第二次使用 DataReader 错误

Question

var filterConditions = new[] {
       CreateSqlFilter("CIVILIDD", ID_No, selectCommand, false),


};

        string filterCondition = filterConditions.Any(a => a != null) ? filterConditions.Where(a => a != null).Aggregate((filter1, filter2) => String.Format("{0} AND {1}", filter1, filter2)) : (string)null;

        using (var connection = new SqlConnection(ConfigurationManager.ConnectionStrings["my"].ConnectionString))
        {
            selectCommand.Connection = connection;
            selectCommand.CommandText = filterCondition == null ? "SELECT * FROM _4" : "SELECT * FROM _4 WHERE " + filterCondition;
            connection.Open();
            SqlDataAdapter adapter = new SqlDataAdapter(selectCommand);
            DataTable dataSource = new DataTable();
            adapter.Fill(dataSource);
            dataGridView2.DataSource = dataSource;

            using (SqlCommand command2 = new SqlCommand("SELECT * FROM [_4] WHERE CIVILIDD = @id", mycon))
            {

                command2.Parameters.AddWithValue("@id", ID_No.Text);

                SqlDataReader dr = command2.ExecuteReader();





                while (dr.Read())
                {

                    txtname1.Text = (dr["name1"].ToString());
                    txtname2.Text = (dr["name2"].ToString());
                    Governorate.Text = (dr["Governorate"].ToString());
                    City.Text = (dr["City"].ToString());
                    Block.Text = (dr["Block"].ToString());
                    Street.Text = (dr["Street"].ToString());
                    Avenue.Text = (dr["Avenue"].ToString());
                    House.Text = (dr["House"].ToString());
                    Floor.Text = (dr["Floor"].ToString());
                    flat.Text = (dr["flat"].ToString());
                }
            }

        }

我使用这段代码来过滤我的数据库，当我第一次运行时我得到了那个错误，它在第二次工作时很好我得到了这个错误

System.InvalidOperationException: 'There is already an open DataReader associated with this Command which must be closed first.'

in this line SqlDataReader dr = command2.ExecuteReader();

Answer 1

您必须处理适配器创建的第一个数据reader。 using 语句将处理开箱即用的资源。

您只能将数据 reader 与一个命令相关联（就像错误状态一样）。创建2个using语句，准备2个datareaders。这可以在同一个 using( connection ) 中，因为一个连接可以用于多个命令，但是每个命令必须有单独的数据readers。

using (SqlDataAdapter a = new SqlDataAdapter("SELECT * FROM EmployeeIDs", c))
{
}

using( ..command2.. )
{
 SqlDataReader dr = command2.ExecuteReader();
}

在那里阅读更多信息 HERE

Answer 2

使用后需要关闭datareadre。

当您不使用 Using()

时，您的代码应该是这样的

看评论看懂

var filterConditions = new[] {
       CreateSqlFilter("CIVILIDD", ID_No, selectCommand, false),


};

        string filterCondition = filterConditions.Any(a => a != null) ? filterConditions.Where(a => a != null).Aggregate((filter1, filter2) => String.Format("{0} AND {1}", filter1, filter2)) : (string)null;

        using (var connection = new SqlConnection(ConfigurationManager.ConnectionStrings["my"].ConnectionString))
        {
            selectCommand.Connection = connection;
            selectCommand.CommandText = filterCondition == null ? "SELECT * FROM _4" : "SELECT * FROM _4 WHERE " + filterCondition;
            connection.Open();
            SqlDataAdapter adapter = new SqlDataAdapter(selectCommand);
            DataTable dataSource = new DataTable();
            adapter.Fill(dataSource);
            dataGridView2.DataSource = dataSource;

            using (SqlCommand command2 = new SqlCommand("SELECT * FROM [_4] WHERE CIVILIDD = @id", mycon))
            {

                command2.Parameters.AddWithValue("@id", ID_No.Text);

                SqlDataReader dr = command2.ExecuteReader();





                while (dr.Read())
                {

                    txtname1.Text = (dr["name1"].ToString());
                    txtname2.Text = (dr["name2"].ToString());
                    Governorate.Text = (dr["Governorate"].ToString());
                    City.Text = (dr["City"].ToString());
                    Block.Text = (dr["Block"].ToString());
                    Street.Text = (dr["Street"].ToString());
                    Avenue.Text = (dr["Avenue"].ToString());
                    House.Text = (dr["House"].ToString());
                    Floor.Text = (dr["Floor"].ToString());
                    flat.Text = (dr["flat"].ToString());
                }
                 // Close and Dispose the datareader
                 dr.Close();
                 dr.Dispose();
            }

        }

第二次使用 DataReader 错误

DataReader error when i us it in the second time

c#

datareader