从用户名和密码输入中获取主键

Question

I have a table which consists of id username and password. I currently have a wpf form which asks the user for username and password and if they exist in the table the person can log in. After they have logged in it leads them to another table and form in which they can add data.

My question is how can i get the pk of the login information used and add it it to the table on the next form?

Edit: on the second table i already have a column dedicated for the pk of the username and password table Edit2:

The table which stores the login information is as follows

ID - username - password
1   - ish - 1234
2  - tom - abc
3  - jeff - qwerty
etc

i want to be able to retrieve the id when i login in though two textbooks

eg if i type "tom" then type "abc" i should be able to the id of 2

Answer 1

Well you get the id from which they log in and pass it to the other form:

using(Sqlconnection con = new SqlConnection(constr))
{
     using(SqlCommand cmd = new SqlCommand("select id from Users where username = @username and password = @password", con)
     {
          cmd.Paramters.Add("@username", SqlDbType.VarChar).Value = username;
          cmd.Paramters.Add("@password", SqlDbType.VarChar).Value = password;
          con.Open();
          string result = (string)cmd.ExecuteScalar();
          if(result!=null)
          {
              int id = int.Parse(result);
              SecondForm frm = new SecondForm();
              frm.UserId = id;
              frm.Show();
          }
          else
          {
              //tell the user that credentials are not valid
          }
     }
}

In your second form you should have a property like:

public int UserId {get; set;} = 0;

Answer 2

In this case it is better to write a stored procedure that takes username & password and returns the primary key if valid else -1. Call the the SP from the code and if the return value is greater than 0 then it is the primary key.

How you pass this id to next form depends on the technology you use. It can be passed as query string, not recommended though, post as form field, Session variable, etc.

There are lot of scope for improvement in this design though. But it is better to follow some basic things like

In the second table the column that stores the primary key (id) of first table should be a foreign key referencing primary key of first table. Technically it doesn't have to be a foreign key but it is best approach.

Another suggestion is to store the password as hash instead of direct text. A hash with salt is lot safer.