对sqlcommand.executescalar使用说明

Question

我正在使用using语句来验证客户编号。

using (SqlConnection connection = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString))
{
    connection.Open();

    using (SqlCommand cmdCheck = new SqlCommand("SELECT COUNT(CUSTOMER_NO) FROM WEBSITE_CUSTOMERS WHERE UPPER(CUSTOMER_NO) = '" + strCustomer.Trim().ToUpper() + "';", connection))
    {
        int nExists = (int)cmdCheck.ExecuteScalar();
        if (nExists > 0) 
            return true;
        else
            return false;
    }
}

这是以前在stackoverflow上向我建议的用于检查预先存在的记录的代码...虽然效果很好，但是我想知道是否有一种方法可以将参数用于客户编号，因为此变量是通过表单输入的，我想保护它免受注射。 当这样的using语句中的cmdCheck参数在哪里创建？

Answer 1

初始化命令后，添加参数。 一个便捷的方法是AddWithValue ：

const string sql = @"SELECT 
                        COUNT(CUSTOMER_NO) 
                     FROM 
                        WEBSITE_CUSTOMERS 
                     WHERE 
                        UPPER(CUSTOMER_NO) = @CUSTOMER_NO;";

using (SqlConnection connection = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString))
{
    using (SqlCommand cmdCheck = new SqlCommand(sql, connection))
    {
        cmdCheck.Parameters.AddWithValue("@CUSTOMER_NO", strCustomer.Trim().ToUpper());
        connection.Open();
        int nExists = (int)cmdCheck.ExecuteScalar();
        return nExists > 0;
    }
}