Question

好的，我很难用这个，我花了几天时间与谷歌等人试图找出我搞砸的地方。

我对C＃非常陌生，而我正在做的是尝试抓取Customer_ID (Primary Key)从我的SQL Server中添加1，然后输入该值作为下一个客户ID。如果我取出将值添加到Customer_ID字段的部分，我会收到一条错误消息，说我无法插入空值。任何帮助将不胜感激。

错误是：

必须声明标量变量＆＃34; @ custID＆＃34;。

这是我的代码：

string firstName = fName.Text;
string lastName = lName.Text;
string address1 = address.Text;
string city = addressCity.Text;
string state = addressState.Text;
string zip1 = addressZip.Text;
string phoneNum = phone.Text;
string emailadd = custEmail.Text;
int finalCustID = 0;

SqlCommand getMaxCustID = new SqlCommand("SELECT MAX(Customer_ID) FROM dbo.Customers", Form1.sqlConnection);
getMaxCustID.Parameters.AddWithValue("@custID", finalCustID);
Int32 count = Convert.ToInt32(getMaxCustID.ExecuteScalar());
finalCustID = (int)count + 1;
//Int32 newCustID = count + 1;

SqlCommand saveRecord = new SqlCommand("INSERT INTO dbo.Customers (Customer_ID,First_Name, Last_Name, Customer_Address,City,St,Zip,Phone,Email)" + "Values (@custID'firstName','lastName','address1','city','state','zip1','phoneNum','emailadd')", Form1.sqlConnection);

Console.Write(" This is the final ID " + finalCustID + " \n");
try
{
    saveRecord.ExecuteNonQuery();
}
catch (Exception ex)
{ 
    Console.WriteLine(ex.Message);
    Console.Write(saveRecord);
}

这是我最终的结果。我不认为它是最好的，但它正常工作。谢谢大家的帮助：

        string firstName = fName.Text;
        string lastName = lName.Text;
        string address1 = address.Text;
        string city = addressCity.Text;
        string state = addressState.Text;
        string zip1 = addressZip.Text;
        string phoneNum = phone.Text;
        string emailadd = custEmail.Text;
        int finalCustID = 0;

        SqlCommand getMaxCustID = new SqlCommand("SELECT MAX(Customer_ID) FROM dbo.Customers", Form1.sqlConnection);
        //getMaxCustID.Parameters.AddWithValue("@custID", finalCustID);
        Int32 count = Convert.ToInt32(getMaxCustID.ExecuteScalar());
        finalCustID = (int)count + 1;
        //Int32 newCustID = count + 1;

        SqlCommand saveRecord = new SqlCommand("INSERT INTO dbo.Customers " + "(Customer_ID,First_Name, Last_Name, Customer_Address,City,St,Zip,Phone,Email)" + " Values (@custID,@fName,@lName,@address,@city,@state," + "@zip,@phoneNumber,@custEmail)", Form1.sqlConnection); ;
        Console.Write(" This is the final ID " + finalCustID + " \n");
        try
        {
            saveRecord.Parameters.AddWithValue("@custID", finalCustID);
            saveRecord.Parameters.AddWithValue("@fName", firstName);
            saveRecord.Parameters.AddWithValue("@lName", lastName);
            saveRecord.Parameters.AddWithValue("@address", address1);
            saveRecord.Parameters.AddWithValue("@city", city);
            saveRecord.Parameters.AddWithValue("@state", city);
            saveRecord.Parameters.AddWithValue("@zip", zip1);
            saveRecord.Parameters.AddWithValue("@phoneNumber", phoneNum);
            saveRecord.Parameters.AddWithValue("@custEmail", emailadd);

            saveRecord.ExecuteNonQuery();
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.Message);
            Console.Write(saveRecord);
        }

Answer 1

您正在为命令添加参数，但您根本没有在命令文本中指定它。

SqlCommand getMaxCustID = new SqlCommand("SELECT MAX(Customer_ID) FROM dbo.Customers",
                                  Form1.sqlConnection);
//getMaxCustID.Parameters.AddWithValue("@custID", finalCustID); //Comment that out

由于您未使用参数@custID，因此无需将其传递给命令。只需注释掉或删除该行。

稍后您在yoru insert语句中使用参数@custID，您需要将参数添加到该命令对象。

saveRecord.Parameters.AddWithValue("@custID", finalCustID);

（感谢@ N55PEC），您在参数和下一个值之间的INSERT命令文本中缺少逗号。应该是这样的：

注意：其他格式用于在视口中保留答案。

SqlCommand saveRecord = new SqlCommand("INSERT INTO dbo.Customers " +
       "(Customer_ID,First_Name, Last_Name, Customer_Address,City,St,Zip,Phone,Email)" + 
       " Values (@custID,'firstName','lastName','address1','city','state'," +
       "'zip1','phoneNum','emailadd')", Form1.sqlConnection);

Answer 2

需要@custID参数的命令名为saveRecord，您将其添加到名为getMaxCustID

的命令中

SqlCommand getMaxCustID = new SqlCommand("SELECT MAX(Customer_ID) FROM dbo.Customers", Form1.sqlConnection);
Int32 count = Convert.ToInt32(getMaxCustID.ExecuteScalar());
finalCustID = (int)count + 1;

SqlCommand saveRecord = new SqlCommand("INSERT INTO dbo.Customers (Customer_ID,First_Name, Last_Name, Customer_Address,City,St,Zip,Phone,Email)" + "Values (@custID', firstName','lastName','address1','city','state','zip1','phoneNum','emailadd')", Form1.sqlConnection);
saveRecord.Parameters.AddWithValue("@custID", finalCustID);

但是，正如我在上面的评论中所说的那样，在多用户环境中使用MAX来检索下一个要分配给下一个客户的号码显然是错误的。如果，另一个用户在执行读取客户ID和插入新记录之间添加客户时会怎样？您将以主键违规例外结束。

使用此方案的最佳方法是将Customer_ID列作为IDENTITY列，然后编写此类代码

SqlCommand saveRecord = new SqlCommand(@"INSERT INTO dbo.Customers 
       (First_Name, Last_Name, Customer_Address,City,St,Zip,Phone,Email)
        Values (@custID,'firstName','lastName','address1','city','state','zip1',
       'phoneNum','emailadd');
       SELECT SCOPE_IDENTITY()", Form1.sqlConnection);
int newCustomerID = Convert.ToInt32(saveRecord.ExecuteScalar());

请注意，如果您将Customer_ID作为IDENTITY列，则不应尝试为其传递值，但可以使用SELECT SCOPE_IDENTITY()

检索数据库引擎分配的值

Answer 3

按原样使用以下行：

SqlCommand getMaxCustID = new SqlCommand("SELECT MAX(Customer_ID) FROM dbo.Customers", Form1.sqlConnection);
Int32 count = Convert.ToInt32(getMaxCustID.ExecuteScalar());

执行：

int finalCustID = (int)count + 1;

然后：

SqlCommand saveRecord = new SqlCommand("INSERT INTO dbo.Customers (Customer_ID,First_Name, Last_Name, Customer_Address,City,St,Zip,Phone,Email)" + "Values ('finalCustID.toString() ','firstName','lastName','address1','city','state','zip1','phoneNum','emailadd')", Form1.sqlConnection);

最后：

saveRecord.ExecuteNonQuery();

必须声明标量变量？

3 个答案: