C# ASP.NETC-基于条件设置MySQL查询和参数
如何根据条件设置MySQL查询和参数 我想要基于“questionSource”的不同查询,如下所示 但是,在我下面的代码中,“cmd”在当前上下文中不存在 或者,我可以为每个条件使用两个不同的函数,并根据需要调用必要的函数,但我认为一定有一种方法可以在连接中使用条件C# ASP.NETC-基于条件设置MySQL查询和参数,c#,mysql,asp.net,parameters,ado.net,C#,Mysql,Asp.net,Parameters,Ado.net,如何根据条件设置MySQL查询和参数 我想要基于“questionSource”的不同查询,如下所示 但是,在我下面的代码中,“cmd”在当前上下文中不存在 或者,我可以为每个条件使用两个不同的函数,并根据需要调用必要的函数,但我认为一定有一种方法可以在连接中使用条件 //validation checks else { string connStr = ConfigurationManager.ConnectionStrings["myConnectionString"].Connec
//validation checks
else
{
string connStr = ConfigurationManager.ConnectionStrings["myConnectionString"].ConnectionString;
MySqlConnection conn = new MySqlConnection(connStr);
string questionSource = Session["QuestionSource"].ToString();
string cmdText = "";
if (questionSource.Equals("S"))
{
cmdText += @"SELECT COUNT(*) FROM questions Q
JOIN users U
ON Q.author_id=U.user_id
WHERE approved='Y'
AND role=1
AND module_id=@ModuleID";
MySqlCommand cmd = new MySqlCommand(cmdText, conn);
cmd.Parameters.Add("@ModuleID", MySqlDbType.Int32);
cmd.Parameters["@ModuleID"].Value = Convert.ToInt32(Session["TestModuleID"]);
}
else if (questionSource.Equals("U"))
{
cmdText += "SELECT COUNT(*) FROM questions WHERE approved='Y' AND module_id=@ModuleID AND author_id=@AuthorID;";
MySqlCommand cmd = new MySqlCommand(cmdText, conn);
cmd.Parameters.Add("@ModuleID", MySqlDbType.Int32);
cmd.Parameters["@ModuleID"].Value = Convert.ToInt32(Session["TestModuleID"]);
cmd.Parameters.Add("@AuthorID", MySqlDbType.Int32);
cmd.Parameters["@AuthorID"].Value = Convert.ToInt32(Session["UserID"]);
}
int noOfQuestionsAvailable = 0;
int noOfQuestionsWanted = Convert.ToInt32(ddlNoOfQuestions.SelectedValue);
try
{
conn.Open();
noOfQuestionsAvailable = Convert.ToInt32(cmd.ExecuteScalar());
if (noOfQuestionsAvailable < noOfQuestionsWanted)
{
lblError.Text = "There are not enough questions available to create a test.";
}
else
{
Session["TestName"] = txtName.Text;
Session["NoOfQuestions"] = ddlNoOfQuestions.SelectedValue;
Session["QuestionSource"] = rblQuestionSource.SelectedValue;
Session["TestModuleID"] = ddlModules.SelectedValue;
Response.Redirect("~/create_test_b.aspx");
}
}
catch
{
lblError.Text = "Database connection error - failed to get module details.";
}
finally
{
conn.Close();
}
}
您只需将cmd的声明移到if块之外:
//validation checks
else
{
string connStr = ConfigurationManager.ConnectionStrings["myConnectionString"].ConnectionString;
MySqlConnection conn = new MySqlConnection(connStr);
string questionSource = Session["QuestionSource"].ToString();
string cmdText = "";
MySqlCommand cmd; // <-- here
if (questionSource.Equals("S"))
{
cmdText += @"SELECT COUNT(*) FROM questions Q
JOIN users U
ON Q.author_id=U.user_id
WHERE approved='Y'
AND role=1
AND module_id=@ModuleID";
cmd = new MySqlCommand(cmdText, conn); // remove MySqlCommand here
cmd.Parameters.Add("@ModuleID", MySqlDbType.Int32);
cmd.Parameters["@ModuleID"].Value = Convert.ToInt32(Session["TestModuleID"]);
}
else if (questionSource.Equals("U"))
{
cmdText += "SELECT COUNT(*) FROM questions WHERE approved='Y' AND module_id=@ModuleID AND author_id=@AuthorID;";
cmd = new MySqlCommand(cmdText, conn); // remove MySqlCommand here
cmd.Parameters.Add("@ModuleID", MySqlDbType.Int32);
cmd.Parameters["@ModuleID"].Value = Convert.ToInt32(Session["TestModuleID"]);
cmd.Parameters.Add("@AuthorID", MySqlDbType.Int32);
cmd.Parameters["@AuthorID"].Value = Convert.ToInt32(Session["UserID"]);
}
int noOfQuestionsAvailable = 0;
int noOfQuestionsWanted = Convert.ToInt32(ddlNoOfQuestions.SelectedValue);
try
{
conn.Open();
noOfQuestionsAvailable = Convert.ToInt32(cmd.ExecuteScalar());
if (noOfQuestionsAvailable < noOfQuestionsWanted)
{
lblError.Text = "There are not enough questions available to create a test.";
}
else
{
Session["TestName"] = txtName.Text;
Session["NoOfQuestions"] = ddlNoOfQuestions.SelectedValue;
Session["QuestionSource"] = rblQuestionSource.SelectedValue;
Session["TestModuleID"] = ddlModules.SelectedValue;
Response.Redirect("~/create_test_b.aspx");
}
}
catch
{
lblError.Text = "Database connection error - failed to get module details.";
}
finally
{
conn.Close();
}
}
只要将MySqlCommand的声明移到if/else块之外,就可以在执行命令的最后一次尝试中使用它
//validation checks
else
{
string connStr = ConfigurationManager.ConnectionStrings["myConnectionString"].ConnectionString;
using(MySqlConnection conn = new MySqlConnection(connStr))
using(MySqlCommand cmd = conn.CreateCommand())
{
// Don't need to associate the command to the connection
// Already done by the CreateCommand above, just need to set
// the parameters and the command text
if (questionSource.Equals("S"))
{
cmdText = @"....."
cmd.CommandText = cmdText;
....
}
else if (questionSource.Equals("U"))
{
cmdText = "........."
cmd.CommandText = cmdText;
....
}
try
{
conn.Open();
noOfQuestionsAvailable = Convert.ToInt32(cmd.ExecuteScalar());
....
}
}
}
还请注意,您应该使用using语句来确保您的连接和命令已正确关闭和释放。在if之前声明cmd
MySqlCommand cmd = new MySqlCommand("",connStr);
在if的每个部分
cmd.CommandText=cmdText;
其他建议:添加
cmd.Parameters.Add("@ModuleID", MySqlDbType.Int32);
cmd.Parameters["@ModuleID"].Value = Convert.ToInt32(Session["TestModuleID"]);
始终在if之前,因为它在if和else部分中以相同的方式使用完成,尽管我在下面的行中得到了“使用未分配的局部变量”cmd-“noOfQuestionsAvailable=Convert.ToInt32cmd.ExecuteScalar;”您可以将其初始化为null,如MySqlCommand cmd=null;如果在else块之后cmd仍然为null,则提前中止。我在下面的行中得到“使用未分配的局部变量”cmd-“noofquestionsavable=Convert.ToInt32cmd.ExecuteScalar;”