在进行C#语言的3层项目时,我遇到了“尝试在关闭阅读器时调用Read无效”的错误。 我的目标是通过将两个表连接在一起检索地址数据列,并在下拉列表中显示。 以下是我的数据访问层:
public List<Distribution> getDistributionAll()
{
List<Distribution> distributionAll = new List<Distribution>();
string address;
SqlDataReader dr = FoodBankDB.executeReader("SELECT b.addressLineOne FROM dbo.Beneficiaries b INNER JOIN dbo.Distributions d ON d.beneficiary = b.id");
while (dr.Read())
{
address = dr["addressLineOne"].ToString();
distributionAll.Add(new Distribution(address));
}
return distributionAll;
}
这是我的FoodBankDB类:
public class FoodBankDB
{
public static string connectionString = Properties.Settings.Default.connectionString;
public static SqlDataReader executeReader(string query)
{
SqlDataReader result = null;
System.Diagnostics.Debug.WriteLine("FoodBankDB executeReader: " + query);
SqlConnection connection = new SqlConnection(connectionString);
SqlCommand command = new SqlCommand(query, connection);
connection.Open();
result = command.ExecuteReader();
connection.Close();
return result;
}
}
我将它们分成两个类,以便每当我的连接字符串更改时,我可以通过更改FoodBankDB类来轻松修改整个项目。
这是我的业务逻辑层:
public List<Distribution> getAllScheduledDistribution()
{
List<Distribution> allDistribution = new List<Distribution>();
Distribution distributionDAL = new Distribution();
allDistribution = distributionDAL.getDistributionAll();
return allDistribution;
}
最后但同样重要的是,我的演示层:
List<Distribution> scheduledList = new List<Distribution>();
scheduledList = packBLL.getAllScheduledDistribution();
ddlScheduleList.DataSource = scheduledList;
ddlScheduleList.DataTextField = "address";
ddlScheduleList.DataValueField = "address";
ddlScheduleList.DataBind();
如果我没有把数据访问层和连接字符串类分开,它就能正常工作。有人知道如何解决这个错误吗?
提前致谢。
更新部分
public static string GetConnectionString()
{
return connectionString;
}