在 if-else 语句中，在 else 之前退出 datareader

Question

我想找到一种在 if 语句之后退出 datareader 的方法，以便我可以在 else 语句中执行插入查询。有办法吗？

我收到 dr 仍处于打开状态的错误，因此无法执行以下查询。

sVendorDetails.VendorID = insertcmd.ExecuteNonQuery();

代码如下：

public class VendorDetails
{
    int _VendorID;
    string _VendorName;

    public int VendorID
    {
        set { _VendorID = value; }
        get { return _VendorID; }
    }

    public string VendorName
    {
        set { _VendorName = value; }
        get { return _VendorName; }
    }
}

public VendorDetails VendorCheck(string sVendorName)
{
    SqlCommand cmd = new SqlCommand("dbo.usp_GetVendorByVendorName", myConnection);
    cmd.CommandType = CommandType.StoredProcedure;
    cmd.Parameters.Add(new SqlParameter("@VendorName", SqlDbType.VarChar));
    cmd.Parameters["@VendorName"].Value = sVendorName;
    VendorDetails sVendorDetails = null;

    try
    {
        myConnection.Open();
        SqlDataReader dr = cmd.ExecuteReader();
        if (dr.HasRows)
        {
            while (dr.Read())
            {
                sVendorDetails = new VendorDetails();
                sVendorDetails.VendorID = ((int)dr["VendorID"]);
                sVendorDetails.VendorName = ((string)dr["VendorName"]).ToUpper().Trim();
            }
        } 
        else if (dr.HasRows!= true)
        {
            ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('VendorName:" + sVendorName + " not found. Inserting Vendor details into Vendor and Invoice table.')", true);
            SqlCommand insertcmd = new SqlCommand("dbo.InsertVendorName", myConnection);
            insertcmd.CommandType = CommandType.StoredProcedure;
            insertcmd.Parameters.Add(new SqlParameter("@VendorName", SqlDbType.VarChar));
            insertcmd.Parameters["@VendorName"].Value = sVendorName;
            sVendorDetails = new VendorDetails();
            sVendorDetails.VendorID = insertcmd.ExecuteNonQuery();
            sVendorDetails.VendorName = sVendorName;
        }

        dr.Close(); 
        return sVendorDetails;

        }
        catch (SqlException err)
        {
            throw new ApplicationException("DB usp_GetVendorByVendorName Error: " + err.Message);
        }

        finally
        {
            myConnection.Close();
        }
    }

Answer 1

您需要在重新使用连接之前关闭/处置您的 DataReader，因为它仍在使用中。

也许是这样的？

var readerHasRows = false;

using (var dr = cmd.ExecuteReader())
{
    readerHasRows = dr.HasRows;

    if(readerHasRows)
    {
        while (dr.Read())
        {
            sVendorDetails = new VendorDetails();
            sVendorDetails.VendorID = ((int)dr["VendorID"]);
            sVendorDetails.VendorName = ((string)dr["VendorName"]).ToUpper().Trim();
        }
    }
}

if(!readerHasRows)
{
    ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('VendorName:" + sVendorName + " not found. Inserting Vendor details into Vendor and Invoice table.')", true);
    SqlCommand insertcmd = new SqlCommand("dbo.InsertVendorName", myConnection);
    insertcmd.CommandType = CommandType.StoredProcedure;
    insertcmd.Parameters.Add(new SqlParameter("@VendorName", SqlDbType.VarChar));
    insertcmd.Parameters["@VendorName"].Value = sVendorName;
    sVendorDetails = new VendorDetails();
    VendorDetails.VendorID = insertcmd.ExecuteNonQuery();
    sVendorDetails.VendorName = sVendorName;
}

Answer 2

有几点我想说

1. 您的主要问题是您没有关闭您的DataReader。你可以使用using 声明它
2. 您无需显式打开和关闭SqlConnection。 SqlCommand 对象将根据需要执行此操作。
3. 您无需检查if (dr.HasRows)，然后再次检查while (dr.Read())。此外，您无需循环即可仅获取一行数据。
4. 理想情况下，我会将“Fetch”部分放在单独的函数中，将“插入”部分放在单独的函数中，这样函数就可以保持小且可重复使用。
5. 你的模式是多余的if (flag) {TakeAction();} else if (!flag) {TakeAction2();}. Every time the code hits theelse, it will also hit theif (!flag)`
6. sVendorDetails.VendorID = insertcmd.ExecuteNonQuery(); 行看起来很可疑。如果您的存储过程返回VendorId，那么您应该使用ExecuteScalar。目前它在所有情况下都只是存储1，因为您可能正在插入一行。
7. 创建自定义ApplicationException 时不要丢弃原始SqlException。上游系统可能想知道比您传递的更多细节。将其作为InnerException 传递
8. 我还改变了一些风格方面：
   1. 变量名改为更常用的camelCase，而不是错误使用的Hungarian Notation（sVendorDetails而不是oVendorDetails）
   2. K&R 风格的大括号
   3. 当右侧是new 语句时使用var
   4. 使用对象初始化器而不是创建+赋值

下面是代码

public VendorDetails VendorCheck(string vendorName, SqlConnection myConnection) {
    try {
        return GetVendor(vendorName, myConnection) ?? InsertVendor(vendorName, myConnection);
    } catch (SqlException err) {
        throw new ApplicationException("DB usp_GetVendorByVendorName Error: " + err.Message, err);
    }
}

VendorDetails GetVendor(string vendorName, SqlConnection myConnection) {
    using (var cmd = new SqlCommand("dbo.usp_GetVendorByVendorName", myConnection)) {
        cmd.CommandType = CommandType.StoredProcedure;
        cmd.Parameters.Add(new SqlParameter("@VendorName", SqlDbType.VarChar));
        cmd.Parameters["@VendorName"].Value = vendorName;

        using (SqlDataReader dr = cmd.ExecuteReader()) {
            ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('VendorName:" + vendorName + " not found. Inserting Vendor details into Vendor and Invoice table.')", true); // TODO: Does this really belong here!?!?
            if (dr.Read()) {
                return new VendorDetails {
                    VendorID = ((int)dr["VendorID"]),
                    VendorName = ((string)dr["VendorName"]).ToUpper().Trim()
                };
            }
        }
    }

    return null;
}

VendorDetails InsertVendor(string vendorName, SqlConnection myConnection) {
    using (var insertcmd = new SqlCommand("dbo.InsertVendorName", myConnection)) {
        insertcmd.CommandType = CommandType.StoredProcedure;
        insertcmd.Parameters.Add(new SqlParameter("@VendorName", SqlDbType.VarChar));
        insertcmd.Parameters["@VendorName"].Value = vendorName;
        return new VendorDetails {
            VendorID = (int)insertcmd.ExecuteScalar(),
            VendorName = vendorName
        };
    }
}