Running a query and displaying result it in a TEdit

Question

I have a TComboBox containing a list of names gathered from my database. Next to it is a TEdit that I intend on using for the purposes for displaying the ID number associated to each person.

Since firstName and lastName are separate fields within the table, but displayed together in the TCombobox I have written a small section to split the firstName and lastName into two separate variables:

 pos := AnsiPos(' ', cbStudents.Text); 
 firstName := Copy(cbStudents.Text, 0, pos-1);
 lastName := Copy(cbStudents.Text, pos+1, Length(cbStudents.Text));

Then I execute the SQL code:

  try
    query.Open;
    query.SQL.Add('Select studentID');
    query.SQL.Add('From student');
    query.SQL.Add('Where firstName = ' + StrToQuote(firstName));
    query.SQL.Add('And lastName = ' + StrToQuote(lastName));
    editID.Text := query
  finally
    query.Free;
  end;

Note: StrToQuote encapsulates the variable firstName and lastName with double quotes (" ")

The error that I am receiving is:

Argument out of range

What am I doing wrong? Thank you in advanced for the help.

Answer 1

Your code can not work. It opens the query first, then it sets the SQL query string. Instead of

   try
     query.Open;
     query.SQL.Add('Select studentID');
     query.SQL.Add('From student');
     query.SQL.Add('Where firstName = ' + StrToQuote(firstName));
     query.SQL.Add('And lastName = ' + StrToQuote(lastName));
   finally
     query.Free;
   end;

use

  // create or reset query here
  query := ...

  try

    query.SQL.Add('SELECT studentID');
    query.SQL.Add('FROM student');
    query.SQL.Add('WHERE firstName = :firstname');
    query.SQL.Add('AND lastName = :lastName');

    // set parameter values here

    query.Open;

    // now transfer data from fields to the user interface (TEdit)

  finally
    query.Free;
  end;

Answer 2

Your approach does not seam optimal for me (splitting Displayed Name), but your problem here would be accessing query.Fields[0].AsString after freeing the query.