Question

我正在使用带有C＃的ASP.net来创建用户记录。在下面的代码中，如何设置条件以检测用户名是否已存在。

try
{
    Guid newGuid = Guid.NewGuid();

    SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString);
    conn.Open();

    string insertQuery = "insert into UsrData (Id, UserName, Email, Password, Country) values (@id, @Uname, @email, @password, @country)";

    SqlCommand com = new SqlCommand(insertQuery, conn);

    com.Parameters.AddWithValue("@id", newGuid);
    com.Parameters.AddWithValue("@Uname", TextBoxUN.Text);
    com.Parameters.AddWithValue("@email", TextBoxEmail.Text);
    com.Parameters.AddWithValue("@password", TextBoxPass.Text);
    com.Parameters.AddWithValue("@country", DropDownListCountry.SelectedItem.ToString());

    com.ExecuteNonQuery();

    Response.Redirect("login.aspx");
    Response.Write("Sucessuflly registred");

    conn.Close();
}
catch (Exception ex)
{
    Response.Write("An unknown error " + ex.ToString());
}

Answer 1

在SQL代码中放置一个存在条件：

try
{
  Guid newGuid = Guid.NewGuid();

  SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString);
  conn.Open();

  string insertQuery = @"if not exists (select * from UsrData where UserName = @Uname)
    insert into UsrData (Id, UserName, Email, Password, Country) values (@id, @Uname, @email, @password, @country)";
  SqlCommand com = new SqlCommand(insertQuery, conn);

    com.Parameters.AddWithValue("@id", newGuid);
    com.Parameters.AddWithValue("@Uname", TextBoxUN.Text);
    com.Parameters.AddWithValue("@email", TextBoxEmail.Text);
    com.Parameters.AddWithValue("@password", TextBoxPass.Text);
    com.Parameters.AddWithValue("@country", DropDownListCountry.SelectedItem.ToString());

    com.ExecuteNonQuery();

    Response.Redirect("login.aspx");
    Response.Write("Sucessuflly registred");

    conn.Close();
}
catch (Exception ex)
{
    Response.Write("An unknown error " + ex.ToString());
}

Answer 2

取决于用户名检查是否应该扩展到整个表格，或者只是这一个语句（在这种情况下，Frank的回答是正确的）。

根据您使用的DBMS，您可以针对UserName列定义UNIQUE key/constraint，这将保证唯一性。但是，在应用此约束之前，您需要确保表中当前的所有用户名都是唯一的。

用户帐户用户名条件

2 个答案: