DataReader not closed when Connection is closed, consequences?

问题

for example i have this code :

Sub Month()
    Dim Conn As New Data.OracleClient.OracleConnection
    Conn.Open()
    Try

        Dim Cmd As New Data.OracleClient.OracleCommand
        With Cmd
            .Connection = Conn
            .CommandType = Data.CommandType.Text
            .CommandText = "SELECT * FROM MONTH"
        End With
        Dim datareader As Data.OracleClient.OracleDataReader = Cmd.ExecuteReader
        While datareader.Read
            Response.Write(datareader(0))
        End While
    Catch ex As Exception
        Throw ex
    Finally
        Conn.Close()
    End Try
End Sub

What will happen to the datareader when the Connection is closed ( Conn.close)

Will the Cursor that is used by the datareader be freed ? or will it stay open ?

If the cursor that is used by the datareader is still open , when will it be automatically closed ? or should i just closed it manually ?

Will it cause the dreaded "ORA-01000: maximum open cursors exceeded" ?

thanks in advance

回答1:

CommandBehavior.CloseConnection

When you pass above values as argument to ExecuteReader 1. there is no need to close connection explicitly connection get close when you close your reader

check full post : http://pranayamr.blogspot.com/2010/11/executereader-with-commanbehavior.html

回答2:

You should create the objects in a using block so they are properly disposed:

Using Conn As New Data.SqlClient.SqlConnection
    Conn.Open()

    Dim Cmd As New Data.SqlClient.SqlCommand
    With Cmd
        .Connection = Conn
        .CommandType = Data.CommandType.Text
        .CommandText = "SELECT * FROM MONTH"
    End With

    Using datareader As Data.SqlClient.SqlDataReader = Cmd.ExecuteReader()
        While datareader.Read()
            Response.Write(datareader(0))
        End While
    End Using
End Using

There is no need to call Close on either the connection or the datareader.

回答3:

Just make new object of data reader after it been closed

private void button2_Click(object sender, EventArgs e)
    {
        //SqlConnection cn1 = new SqlConnection();
        cn.ConnectionString = "server = .\\SQLEXPRESS ; database=store ; integrated security = true  ";
        SqlCommand cm = new SqlCommand("select * from emp", cn);
        cn.Open();
        SqlDataReader dr = cm.ExecuteReader();
        DataTable dt = new DataTable();
        dt.Load(dr);
        dataGridView1.DataSource = dt.DefaultView ;
        //SqlCommand cm3 = new SqlCommand("select * from emp", cn1);
        SqlDataReader dr1 = cm.ExecuteReader();
        listBox1.Items.Clear();
        while (dr1.Read())
        {
            //listBox1.Items.Add(dr.GetString(2));
            listBox1.Items.Add(dr1["name"]);

        }
        cn.Close();
    }

回答4:

Why shouldn't you explicitly close the reader like this.

datareader.Close()

Dim Conn As New Data.SqlClient.SqlConnection
Conn.Open()
Try

    Dim Cmd As New Data.SqlClient.SqlCommand
    With Cmd
        .Connection = Conn
        .CommandType = Data.CommandType.Text
        .CommandText = "SELECT * FROM MONTH"
    End With
    Dim datareader As Data.SqlClient.SqlDataReader = Cmd.ExecuteReader
    While datareader.Read
        Response.Write(datareader(0))
    End While
    datareader.Close()
Catch ex As Exception
    Throw ex
Finally
    Conn.Close()
End Try

来源：https://stackoverflow.com/questions/6182884/datareader-not-closed-when-connection-is-closed-consequences

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