private field from a base class）

这不安全，但是私有的想法是库实现可能会改变，那些私有方法，字段和属性可能会改变或消失。如果他们更改了实现，更新可能会破坏您的代码。

那就是说，我自己做了几次。你只需要权衡风险。

如何在覆盖中访问超类的私有成员？

4 个答案: