Newbie problem with TDictionary
lazarus / 67-Windows

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phunkz · 2024-11-02 22:40

Hi there,

using fpc 3.2.2 in ide lazarus 3.4 and today updated to 3.6 (no change
in behaviour) under win 10 in a Virtualbox VM with enough free ram

I desperately want to create a global Database object which holds data
in a key-value-store using a Tdictionary.
Later on i want to use a real database for persistent storage. but for
now a TDict should do the job.
Now i have created a unit which defines a class TDatabase with a
private KeyValueDict: TDictionary , its methods constructor
create/get/store/destructor destroy/and  instantiates a variable
GlobalDatastore

But after "create" it seems, while stepping with the debugger, that
the destructor is directly called afterwards which i dont understand.
is anything wrong with the method "create"?
Any access via "get" to KeyValueDict throws a read memory error.
Compiling is fine but lots of warnings making me nervous.
Ive used the some AIs and the search function in this forum but could
not find a solution
Ive added C:\lazarus\fpc\3.2.2\source\packages\rtl-generics\src to the
path. Without this stepping into TDictionary was not possible.
Any Ideas?
I'm a total newbie to pascal but not for  programming in other
languages so its possible that ive done some pretty dumb mistakes.
Many thanks in advance.

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
TT_database;// shared object {$mode Delphi}  {$H+} interface uses 
Classes, SysUtils, Generics.Collections, Variants; type  TDataBase =
class  private    KeyValueDict: TDictionary<string, Variant>;  public 
  constructor Create;    destructor Destroy; override;    procedure
Store(const Key: string; const Value: Variant);    function Get(const
Key: string): Variant;  end; var  GlobalDatastore:
TDataBase; implementation { TDataBase } constructor
TDataBase.Create;begin  KeyValueDict := TDictionary<string,
Variant>.Create;end; destructor TDataBase.Destroy;begin 
KeyValueDict.Free;  inherited;end; procedure TDataBase.Store(const
Key: string; const Value: Variant);begin  KeyValueDict.Add(Key,
Value);end; function TDataBase.Get(const Key: string): Variant;begin 
if KeyValueDict.ContainsKey(Key) then    Result := KeyValueDict[Key] 
else    Result := Null; // Verwende Null anstelle eines leeren Strings
für Variantend; initialization  GlobalDatastore :=
TDataBase.Create; finalization  GlobalDatastore.Destroy; end.

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silvercoder70 · 2024-11-03 01:59

Hi,

I have used your code exactly as is and it actually worked for me and
behind a button put code ...

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.Button1Click(Sender: TObject);var  s: string;begin 
GlobalDatastore.Store('a', '1');   s := GlobalDatastore.Get('a'); 
showMessage(s);end;     
Please keep in mind I am using the 4.0RC1 and FPC 3.2.2.

As a side-note I did set breakpoints in all of your functions/methods
as well. What versions are you using?

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Thaddy · 2024-11-03 07:04

Your code is a bit, well, over the top for what you actually mean.
Maybe you can do it like this:Code: Pascal
 [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
mydatab;{$mode delphi}interfaceuses  Generics.Collections; // that is
all you need type  TYourDatabase = TDictionary<string, Variant>; var 
GlobalDatastore: TYourDatabase; implementation initialization 
GlobalDatastore := TYourDatabase.Create; finalization 
GlobalDatastore.Free; end.
I would not call your data store TDatabase, since that is an existing
and often used class.
I also would not use store and get if all they do is calling add and
retrieve, so I removed that.

Above unit is tested and working.

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phunkz · 2024-11-04 01:40

Thanks to both,

working on your tipps, especially on the naming conventions,
i found the error, really dumb as previously announced...

I had an identically named local variable in the calling unit...