TSQLDBlibraryloader fails @designtime
lazarus / 16-Databases

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mangakissa · 2017-11-04 13:58

I Put TSQLConnector and TSQLDBLibraryloader on form. Set property
libraryname to the path of the clientlibrary. Then I set property
enabled to true.
If I run the application, fpc comes with the error :
Quote'..raised exception class EDatabaseError with the message:
SQLDBLibrayloader1: This operation is not allowed while the database
is loaded.
Why is this happen? property TSQLConnector.connected is still set to
false.

I know it can be fixed at runtime, but my demo requires this option
@designtime.

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LacaK · 2017-11-06 06:39

TSQLDBLibraryLoader message is not related to TSQLConnector.
Probably you have in your code: SQLDBLibrayloader1.Enbled := True; ?
or any other use of SQLDBLibrayloader1 ?

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mangakissa · 2017-11-06 07:45

Yes I did.
So what's the relation to TSQLConnector? I know it tells to the
TSQLConnector where to find the required library. What's the purpose
of the property enabled?

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mangakissa · 2017-11-06 08:38

I looked into the source by property enabled:
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
TSQLDBLibraryLoader.SetEnabled(AValue: Boolean);begin  if
FEnabled=AValue then Exit;  if (csLoading in ComponentState) then   
FEnabled:=AValue  else    If AValue then      LoadLibrary    else    
UnloadLibrary;end;                      Does the clientlibrary has to
be loaded before starting the connection to the database. What is
TSQLconnector doing when the library already loaded?

I couldn't find any code to see what happens if
TSQLConnector.connected is set to true.

There's also a problem with the IDE if the application is haved with
TSQLDBloadlibrary.enabled := true.
When the project will loaded into the IDE, the IDE goes in a loop or
it will fails when loading the TSQLDBloadlibrary.

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molly · 2017-11-06 08:50

Quote from: mangakissa on November 06, 2017, 09:38:15 amI couldn't
find any code to see what happens if TSQLConnector.connected is set to
true.
TSQLConnector inherits from TSQLConnection which in its turn inherits
from TDatabase.

TSQLConnection (re)publishes the property Connected so we go up one
ancestor to see what that does.

Code: [Select]TDataBase: property Connected: Boolean read FConnected
write SetConnected;

So we need to look at TDataBase.SetConnected() but alas, that one is
implemented in (yet another one) its ancestor class TCustomConnection.
so we take a look there:

Code: [Select]procedure TCustomConnection.SetConnected(Value:
boolean);

begin
  If Value<>Connected then
    begin
    If Value then
      begin
      if csReading in ComponentState then
        begin
        FStreamedConnected := true;
        exit;
        end
      else
        begin
        if Assigned(BeforeConnect) then
          BeforeConnect(self);
        DoLoginPrompt;
        DoConnect;
        if Assigned(AfterConnect) then
          AfterConnect(self);
        end;
      end
    else
      begin
      if Assigned(BeforeDisconnect) then
        BeforeDisconnect(self);
      DoDisconnect;
      if Assigned(AfterDisconnect) then
        AfterDisconnect(self);
      end;
    end;
end;

We take a look at DoConnect, which is virtual. We see that its child
TDataBase does override DoConnect and reads:
Code: [Select]procedure TDatabase.DoConnect;
begin
  DoInternalConnect;
  FConnected := True;
end;

So, there it calls DoInternalConnect. DoInternalConnect is overridden
in the child classes. For TSQLConnector that reads:

Quoteprocedure TSQLConnector.DoInternalConnect;

Var
  D : TConnectionDef;

begin
  inherited DoInternalConnect;
  CheckProxy;
  FProxy.CharSet:=Self.CharSet;
  FProxy.DatabaseName:=Self.DatabaseName;
  FProxy.HostName:=Self.HostName;
  FProxy.LogEvents:=Self.LogEvents;
  FProxy.Password:=Self.Password;
  FProxy.Role:=Self.Role;
  FProxy.UserName:=Self.UserName;
  FProxy.FTransaction:=Self.Transaction;
  FProxy.LogEvents:=Self.LogEvents;
  FProxy.OnLog:=Self.OnLog;
  FProxy.Options:=Self.Options;
  D:=GetConnectionDef(ConnectorType);
  D.ApplyParams(Params,FProxy);
  FProxy.Connected:=True;
end;

Note that Inherited DoInternalConnect is executed, so look at its
parent's class implementation of DoInternalConnect as well.

That is, if i understood your question correctly.

edit: added some additional in-between steps

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mangakissa · 2017-11-06 11:21

Part of it Molly.

I tried to understand which relation TSQLDBLibraryloader has to
TSQLConnector (TSQLConnection). If the libraryloader is loading the
clientlibrary, what is TSQLConnector (TSQLConnection) doing with the
loaded library. If this component is not available, TSQLConnector
(TSQLConnection) handles the loading of the client library by itself
(AFAIK). Why is loading my project failing when I use
TSQLDBLibraryloader.enabled := true.
It's nice to know where you can find the procedures of the handled
code, but is not my purpose.
Delphi and Lazarus/FPC are built to build a application in the IDE
without a single code put by user.

