Bdtjtk

I have a login form that I wanna select the userID (which is in the form of an int) from the database, and store it as a string.

string insertQuery = 

  "SELECT UserID FROM Customers WHERE Email = @Email AND Password = @Password";



SqlCommand com = new SqlCommand(insertQuery, conn);



com.Parameters.AddWithValue("@Email", tbEmail.Text);

com.Parameters.AddWithValue("@Password", tbPassword.Text);



string result = (string)com.ExecuteScalar();

But after I login, I get this error:

System.InvalidCastException: 'Unable to cast object of type
'System.Int32' to type 'System.String'.

You can try using like below

string result = Convert.ToString(com.ExecuteScalar());

What if the record doesn't exist (i.e. the cursor is empty)? Let's read and check if we have at least one record:

// Keep Sql being readable

string insertQuery = 

  @"SELECT UserID 

      FROM Customers 

     WHERE Email = @Email 

       AND Password = @Password";



// Do not forget to dispose IDisposable

using (SqlCommand com = new SqlCommand(insertQuery, conn)) {

  com.Parameters.AddWithValue("@Email", tbEmail.Text);

  com.Parameters.AddWithValue("@Password", tbPassword.Text);



  using (var reader = com.ExecuteReader()) {

    string result = reader.Read()

      ? Convert.ToString(reader[0]) // record exists

      : null;                       // cursor is empty



    //TODO: put relevant code which works with result here

  }

}

ExecuteScalar returns Object type and you can convert it into which ever type you like

public override object ExecuteScalar ();

You can call it's ToString() method and it returns string form of it's value.

Try this,

string result = string.Empty;



SqlCommand com = new SqlCommand(..);

..

object executedResult = com.ExecuteScalar();



if(executedResult != null) {

   result = executedResult.ToString();

}

Hope helps,

Probably the simplest solution would be (assuming query always return result):

string result = com.ExecuteScalar().ToString();

You can cast as nvarchar in your query also:

string insertQuery = "SELECT cast(UserID as nvarchar) FROM Customers WHERE Email = @Email AND Password = @Password";

Below are my findings

    string userID;



using(SqlConnection conn = new SqlConnection(connectionString))

{

            string insertQuery = "SELECT UserID FROM Customers WHERE Email = @Email AND 

            Password = @Password";

            SqlCommand com = new SqlCommand(insertQuery, conn);

            com.CommandType = CommandType.StoredProcedure;

            com.Parameters.AddWithValue("@Email", tbEmail.Text.ToString().Trim());

            com.Parameters.AddWithValue("@Password", tbPassword.Text.ToString().Trim());

            SqlDataReader reader = com.ExecuteReader();

            while(reader.Read())

            {

              userID = reader["UserID"].ToString();

            }

}