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aehimself

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aehimself last won the day on December 24 2019

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    Delphi 10.2 Tokyo

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  1. aehimself

    Null value for T

    Is it possible to learn this power? 🙂 To make functions without code? 🙂
  2. aehimself

    Null value for T

    @Dalija Prasnikar Nice, thank you! Exactly what I was looking for 🙂 Just out of curiosity, where it is declared? It says System, but I can not see the implementation. I like to see what I am using 🙂
  3. aehimself

    Null value for T

    Hello all, I'm implementing a custom typed class, e.g.: TMyClass<T> = Class strict protected list: TDictionary<String, T>; public Function Get(Identifier: String): T; End; Function TMyClass<T>.Get(Identifier: String): T; Begin If list.ContainsKey(Identifier) Then Result := list[Identifier] Else Result := ???; End; Question is simple. Is there a default null value for T which I can substitute ??? with? For Strings, it should return '', for numerical values 0, for classes nil and so on. Thanks!
  4. aehimself

    Dynamic creation of SQL queries

    @Anders Melander The good thing is that my prototype consists of exactly the same 4 parts; which makes me believe I'm not drifting too far away from the original goal 🙂 My database structure is not large, consists of 10-ish, 11-ish tables, containing only one circular reference until now. It wouldn't even be impossible to hard code (or generate to source, that is) the shortest possible paths an all possible queries, but I am really against these kind of solutions. I was planning to test this idea on a large database (~1500 tables, multiple circular references, standalone tables, etc.) but I need to extract the fields and connections first. As for the concerns yes - I have them in mind. Especially the crawler. While it works well in my scenario but it's unoptimized and I worry about it's performance on more complex structure. That's something which will turn out on the long run. Scoping is already fully supported. I don't have many fields with the same name but yes, I already saw it as a possible problem source. I also have a theory of a mechanism to analyze and learn the more common requests so future ones can be more close to what the user wanted, but this is strictly a theory until now, and won't even start to work on it until I decide to go with my solution or to purchase a component doing this already. And thank you very much for your post, it was tremendously informative!
  5. aehimself

    Dynamic creation of SQL queries

    I'm not too worried about duplicate file names, as I'm planning to generate the query with TABLENAME.FIELDNAME all the times (thus the mapping) and if the output will show MyField and MyField_1 in the column header... then so be it. As for the IsNull you might be right but not during data display (my database component handles null values as 0, which is perfect in my case) but at WHERE clauses... I recall having an issue on MSSQL not returning correct rows as it handled NULL and 0 (or '', I don't remember exactly) differently. We will see how exactly it will turn out, especially with the "can" you are talking about 🙂 As for the external components I think I will have to gather my strength and finalize my solution. After all it's less than 400 lines (only field mapping and the crawler until now, though) and does not increase the budget. Good news is that I'm either doing this or implementing the requested XML documentation commenting. And I rather code than to do documentation 😄
  6. aehimself

    Dynamic creation of SQL queries

    Good point, but the user is not allowed to write SQL queries at all 🙂 The method I'm working on / looking for is allowing the user to select (enter) field names, maps those to real fields in the database (attempted sql injection will fail at this level as '; DROP TABLE Users; will not map to any field in the database) and based on the mapped fields constructs a SELECT query with proper joins. Maybe I'm not viewing this scenario from all aspects, but I don't see the possibility of a vulnerability here.
  7. aehimself

    What's the best common folder for...

    I also started to use %USERPROFILE% and %APPDATA% as local data storages. If people want to exchange their information, they can export and import; but not necessarily everyone wants to see the same information. Just imagine your application running on a terminal server used by 100+. They will surely want to separate their data.
  8. aehimself

    Dynamic creation of SQL queries

    Hi all, I have an application where I would like the user to be able to "build" what data he wants to see. As I can not expect the user to be an expert in SQL, I need to have an interface where he can just check (or enter) the fields, my program will parse it, generate the necessary SQL query (with proper joins and such), executes it and returns the data. I wrote a small program to "design" the database of the application - it is generating SQL scripts and the code for my custom table-as-an-object implementation - so I have access to all the field and relational information and can output it in any format needed. I already have a prototype which can judge which field in which table to select and a crawler (path finder, basically) which can determine the shortest route between two tables. They seem to be working fine but there's still a lot of work with it (optimizations, beautifying - the usual) which I am soooooo unwilling to do at the moment. So my question is - do I really have to reinvent the wheel? Is there a framework available which can do this for me? And yes, I really hate to redesign working prototypes to production-ready implementations 🙂
  9. aehimself

