检查用户是否已存在于带有C#的MySql数据库中
本文关键字:MySql 数据库 于带 用户 是否 存在 检查 | 更新日期: 2023-09-27 18:21:34
我有以下代码,我希望该代码能查询数据库:
MySqlConnection connection = new MySqlConnection(Connection);
MySqlCommand cmd;
connection.Open();
try
{
cmd = connection.CreateCommand();
cmd.CommandText = ("INSERT INTO edata (username) VALUES ('" + this.NewUserName.Text +"') ;");
MySqlDataReader myReader;
myReader = cmd.ExecuteReader();
loading.Show();
MessageBox.Show("Your Account Has Been Created!!");
connection.Close();
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
如果客户端输入(NewUserName.Text)与数据库中的用户名相同,则应显示错误消息,否则将出现重复的用户名。我该怎么做?
我已经将连接作为字符串。
提前感谢!!!
附言:我是一名学习C#和MySql的学生,我很感激你的帮助和建议!
您可以在数据库中的username字段上创建一个Unique Constraint,如果用户已经存在,这将引发异常。
或者,您可以从表中手动选择,并在插入之前查看是否有同名用户。
您可以在适当的列(doc)上创建唯一索引。
CREATE UNIQUE INDEX uq_username ON edata (username);
您正在使用成员类吗?
MembershipCreateStatus createStatus;
MembershipUser newUser = Membership.CreateUser(txtEmail.Text, "password", txtEmail.Text,"What was your first school?","idk", true, out createStatus);
switch (createStatus)
{
case MembershipCreateStatus.Success:
//do your actions here
case MembershipCreateStatus.DuplicateUserName:
CreateAccountResults.Text = "There already exists a user with this username.";
break;
case MembershipCreateStatus.DuplicateEmail:
CreateAccountResults.Text = "There already exists a user with this email address.";
break;
case MembershipCreateStatus.InvalidEmail:
CreateAccountResults.Text = "There email address you provided in invalid.";
break;
case MembershipCreateStatus.InvalidAnswer:
CreateAccountResults.Text = "There security answer was invalid.";
break;
case MembershipCreateStatus.InvalidPassword:
CreateAccountResults.Text = "The password you provided is invalid. It must be seven characters long and have at least one non-alphanumeric character.";
break;
default:
CreateAccountResults.Text = "There was an unknown error; the user account was NOT created.";
break;
}
如果你没有使用它,那么只需创建一个读取数据库的方法,并在上面的代码之前调用它:
string doesuserexist = ReadDatabase("Select Email from Patients where Email=@emailaddress").TrimEnd();
if (checkemail != "")
{
CreateAccountResults.Text = "User Email Already Exists";
return;
}
您必须编写自己的ReadDatabase方法,但从上面发布的代码中,您显然知道如何使用select替换insert sql语句。