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determine whether sqlite database is locked

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  • U Offline
    U Offline
    user4592357
    wrote on 22 Aug 2019, 17:23 last edited by
    #1

    i need to determine whether the sqlite database is locked. i found this function which returns that info. but, in order to call this function, i need sqlite3.h and sqlite3.c which doesn't come with qt. so i need to download these files and link them with my project.
    is there a better way to determine whether the database is locked?

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    • S Offline
      S Offline
      SGaist
      Lifetime Qt Champion
      wrote on 22 Aug 2019, 18:53 last edited by
      #2

      Hi,

      From the looks of the documentation, it's rather for when a table is locked. So is it really what you want ?

      Interested in AI ? www.idiap.ch
      Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

      U 1 Reply Last reply 22 Aug 2019, 18:56
      0
      • S SGaist
        22 Aug 2019, 18:53

        Hi,

        From the looks of the documentation, it's rather for when a table is locked. So is it really what you want ?

        U Offline
        U Offline
        user4592357
        wrote on 22 Aug 2019, 18:56 last edited by
        #3

        @sgaist
        yeah i know but that's what i found. i didn't find any other way

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        • F Offline
          F Offline
          fcarney
          wrote on 22 Aug 2019, 19:17 last edited by
          #4

          It is included. Here is how I got to it when playing with sqlite specific functions. You may need to alter some paths if those changed between revisions of Qt:
          https://forum.qt.io/topic/101018/qsqldatabase-sqlite-how-to-load-into-memory-and-save-memory-to-disk/13

          C++ is a perfectly valid school of magic.

          U 1 Reply Last reply 23 Aug 2019, 20:35
          2
          • F fcarney
            22 Aug 2019, 19:17

            It is included. Here is how I got to it when playing with sqlite specific functions. You may need to alter some paths if those changed between revisions of Qt:
            https://forum.qt.io/topic/101018/qsqldatabase-sqlite-how-to-load-into-memory-and-save-memory-to-disk/13

            U Offline
            U Offline
            user4592357
            wrote on 23 Aug 2019, 20:35 last edited by
            #5

            @fcarney
            my application uses a custom built qt (not the one downloaded from the website), and i looked at qtsql, sqldrivers folders, performed a search and didn't find the header file...

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            • F Offline
              F Offline
              fcarney
              wrote on 23 Aug 2019, 20:39 last edited by
              #6

              Did you look in this directory? $$[QT_INSTALL_PREFIX]/../Src/qtbase/src/3rdparty/sqlite

              C++ is a perfectly valid school of magic.

              U 1 Reply Last reply 23 Aug 2019, 20:42
              0
              • F fcarney
                23 Aug 2019, 20:39

                Did you look in this directory? $$[QT_INSTALL_PREFIX]/../Src/qtbase/src/3rdparty/sqlite

                U Offline
                U Offline
                user4592357
                wrote on 23 Aug 2019, 20:42 last edited by user4592357
                #7

                @fcarney
                the directory structure is different
                i have

                qt/
                    include/
                        qtcore,qtgui,...
                    plugins/
                        sqldrivers
                
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                • F Offline
                  F Offline
                  fcarney
                  wrote on 23 Aug 2019, 20:46 last edited by
                  #8

                  I dunno then. If your version supports sqlite I would think it would have to be in there somewhere. The other option is getting a copy of sqlite and using that.

                  C++ is a perfectly valid school of magic.

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                  • M Offline
                    M Offline
                    mrjj
                    Lifetime Qt Champion
                    wrote on 23 Aug 2019, 22:01 last edited by
                    #9

                    Hi
                    But do you really need to know of its locked?
                    You will get an error if you try to perform operations and it is indeed locked.
                    So that case could be treated like any other type of db failure.

                    U 1 Reply Last reply 24 Aug 2019, 04:44
                    1
                    • M mrjj
                      23 Aug 2019, 22:01

                      Hi
                      But do you really need to know of its locked?
                      You will get an error if you try to perform operations and it is indeed locked.
                      So that case could be treated like any other type of db failure.

                      U Offline
                      U Offline
                      user4592357
                      wrote on 24 Aug 2019, 04:44 last edited by
                      #10

                      @mrjj
                      yes i first need to check if the db is locked. because in that case i need to show another dialog, and in all other db access failure cases should be handled differently (just print a message, etc.)

                      M J 2 Replies Last reply 24 Aug 2019, 09:42
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                      • U user4592357
                        24 Aug 2019, 04:44

                        @mrjj
                        yes i first need to check if the db is locked. because in that case i need to show another dialog, and in all other db access failure cases should be handled differently (just print a message, etc.)

                        M Offline
                        M Offline
                        mrjj
                        Lifetime Qt Champion
                        wrote on 24 Aug 2019, 09:42 last edited by
                        #11

                        @user4592357
                        ok. it was worth a shot. :)

                        i would download the source (version wise) of the Qt used to build your
                        custom Qt and take the sqlite files from there to be 100% sure its
                        compatible. or at least check the version used and download that from their site.

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                        • U user4592357
                          24 Aug 2019, 04:44

                          @mrjj
                          yes i first need to check if the db is locked. because in that case i need to show another dialog, and in all other db access failure cases should be handled differently (just print a message, etc.)

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                          JonB
                          wrote on 24 Aug 2019, 10:06 last edited by
                          #12

                          @user4592357

                          @mrjj said:

                          You will get an error if you try to perform operations and it is indeed locked.

                          You said:

                          yes i first need to check if the db is locked. because in that case i need to show another dialog,

                          So since this is proving so difficult, can you not initially try one operation which will raise an error if db is locked, then put up you dialog, and treat any subsequent errors in your standard dialog way?