    Fix for bug in JclShell

    Jokes aside 🙂 A couple of questions popped up in my mind: - Are you sure that "RunAs" is an allowed verb for ShellExecute? https://docs.microsoft.com/en-us/windows/win32/api/shellapi/nf-shellapi-shellexecutea does not seem include it, only https://docs.microsoft.com/en-us/windows/win32/api/shellapi/ns-shellapi-shellexecuteinfoa (JCL's ShellExecAndWait is using the Ex version, so the code itself is good, it's only a misleading comment) - Tip: If the file exists but corrupted (hashes do not match) delete the target file as its useless anyway; but... - Why are you comparing the hashes before and after moving? Did you experience corruption in any occasion? I'm only asking because I personally never met this before. - A little bit more resource friendly way of verification might be to check the exit code of move. I'd say might, because as it never failed on me I don't know what exit code it returns if it corrupted the data. So take this with a grain of salt.
  10. Yes, that was my fear too. Solution is rather easy though - don't use overloads 🙂 I started to experiment and came to the realization that Self can be used in a class function / procedure. It only won't reference an instance, only the class of the calling object - even if it is a child. The below works perfectly: TBase = Class strict protected Function GetAsJSON: String; Virtual; Procedure SetAsJSON(inJSONString: String); Virtual; public Var1: Integer; Class Function New(inJSONString: String): TBase; Class Function New2(inInteger: Integer): TBase; Virtual; Property AsJSON: String Read GetAsJSON Write SetAsJSON; End; TChild = Class(TBase) strict protected Function GetAsJSON: String; Override; Procedure SetAsJSON(inJSONString: String); Override; public Var2: String; Class Function New2(inInteger: Integer; inString: String): TChild; ReIntroduce; End; // Class Function TBase.New(inJSONString: String): TBase; Begin Result := Self.Create; Result.AsJSON := inJSONString; End; Class Function TBase.New2(inInteger: Integer): TBase; Begin Result := Self.Create; Result.Var1 := inInteger; End; Class Function TChild.New2(inInteger: Integer; inString: String): TChild; Begin Result := TChild(inherited New2(inInteger)); Result.Var2 := inString; End; I don't like that there are two "New" methods now, but it feels a lot more clean.
  11. @Attila Kovacs Yep, just tested your theory and it does not work:
  12. Did not pay enough attention when writing the example 🙂 Let me correct myself: TBase = Class public Var1: Integer; Class Function New(inJSONString: String): TBase; Overload; Virtual; Class Function New(inVar1: Integer): TBase; Overload; Virtual; End; TChild = Class(TBase) public Var2: String; Class Function New(inJSONString: String): TChild; ReIntroduce; Overload; Class Function New(inVar1: Integer; inVar2: String): TChild; ReIntroduce; Overload; End;
  13. I think the answer is no but maybe I just did not find the correct way - yet. Imagine the following: TBase = Class public Var1: String; Class Function New(inJSONString: String): TBase; Overload; Virtual; Class Function New(inVar1: String): TBase; Overload; Virtual; End; TChild = Class(TBase) public Var2: Integer; Class Function New(inJSONString: String): TChild; ReIntroduce; Overload; Class Function New(inVar1: String; inVar2: Integer): TChild; ReIntroduce; Overload; End; When I type TChild.New, all four variants are accessible. So the question is: is it possible to completely reintroduce the base classes all overloaded methods, so in the child only the newly declared are accessible?
  14. aehimself

    Best practices for handling a Stalled thread

    Killing a thread is not a good idea in about 99% of the times 🙂 The best case is that it will leak memory and / or abandon TCP connections. Worst case? It can leave corrupted temporary files around, render your application unusable and requiring a restart or even leave the system in an unbootable state (depending what it is doing which gets forcefully interrupted). Sometimes you have no other option though... There are some REALLY good advices there. Maybe you can launch the image processing in a child process - in regards to the host applications state killing a process can be less painful than a killing a thread.
  15. aehimself

    Open Url From Current Line

    There you go, I found it: https://dictionary.cambridge.org/us/dictionary/english/sarcasm I'll try to act like an adult and stop this discussion right here. If you would like to learn more about coding styles, Google is - as always - your friend. In the mean time, please learn how not to get offended when people say their favorite color is not the same as yours.
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