Re: [Lazarus] Treeview Question
On 6/30/20 1:10 AM, Martin via lazarus wrote: Hi, I'm porting an application I started (but never finished) in Pyside to Lazarus. This question is only about cosmetics as Treeview works as I want it to. In Pyside I could set a space between nodes by setting the node text as "" and disabling that node so it never gets selection, e.g. self.tvSpace001 = QTreeWidgetItem(self.leftTreeWidget) self.tvSpace001.setText(0, "") self.tvSpace001.setDisabled(True) In Lazarus there seems to be no disabled property for nodes, so when transversing a node with text "" with the keyboard, it will move onto that empty node but not highlight it, when I would prefer it instead moved onto the next or previous node and highlight it. I could write a workaround, storing the last node index, working out if the user has moved up or down, checking if the text is "" and highlighting the previous or next node as required, BUT I just wondered if anyone has a more simple, more elegant solution please? It's only to show visual definition between groups of parents and childs and doesn't actually affect how the application works. Lazarus uses it's own implementation of TTreeView, so you have to create your own LCL wrapper for QTreeWidget. zeljko -- ___ lazarus mailing list lazarus@lists.lazarus-ide.org https://lists.lazarus-ide.org/listinfo/lazarus
Re: [Lazarus] Treeview Question
Thank you. I didn't particularly want to use QT in Lazarus but Pyside is QT only. I'll get my application up and working first I think and then maybe have a look at the treeview source for cosmetic tweaks. Writing my own wrapper for a QT widget set is beyond my capabilities but thank you anyway. Best regards, Martin On 30 June 2020 08:09:39 zeljko wrote: On 6/30/20 1:10 AM, Martin via lazarus wrote: Hi, I'm porting an application I started (but never finished) in Pyside to Lazarus. This question is only about cosmetics as Treeview works as I want it to. In Pyside I could set a space between nodes by setting the node text as "" and disabling that node so it never gets selection, e.g. self.tvSpace001 = QTreeWidgetItem(self.leftTreeWidget) self.tvSpace001.setText(0, "") self.tvSpace001.setDisabled(True) In Lazarus there seems to be no disabled property for nodes, so when transversing a node with text "" with the keyboard, it will move onto that empty node but not highlight it, when I would prefer it instead moved onto the next or previous node and highlight it. I could write a workaround, storing the last node index, working out if the user has moved up or down, checking if the text is "" and highlighting the previous or next node as required, BUT I just wondered if anyone has a more simple, more elegant solution please? It's only to show visual definition between groups of parents and childs and doesn't actually affect how the application works. Lazarus uses it's own implementation of TTreeView, so you have to create your own LCL wrapper for QTreeWidget. zeljko -- ___ lazarus mailing list lazarus@lists.lazarus-ide.org https://lists.lazarus-ide.org/listinfo/lazarus
Re: [Lazarus] SQLdb: Pseudo Transaction?
Am 30.06.2020 um 01:55 schrieb R.Smith via lazarus: Just remove all the transaction bits of your code, and it should work fine. Ryan, your answer helps a lot; thank you. Another (maybe stupid) question: What exactly is the purpose of a 'transaction'? Do I need it for each SQL statement to be executed? Thanx -- Joe -- ___ lazarus mailing list lazarus@lists.lazarus-ide.org https://lists.lazarus-ide.org/listinfo/lazarus
Re: [Lazarus] Treeview Question
On Tue, Jun 30, 2020 at 2:10 AM Martin via lazarus wrote: > In Lazarus there seems to be no disabled property for nodes, ... It could be implemented in TreeNode. However property "Enabled" instead of "Disabled" would be more consistent with other controls. Juha -- ___ lazarus mailing list lazarus@lists.lazarus-ide.org https://lists.lazarus-ide.org/listinfo/lazarus
Re: [Lazarus] Treeview Question
On Tue, 30 Jun 2020 11:20:58 +0300 Juha Manninen via lazarus wrote: > On Tue, Jun 30, 2020 at 2:10 AM Martin via lazarus > wrote: > > In Lazarus there seems to be no disabled property for nodes, ... > > It could be implemented in TreeNode. > However property "Enabled" instead of "Disabled" would be more > consistent with other controls. Or you can write a descendant of TTreeView with your descendant of TTreeNode. Mattias -- ___ lazarus mailing list lazarus@lists.lazarus-ide.org https://lists.lazarus-ide.org/listinfo/lazarus
Re: [Lazarus] SQLdb: Pseudo Transaction?