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molly · 2017-11-06 12:08

Quote from: mangakissa on November 06, 2017, 12:21:49 pmPart of it
Molly.
Was already afraid you was going to say that :-D

Databases are not my greatest virtue, and usually i set properties
manually at runtime instead of design-time (so double my handicap  )

QuoteI tried to understand which relation TSQLDBLibraryloader has to
TSQLConnector (TSQLConnection).
afaik, none whatsoever other then overriding some default behaviour
(in particular the path and name of the library).

QuoteIf the libraryloader is loading the clientlibrary, what is
TSQLConnector (TSQLConnection) doing with the loaded library.
afaik the libraryloader is responsible for 'correcting' default
behaviour that TSDQLConnection expresses. TSQLConnection and friends
uses a default location (path) and name for the clientlibrary
(.dll/.so) and this might not correspond to your (end-user)situation.
Ergo Library loader let's you customize some (default) settings.

QuoteIf this component is not available, TSQLConnector
(TSQLConnection) handles the loading of the client library by itself
(AFAIK).
afaik as well, yes.

QuoteWhy is loading my project failing when I use
TSQLDBLibraryloader.enabled := true.
No idea atm. The message you showed seem to indicate that the
database/connection has already been opened ("database already
loaded").

QuoteIt's nice to know where you can find the procedures of the
handled code, but is not my purpose.
Indeed it is not, but sometimes knowing the flow of the program is
able to help you understand certain issues/topics. I assumed that is
why you asked the question i quoted and replied to.

QuoteDelphi and Lazarus/FPC are built to build a application in the
IDE without a single code put by user.


Although you as a developer do not have to code anything when visually
creating a design, behind the scenes a lot of code is executed (either
at design-time or at execution time) because of the (visual) changes
that you've made.

All the properties you've changed are stored inside the .lfm file and
when you load your program (either at execution or designtime) these
changes are streamed inside your program and therefor a lot of those
changed properties invoke code (that you probably never knew existed
before).

That is why (under certain circumstances) it is advisable to build
lazarus/components in debug-mode so that you are able to debug the
components source-code at runtime and be able to see what the debugger
has to tell.

Note that afaik using libraryloader requires you to set properties in
a particular order, otherwise things might go amiss (see also here).
Did you follow the rules from that small example ? Also note that
there are some libraryloader examples available in fpc source-tree.

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mangakissa · 2017-11-06 13:59

I'm aware of the wiki part. But AFAIK it's a kind of workaround and
not the solution to the GUI part.
I have to change my script, because it fails @desingtime.
QuoteAlthough you as a developer do not have to code anything when
visually creating a design, behind the scenes a lot of code is
executed (either at design-time or at execution time) because of the
(visual) changes that you've made.
If a compagny gives you a vision to built something without any word
of code typed, it should work. A newbie/beginner doesn't know anything
about the exceptions.

But know this topic is almost offtopic. I shall be carefull for my
answers

I hope that Lacak can explain why TSQLDBLibrary.enabled is not working
as it should.

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molly · 2017-11-06 16:45

Quote from: mangakissa on November 06, 2017, 02:59:36 pmI'm aware of
the wiki part. But AFAIK it's a kind of workaround and not the
solution to the GUI part.
Currently a bit besides the question. To make sure (as you mentioned
it in your first post as well): are you able to 'get rid of' the
exception when you use runtime code ?

QuoteI have to change my script, because it fails @desingtime.
Yes, i am aware. Please don't worry about that 

QuoteA newbie/beginner doesn't know anything about the exceptions.
That is a bit of a contradictio in terminis. The exceptions are (also)
there to help newbies understand errors in a better way, be able to
locate them inside the source so that they can be addressed. I admit,
some exceptions make more sense than others.

Also in this case, the error is clear. The problem lies in figuring
out the 'why' part. I feel that some short example in order to
reproduce the issue would be more helpful.

QuoteI hope that Lacak can explain why TSQLDBLibrary.enabled is not
working as it should.
I'm currently blank as i seem unable to reproduce. So, any help from a
more savvy user would be appreciated.

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LacaK · 2017-11-07 19:28

Quote from: mangakissa on November 06, 2017, 02:59:36 pmI hope that
Lacak can explain why TSQLDBLibrary.enabled is not working as it
should.

I will try.
First how TSQLDBLibraryLoader works was already answered I think.
Simply say TSQLDBLibraryLoader loads appropriate library before any
TSQLConnection tries open connection. When you look into code you will
see that TSQLConnection will load library ONLY if none is already
loaded. So if "somebody" loads library in advance TSQLConnection does
nothing else uses already loaded library.

And why it does not work for you when you set Enabled at design time?
Simply say you found a bug IMO ;-)
It is related to order how published properties are stored/read from
LFM.
When you look into LFM you will see Enabled at first place then
followed by ConnectionType and  LibraryName.
When component is loaded properties are set in order how they are
stored in LFM.
And what is happening in TSQLDBLibraryLoader.SetCType and
TSQLDBLibraryLoader.SetLibraryName ... CheckDisabled is called ...

I will contact author of component to confirm my suspection and will
let you know ...
EDIT: Fixed already in revision: 37570