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                          • U Offline
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                            user4592357
                            wrote on 24 Aug 2019, 10:27 last edited by
                            #13

                            what if the database is locked during the running of the application? in that case i need to perform "is database locked?" before executing each query (even selects). so i guess i need to perform this check before executing each query.

                            J 1 Reply Last reply 24 Aug 2019, 13:05
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                            • U Offline
                              U Offline
                              user4592357
                              wrote on 24 Aug 2019, 12:29 last edited by user4592357
                              #14

                              okay i downloaded the files and built with my project.
                              so i set the db connection timeout to 0:

                              	auto db = QSqlDatabase::database();
                              	db.setDatabaseName(m_sDatabasePath);
                              	db.setConnectOptions("QSQLITE_BUSY_TIMEOUT=0");
                              	if (!db.open())
                              		return false;
                              

                              and then i do this:

                              bool isDatabaseLocked(const QSqlDatabase &db)
                              {
                              	if (auto driver = db.driver())
                              	{
                              		// get driver handler
                              		QVariant v = driver->handle();
                              		if (v.isValid() && qstrcmp(v.typeName(), "sqlite3*") == 0)
                              		{
                              			// v.data() returns a pointer to the handle
                              			auto handle = *static_cast<sqlite3 **>(v.data());
                              			if (handle)
                              			{
                              				std::cout << sqlite3_busy_handler(handle, cb, nullptr) << std::endl;
                              				std::cout << sqlite3_busy_timeout(handle, 0) << std::endl;
                              			}
                              		}
                              	}
                              
                              	return true;
                              }
                              
                              int cb(void *data, int)
                              {
                              	std::cout << "cb" << std::endl;
                              	return 0;
                              }
                              

                              both these functions return 0 (SQLITE_OK) while i'd expect to get 5 (SQLITE_BUSY). and the callback function isn't called either. so what's wrong?

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                              • U user4592357
                                24 Aug 2019, 10:27

                                what if the database is locked during the running of the application? in that case i need to perform "is database locked?" before executing each query (even selects). so i guess i need to perform this check before executing each query.

                                J Online
                                J Online
                                JonB
                                wrote on 24 Aug 2019, 13:05 last edited by
                                #15

                                @user4592357 said in determine whether sqlite database is locked:

                                what if the database is locked during the running of the application? in that case i need to perform "is database locked?" before executing each query (even selects). so i guess i need to perform this check before executing each query.

                                Absolutely not! If it's locked, you'll find out on your genuine call, not an extra check each time!

                                U 1 Reply Last reply 24 Aug 2019, 13:10
                                0
                                • J JonB
                                  24 Aug 2019, 13:05

                                  @user4592357 said in determine whether sqlite database is locked:

                                  what if the database is locked during the running of the application? in that case i need to perform "is database locked?" before executing each query (even selects). so i guess i need to perform this check before executing each query.

                                  Absolutely not! If it's locked, you'll find out on your genuine call, not an extra check each time!

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                                  U Offline
                                  user4592357
                                  wrote on 24 Aug 2019, 13:10 last edited by
                                  #16
                                  This post is deleted!
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                                  • U Offline
                                    U Offline
                                    user4592357
                                    wrote on 28 Aug 2019, 17:46 last edited by
                                    #17

                                    @jonb
                                    yes i know, with lastError(). but what about handling it? should i check if (lastError().startWith("database is locked")) then show dialog else do something else? i don't like this

                                    J 1 Reply Last reply 29 Aug 2019, 07:38
                                    0
                                    • U user4592357
                                      28 Aug 2019, 17:46

                                      @jonb
                                      yes i know, with lastError(). but what about handling it? should i check if (lastError().startWith("database is locked")) then show dialog else do something else? i don't like this

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                                      JonB
                                      wrote on 29 Aug 2019, 07:38 last edited by
                                      #18

                                      @user4592357
                                      If you are are issuing some SQL statement which can only error in your "locked" case then you know where you are. If the "locked" can be returned from any SQL call then it looks like you have little choice but to look at lastError(), since I do not see that Qt returns any information about a SQLite native error number you could examine.

                                      Yes, it's not perfect. Personally I'd still prefer that to having to bring in extra files and compile the driver myself just to get it perfect. What is this locked all about, is your app so critical that you have to get this case perfect, and why are you subject to this issue when loads of other people are using Qt with SQLite without worrying about this?

                                      U 1 Reply Last reply 29 Aug 2019, 08:29
                                      0
                                      • J JonB
                                        29 Aug 2019, 07:38

                                        @user4592357
                                        If you are are issuing some SQL statement which can only error in your "locked" case then you know where you are. If the "locked" can be returned from any SQL call then it looks like you have little choice but to look at lastError(), since I do not see that Qt returns any information about a SQLite native error number you could examine.

                                        Yes, it's not perfect. Personally I'd still prefer that to having to bring in extra files and compile the driver myself just to get it perfect. What is this locked all about, is your app so critical that you have to get this case perfect, and why are you subject to this issue when loads of other people are using Qt with SQLite without worrying about this?

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                                        U Offline
                                        user4592357
                                        wrote on 29 Aug 2019, 08:29 last edited by
                                        #19

                                        @jonb
                                        yes i need to process the locked state of the database because it can potentially be opened from another application as well (in a nutshell, these two apps can talk to each other).

                                        i actually downloaded the files and compiled them. two posts above i show the code which i'm using but it doesn't return anything related to sqlite being busy or locked. is the code actually correct?

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