Ryan, your answer helps a lot; thank you. Another (maybe stupid) question: What exactly is the purpose of a 'transaction'? Do I need it for each SQL statement to be executed? That's an excellent question in fact - lots of confusion out there. Two main reasons, which I will quickly show - 1 - ACID guarantees (especially Isolation and Consistency, the others [Atomicity and Durability] you get anyway), and 2 - Speed. (https://en.wikipedia.org/wiki/ACID) In most DB engines (SQLite definitely) most executed commands gets their own little wrapped transaction if you did not start one explicitly - just to make the nuts and bolts of the engine function correctly. This might be a "lesser" form of transaction, but it has to at a minimum prepare the table, lock tables/rows/whatever, do the reading/writing, and then release those locks. This also means that if you issue four commands, let's use an example (based loosely on a contacts-list table), say you execute these three in order: SELECT MAX(ID) FROM contacts; (The result of the previous statement is put into a variable, say: X) INSERT INTO contacts(ID, FirstName, LastName, TimeAdded, ) VALUES (X+1, 'Joe', 'Soap', Now, ...); INSERT INTO contacts(ID, FirstName, LastName, TimeAdded, ) VALUES (X+2, 'Joe', 'Jones', Now, ...); INSERT INTO contacts(ID, FirstName, LastName, TimeAdded, ) VALUES (X+3, 'Joe', 'Smith', Now, ...); Now inside the DB Engine, it is wrapped in pseudo-code like this (Obviously there is more going on, but I'm just mentioning the interesting bits to our example): tt = Start_Transaction; qq = prepare query( SELECT MAX(ID) FROM contacts; ) : if (qq is READ Query) obtain_read_lock(tt, qq); // Executed ELSE obtain_write_lock(tt, qq);// Skipped run_query(qq); output_results; drop_locks(tt, qq); release_prepared_resources(qq); IF ERRORS > 0 roll_back(tt); ELSE commit(tt); release_transaction(tt); tt = Start_Transaction; qq = prepare query( INSERT INTO contacts(ID, FirstName, LastName, TimeAdded, ...) VALUES (X+1, 'Joe', 'Soap', Now, ...); ) : if (qq is READ Query) obtain_read_lock(tt, qq);// Skipped ELSE obtain_write_lock(tt, qq); // Executed run_query(qq); output_results; drop_locks(tt, qq); release_prepared_resources(qq); IF ERRORS > 0 roll_back(tt); ELSE commit(tt); release_transaction(tt); tt = Start_Transaction; qq = prepare query(INSERT INTO contacts(ID, FirstName, LastName, TimeAdded, ...) VALUES (X+2, 'Joe', 'Jones', Now, ...); ) : if (qq is READ Query) obtain_read_lock(tt, qq); // Skipped ELSE obtain_write_lock(tt, qq); // Executed run_query(qq); output_results; drop_locks(tt, qq); release_prepared_resources(qq); IF ERRORS > 0 roll_back(tt); ELSE commit(tt); release_transaction(tt); tt = Start_Transaction; qq = prepare query(INSERT INTO contacts(ID, FirstName, LastName, TimeAdded, ...) VALUES (X+3, 'Joe', 'Smith', Now, ...); ) : if (qq is READ Query) obtain_read_lock(tt, qq); // Skipped ELSE obtain_write_lock(tt, qq); // Executed run_query(qq); output_results; drop_locks(tt, qq); release_prepared_resources(qq); IF ERRORS > 0 roll_back(tt); ELSE commit(tt); release_transaction(tt); The "output_results;" command might be a no-op for INSERT queries, though some DBs do return values. Now note some things: Towards Point 1 above: If someone else also were trying to insert to this database at the same time, they might get an X that is in-between your inserts, and indeed insert values in between. This is called a concurrancy problem and is fixed by the "isolation" in an ACID transaction. (I know that behaviour can well be fixed by declaring the ID column with AUTO_INCREMENT, but let's imagine it wasn't in this example, you may well have other columns that must be Unique). Note also that the inserted values for "Now()" would be slightly different every time since it's just a littlebit later when the next INSERT happens. Inside a transaction, the TimeAdded values will all be the same. Basically, while the transaction is in progress, and for the duration of it, no other connection to the same database can mess with those values, plus those values will remain consistent for the duration of the transaction. This is a very important property to many people. There are a few other considerations to get technical with, like Serializability modes etc, allowing Dirty-reads, Read-uncommitted data (they don't fall in the scope of this discussion, but you can look them up if interested) - i'll only say here that not everyone wants their transactions to be closed off completely so Database Engines have switches/ways
Re: [Lazarus] SQLdb: Pseudo Transaction?
Hi, Ryan, I followed your advice and removed XTransaction and all references to it from TestButtonClick. But now I get an exception with the message "Transaction not set". Any hint? Regards -- Joe -- ___ lazarus mailing list lazarus@lists.lazarus-ide.org https://lists.lazarus-ide.org/listinfo/lazarus
Re: [Lazarus] SQLdb: Pseudo Transaction?
On Tue, 30 Jun 2020, Special via lazarus wrote: Hi, Ryan, I followed your advice and removed XTransaction and all references to it from TestButtonClick. But now I get an exception with the message "Transaction not set". Any hint? With SQLDB you always need a transaction component. What you can do is set stoUseImplicit in the Transaction.Options: https://www.freepascal.org/docs-html/current/fcl/sqldb/tsqltransaction.options.html In that case the implicit transaction handling of the DB engine (SQLite in this case) will be used, no explicit transaction statements will be emitted. Michael. -- ___ lazarus mailing list lazarus@lists.lazarus-ide.org https://lists.lazarus-ide.org/listinfo/lazarus
Re: [Lazarus] SQLdb: Pseudo Transaction?
On 2020/06/30 22:52, Special via lazarus wrote: Hi, Ryan, I followed your advice and removed XTransaction and all references to it from TestButtonClick. But now I get an exception with the message "Transaction not set". Any hint? Regards -- Joe I'm sorry, the previous problem was SQLite-related, which I'm initimately familiar with, but this one seems to be a Lazarus DB component requirement which I'm not so much familiar with, but probably has an easy solution someone here might know about. The question becomes: How to execute a query, without a transaction being set, using SQLdb in Lazarus? PS: In case you wonder, we're in the process of porting an existing SQLite management tool (https://sqlitespeed.com) to open-source multi-platform from Delphi to FPC and Lazarus - It's been quite a job but going well, and I love the Lazarus/FPC environment more and more, will never go back to Delphi/VS. I do however access SQLite through the API rather than the SQLdb provided components, which is why I can tell you lots about SQL and SQLite but not so much about SQLdb... So apologies for that - hope someone can answer this with some more pertinent knowledge. -- ___ lazarus mailing list lazarus@lists.lazarus-ide.org https://lists.lazarus-ide.org/listinfo/lazarus
