Question

I try to use DataAdapter in C#.net. and still I do not understand something about DataAdapter.

我阅读了许多关于数据应用和数据检索的文章和博客。

我的理解是,数据Adapter将在必要时自动开放和关闭数据库。

But,

//conn.Open();
AdsDataAdapter da;
da = new AdsDataAdapter("Select * from Test", conn);
AdsCommandBuilder cb;
cb = new AdsCommandBuilder(da);

DataSet ds = new DataSet();
da.Fill(ds, "Test");

DataRow newrow = ds.Tables["Test"].NewRow();
newrow["Name"] = "How about";
ds.Tables["Test"].Rows.Add(newrow);
da.Update(ds, "Test");

当我操作上述法典时,我收到一个错误的信息,即“必须开放”

为什么适应者不能自动开放联系?

并且,我希望插入数据,以插入“共同点”(为这一试验,我打开了链接)。

da.InsertCommand = new AdsCommand("INSERT INTO test (NAME) values( Insert Test #1 )", conn);
//da.InsertCommand.ExecuteNonQuery(); // it works
da.Update(ds,"Test"); //but it does not works.

许多使用适应器的例子。更新,但对于我来说,它并不发挥作用:

No error and nothing inserted.

并且使用。插入Command.ExecuteNonQuery();相反,它正在更新。

what am I doing wrong?

感谢!

Answer 1

MSDN 。

The Fill method implicitly opens the Connection that the DataAdapter is using if it finds that the connection is not already open. If Fill opened the connection, it will also close the connection when Fill is finished. This can simplify your code when dealing with a single operation such as a Fill or an Update.

This means that after da.Fill(ds, "Test"); your connection is closed by the method itself. But you need it open for the following Update (and that fails)

EDIT:源自您的上述代码的假编码

using(AdsConnection com = new AdsConnection(connectionString));
{
    conn.Open();
    using(AdsDataAdapter da = new AdsDataAdapter("Select * from Test", conn))
    {
        AdsCommandBuilder cb = new AdsCommandBuilder(da); 
        DataSet ds = new DataSet(); 
        da.Fill(ds, "Test"); 

        // Now the connection is still open and you can issue other commands

       DataRow newrow = ds.Tables["Test"].NewRow(); 
       newrow["Name"] = "How about"; 
       ds.Tables["Test"].Rows.Add(newrow); 

       // da.Update should work here. No more connection closed.
       da.Update(ds, "Test"); 
    }
} // Exiting from the using block, the connection will be closed

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