Forming a variable name with string + integer and calling functions

Question

Firstly, I am new to these and the question could be stupid. Anyway, I have a procedure like this:

procedure Tform1.QueryChange(sqltext : String; query : Integer);
begin
if query = 1 then begin
ADOQuery1.Close;
ADOQuery1.SQL.Clear;
ADOQuery1.SQL.Add(sqltext);
ADOQuery1.Open;
end;
if query = 2 then begin
ADOQuery2.Close;
ADOQuery2.SQL.Clear;
ADOQuery2.SQL.Add(sqltext);
ADOQuery2.Open;
end;

I would like to remove the if blocks and make one united code:

ADOQuery+query.Close; (know that looks very silly)
ADOQuery+query.SQL.Clear;
ADOQuery+query.SQL.Add(sqltext);
ADOQuery+query.Open;

My goal is when query=1 code will use ADOQuery1.Close; etc. when query=2 code will use ADOQuery2.Close;

only from curiosity , why not QueryChange(const sqltext : String; query : TAdoQuery); ? — bummi
– bummi, Commented May 23, 2013 at 11:10

David Heffernan · Accepted Answer · 2013-05-23 09:30:02Z

8

You could create a local variable that referred to the TADOQuery object that you wish to operate on. Like this:

var
  ADOQuery: TADOQuery;
begin
  if query=1 then
    ADOQuery := ADOQuery1
  else if query=2 then
    ADOQuery := ADOQuery2;
  ADOQuery.Close;
  ADOQuery.SQL.Clear;
  ADOQuery.SQL.Add(sqltext);
  ADOQuery.Open;      
end;

answered May 23, 2013 at 9:30

David Heffernan

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Andreas Rejbrand · Accepted Answer · 2013-05-23 09:29:59Z

6

Instead of creating variables ADOQuery1, ADOQuery2, ADOQuery3 etc of type TADOQuery, create an array:

ADOQueries: array of TADOQuery;

Then set the number of elements in it, when you know how many they will be:

SetLength(ADOQueries, NumberOfQueries);

Alternatively, if you know from the beginning how many elements there will be, you can define ADOQueries to be a static array instead:

ADOQueries: array[0..7] of TADOQuery;

Now you can do

procedure TForm1.QueryChange(sqltext: String; query: Integer);
begin
  ADOQueries[Query].Close;
  ADOQueries[Query].SQL.Clear;
  ADOQueries[Query].SQL.Add(sqltext);
  ADOQueries[Query].Open;
end;

answered May 23, 2013 at 9:29

Andreas Rejbrand

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8 Comments

David Heffernan Over a year ago

If you want to talk about elegance, I'd draw attention to the repeated lookup of the array. I'd declare a local variable Query: TADOQuery and at the start of the method write Query := ADOQueries[Query]. Use Query from then on. That has the benefit that you do not repeat yourself.

emrey Over a year ago

Thank you kind sir. This was what I want. Now, I would like to check that if a particular query is already created or not. something like if (adoqueries[query] is not created) then create...

J... Over a year ago

@user1899291 what you want is if ADOQueries[query] = nil then ADOQueries[query] := TADOQuery.Create(nil);.

David Over a year ago

If you call SetLength on an array, don't forget to later call SetLength(ADOQueries, 0) to free the array memory.

David Heffernan Over a year ago

@DavidM No need, that happens when the array leaves scope

|

ain · Accepted Answer · 2013-05-23 09:36:02Z

3

Another way you can do this is with the FindComponent method, ie assuming the form owns the query components

procedure Tform1.QueryChange(sqltext : String; query : Integer);
var cmp: TComponent;
    Query: TADOQuery;
begin
  cmp := FindComponent('ADOQuery' + IntToStr(query));
  if cmp <> nil then begin
     Query := cmp as TADOQuery;
     Query.Close;
     ...
  end;  
end;

answered May 23, 2013 at 9:36

ain

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3 Comments

Andreas Rejbrand Over a year ago

But this is much less elegant than David's and my solutions. However, since there might be some academical interest in listing different solutions, I will not downvote.

David Heffernan Over a year ago

I can't imagine doing it this way, but I'll upvote all the same. It's a perfectly reasonable answer. Normally you'd not want TADOQuery objects as published components on .dfm files and instead create them programmatically. But for a component that did naturally live in the .dfm file this is a sane way to do it.

Marjan Venema Over a year ago

@DavidHeffernan: I agree that you don't want these components on a form, and would create them in code my self, but in the drag-n-drop way of developing their natural habitat would be a data module and data modules are streamed just like forms are. So, if you are already using data modules, ain's solution would be a good way of doing it.

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