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SqlCommand.Clone() 是否创建深复制或浅复制？

发布于 2024-11-26 07:43:21 字数 103 浏览 1 评论 0原文

SqlCommand.Clone() 是否创建深复制或浅复制？另外，从多个线程并发调用 Clone() 是否安全（创建一个多个线程可以复制、设置参数值并执行的命令）？

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扮仙女 2024-12-03 07:43:21

从多个线程调用 Clone 并不安全，因为 SqlCommand 类本身不是线程安全类。在克隆之前你应该lock。

但是你可以使用Reflector等程序查看SqlCommand.Clone()方法，这里是实际的代码：

public SqlCommand Clone()
{
    SqlCommand command = new SqlCommand(this);
    Bid.Trace("<sc.SqlCommand.Clone|API> %d#, clone=%d#\n", this.ObjectID, command.ObjectID);
    return command;
}

internal static void Trace(string fmtPrintfW, int a1, int a2)
{
    if (((modFlags & ApiGroup.Trace) != ApiGroup.Off) && (modID != NoData))
    {
        NativeMethods.Trace(modID, UIntPtr.Zero, UIntPtr.Zero, fmtPrintfW, a1, a2);
    }
}

[DllImport("System.Data.dll", EntryPoint="DllBidTraceCW", CallingConvention=CallingConvention.Cdecl, CharSet=CharSet.Unicode)]
internal static extern void Trace(IntPtr hID, UIntPtr src, UIntPtr info, string fmtPrintfW, int a1, int a2);

private SqlCommand(SqlCommand from) : this()
{
    this.CommandText = from.CommandText;
    this.CommandTimeout = from.CommandTimeout;
    this.CommandType = from.CommandType;
    this.Connection = from.Connection;
    this.DesignTimeVisible = from.DesignTimeVisible;
    this.Transaction = from.Transaction;
    this.UpdatedRowSource = from.UpdatedRowSource;
    SqlParameterCollection parameters = this.Parameters;
    foreach (object obj2 in from.Parameters)
    {
        parameters.Add((obj2 is ICloneable) ? (obj2 as ICloneable).Clone() : obj2);
    }
}

您可以看到它创建了一个新实例并向其中添加了旧实例的所有属性，但它不会深度复制所有属性“例如 Connection”，因此它是浅复制。

It is not safe to call Clone from multiple threads because the SqlCommand class itself is not a thread safe class. you should lock before cloning..

However you can look at the SqlCommand.Clone() method using programs like Reflector, here is the actual code:

public SqlCommand Clone()
{
    SqlCommand command = new SqlCommand(this);
    Bid.Trace("<sc.SqlCommand.Clone|API> %d#, clone=%d#\n", this.ObjectID, command.ObjectID);
    return command;
}

internal static void Trace(string fmtPrintfW, int a1, int a2)
{
    if (((modFlags & ApiGroup.Trace) != ApiGroup.Off) && (modID != NoData))
    {
        NativeMethods.Trace(modID, UIntPtr.Zero, UIntPtr.Zero, fmtPrintfW, a1, a2);
    }
}

[DllImport("System.Data.dll", EntryPoint="DllBidTraceCW", CallingConvention=CallingConvention.Cdecl, CharSet=CharSet.Unicode)]
internal static extern void Trace(IntPtr hID, UIntPtr src, UIntPtr info, string fmtPrintfW, int a1, int a2);

private SqlCommand(SqlCommand from) : this()
{
    this.CommandText = from.CommandText;
    this.CommandTimeout = from.CommandTimeout;
    this.CommandType = from.CommandType;
    this.Connection = from.Connection;
    this.DesignTimeVisible = from.DesignTimeVisible;
    this.Transaction = from.Transaction;
    this.UpdatedRowSource = from.UpdatedRowSource;
    SqlParameterCollection parameters = this.Parameters;
    foreach (object obj2 in from.Parameters)
    {
        parameters.Add((obj2 is ICloneable) ? (obj2 as ICloneable).Clone() : obj2);
    }
}

You can see that it create a new instance and add to it all properties of the old one, but it does not deep copy all properties "like Connection for instance" and so it a shallow copy.

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