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());
                }
            }

        }

我使用此代码过滤数据库，并且在第一次运行它时收到该错误，第二次运行时我会收到该错误

System.InvalidOperationException：'已经存在与此Command关联的打开的DataReader，必须先关闭它。'

在此行中SqlDataReader dr = command2.ExecuteReader（）;

Answer 1

使用后，您需要关闭数据读取。

这是您不使用Using()时的代码外观

通过评论了解

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();
            }

        }

Answer 2

您必须处置适配器创建的第一个数据读取器。 using语句将负责处理开箱即用的资源。

您只能将数据读取器与一个命令关联使用（就像错误状态一样）。创建2个using语句并准备2个数据读取器。这可以与using（connection）相同，因为一个连接可以用于多个命令，但是每个命令必须具有单独的数据读取器。

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

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

了解有关HERE的更多信息

我第二次使用它时出现DataReader错误

2 个答案: