Question

我想找到一种方法在if语句之后退出datareader，这样我就可以在else语句中执行insert查询。有办法吗？

我收到dr仍然打开的错误，因此无法执行以下查询。

sVendorDetails.VendorID = insertcmd.ExecuteNonQuery();

以下是代码：

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

在重新使用连接之前，您需要关闭/丢弃DataReader，因为它仍然在使用。

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

我想提一些事情

您的主要问题是您没有关闭DataReader。您可以使用using语句
您不需要明确打开和关闭SqlConnection。 SqlCommand对象将根据需要执行此操作。
您不需要查看if (dr.HasRows)，然后再次查看while (dr.Read())。此外，您不需要循环只选择一行数据。
理想情况下，我会把＆＃34; Fetch＆＃34;部分在一个单独的功能和＆＃34;插入＆＃34;在一个单独的功能中，功能保持小巧且可重复使用。
你的模式是多余的if (flag) {TakeAction（）;}否则if（！flag）{TakeAction2（）;} . Every time the code hits the else , it will also hit the if（！flag）`
sVendorDetails.VendorID = insertcmd.ExecuteNonQuery();看起来很腥。如果您的存储过程返回VendorId，那么您应该使用ExecuteScalar。目前它只是在所有情况下存储1，因为你可能会插入一行。
创建自定义SqlException时，不要丢弃原始ApplicationException。上游系统可能想知道比你传递的更多细节。将其作为InnerException
我也改变了一些风格方面：
1. 变量名称更改为更常用的camelCase，而不是错误使用的Hungarian Notation（sVendorDetails而不是oVendorDetails）
2. 支持K＆amp; R风格
3. 当右侧是var语句
4. 使用对象初始值设定项而不是创建+赋值

以下是代码

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
        };
    }
}

在if-else语句之前退出datareader

2 个答案: