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List: pykde
Subject: Re: [PyQt] Going multiuser with QSqlRelationalTableModel
From: J Barchan <jnbarchan () gmail ! com>
Date: 2018-03-31 19:37:22
Message-ID: CABz3M_81xpkg3vbTdLGQan8TCPokAF_wCsA_OjkP-04rbJQYAA () mail ! gmail ! com
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On 31 March 2018 at 14:02, Ricardo Araoz <ricaraoz@gmail.com> wrote:
> On 31/03/18 12:37, J Barchan wrote:
>
>
>
> On 30 March 2018 at 16:48, Ricardo Araoz <ricaraoz@gmail.com> wrote:
>
>> Are there any methods for multiuser database programming while working
>> with models and mappers? I mean, something to lock/unlock records and/or
>> tables (not talking about transactions) and something that will tell me
>> when saving if the database records to be updated have been changed since
>> the model read them.
>>
>> TIA
>>
>
> Hi Ricardo,
>
> I am not a PyQt expert person --- just someone using it.
>
> I would say basically "no".
>
> QSqlRelationalTableModel is just a thin layer over QSqlTableModel, and
> that's just QSqlTableQuery/QSqlQuery with some support for putting it in
> a table and allowing you to specify INSERT/DELETE/UPDATE commands. Other
> than that you're really on your own to add your own stuff.
>
> The usual way to handle "multiuser" is to make your DELETE/UPDATE statements
> do *optimistic *updates, i.e. you add a WHERE clause to verify all the
> values in the database are the same as when you read the row in, else
> someone else has changed it and then you error. That's instead of
> *pessimistic* locking, where you lock the row when you read it, which
> doesn't scale. You could implement these yourself.
>
> Otherwise, this isn't a PyQt/Python question, so if you want to discuss in
> detail or see if Qt experts have more to offer than I have you might like
> to join up to https://forum.qt.io/ and come pose your question there.
>
> --
> Kindest,
> Jonathan
>
>
> Hi Jonathan, thanks for your answer. I know I could do it by myself, But
> I'd be missing the automatic behaviour implemented by the
> model/view/delegate schema. I'm now thinking about subclassing the model
> and implementing something in the submit and submitAll methods.
> Cheers
> Ricardo
>
>
But I'd be missing the automatic behaviour implemented by the
> model/view/delegate schema
>
Why would you be missing any of this?
I'm now thinking about subclassing the model and implementing something in
> the submit and submitAll methods
Yes, in case I wasn't clear, of course you should not throw away anything
like the QSqlRelationalTableModel level. You would use that and write
your own sub-classes/super-classes/wrappers to add the functionality you
want on top of what is already there, not replacing it. The approaches I
was suggesting would be in that vein. But my point is you do need to
write the new stuff yourself, unless you can find anything which does this
for you, which I am not aware of.
I have been thinking for a while I'd quite like to add something of a "
QSqlDataSet" class/level to Qt to encapsulate the relationships between
multiple QSqlRelationalTableModels, and so much more. Do you think that
would be a good idea?
--
Kindest,
Jonathan
[Attachment #5 (text/html)]
<div dir="ltr"><div class="gmail_default" \
style="font-family:tahoma,sans-serif"></div><div \
class="gmail_extra"><br></div><div class="gmail_quote">On 31 March 2018 at 14:02, \
Ricardo Araoz <span dir="ltr"><<a href="mailto:ricaraoz@gmail.com" \
target="_blank">ricaraoz@gmail.com</a>></span> wrote:<br><blockquote \
class="gmail_quote" style="margin:0px 0px 0px \
0.8ex;padding-left:1ex;border-left-color:rgb(204,204,204);border-left-width:1px;border-left-style:solid">
<div bgcolor="#FFFFFF"><span>
On 31/03/18 12:37, J Barchan wrote:<br>
</span><blockquote type="cite">
<div dir="ltr">
<div style="font-family:tahoma,sans-serif"></div>
<div class="gmail_extra"><span><br>
<div class="gmail_quote">On 30 March 2018 at 16:48, Ricardo
Araoz <span dir="ltr"><<a href="mailto:ricaraoz@gmail.com" \
target="_blank">ricaraoz@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px \
0.8ex;padding-left:1ex;border-left-color:rgb(204,204,204);border-left-width:1px;border-left-style:solid">Are
there any methods for multiuser database programming while
working with models and mappers? I mean, something to
lock/unlock records and/or tables (not talking about
transactions) and something that will tell me when saving
if the database records to be updated have been changed
since the model read them.<br>
<br>
TIA<br>
</blockquote>
</div>
<br>
</span><span><div style="font-family:tahoma,sans-serif">Hi \
Ricardo,</div> <div style="font-family:tahoma,sans-serif"><br>
</div>
<div style="font-family:tahoma,sans-serif">I am not a PyQt expert
person --- just someone using it.</div>
<div style="font-family:tahoma,sans-serif"><br>
</div>
<div style="font-family:tahoma,sans-serif">I would say basically
"no". <div class="gmail_default" \
style="font-family:tahoma,sans-serif;display:inline"></div><font \
face="monospace,monospace">QSqlRelationalTableModel
</font><span class="gmail-m_-6466530370896208889gmail-J-J5-Ji" \
id="gmail-m_-6466530370896208889gmail-:a9"></span>is
just a thin layer over <font \
face="monospace,monospace">QSqlTableModel</font>,
and that's just <font \
face="monospace,monospace">QSqlTableQuery</font>/<font \
face="monospace,monospace">QSqlQuery </font>with some support for putting it in a \
table and allowing you to specify <font \
face="monospace,monospace">INSERT</font>/<font \
face="monospace,monospace">DELETE</font>/<font face="monospace,monospace">UPDATE \
</font>commands. Other
than that you're really on your own to add your own stuff.</div>
<div style="font-family:tahoma,sans-serif"><br>
</div>
<div style="font-family:tahoma,sans-serif">The usual way to
handle "multiuser" is to make your <font face="Courier \
New">DELETE</font>/<font face="monospace,monospace">UPDATE </font><span \
class="gmail-m_-6466530370896208889gmail-J-J5-Ji" \
id="gmail-m_-6466530370896208889gmail-:a9">statements do \
<em>optimistic
</em>updates, i.e. you add a <font \
face="monospace,monospace">WHERE</font> clause to verify all the values in the \
database are the same as when you read the row in, else someone else has changed it \
and then you error. That's instead of <em>pessimistic</em>
locking, where you lock the row when you read it, which
doesn't scale. You could implement these yourself.</span></div>
<div style="font-family:tahoma,sans-serif"><span \
class="gmail-m_-6466530370896208889gmail-J-J5-Ji"><br> </span></div>
<div style="font-family:tahoma,sans-serif"><span \
class="gmail-m_-6466530370896208889gmail-J-J5-Ji">Otherwise, this isn't a \
PyQt/Python question, so if you want to discuss in detail or see if Qt
experts have more to offer than I have you might like to
join up to <a href="https://forum.qt.io/" \
target="_blank">https://forum.qt.io/</a> and come pose your question \
there.</span></div>
<div style="font-family:tahoma,sans-serif"><span \
class="gmail-m_-6466530370896208889gmail-J-J5-Ji"><br>
-- <br>
</span></div>
<div class="gmail-m_-6466530370896208889gmail_signature">
<div dir="ltr">
<div>
<div dir="ltr">
<div><span \
style="font-family:tahoma,sans-serif">Kindest,</span></div>
<div><span \
style="font-family:tahoma,sans-serif">Jonathan</span></div> </div>
</div>
</div>
</div>
</span></div>
</div>
</blockquote>
<br>
Hi Jonathan, thanks for your answer. I know I could do it by myself,
But I'd be missing the automatic behaviour implemented by the
model/view/delegate schema. I'm now thinking about subclassing the
model and implementing something in the submit and submitAll
methods.<br>
Cheers<span class="gmail-HOEnZb"><font color="#888888"><br>
Ricardo<br>
<br>
</font></span></div>
</blockquote></div><div class="gmail_extra"><br></div><div \
class="gmail_extra"><br></div><div class="gmail_extra"><br></div><blockquote \
class="gmail_quote" style="margin:0px 0px 0px \
0.8ex;padding-left:1ex;border-left-color:rgb(204,204,204);border-left-width:1px;border-left-style:solid"><div \
class="gmail_default" style="font-family:tahoma,sans-serif;display:inline"><font \
face="Arial">But I'd be missing the automatic behaviour implemented by the \
model/view/delegate schema</font></div></blockquote><div class="gmail_default" \
style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" \
style="font-family:tahoma,sans-serif"></div><div class="gmail_default" \
style="font-family:tahoma,sans-serif">Why would you be missing any of \
this?</div><div class="gmail_default" \
style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" \
style="font-family:tahoma,sans-serif"><br></div><blockquote class="gmail_quote" \
style="margin:0px 0px 0px \
0.8ex;padding-left:1ex;border-left-color:rgb(204,204,204);border-left-width:1px;border-left-style:solid">I'm \
now thinking about subclassing the model and implementing something in the submit \
and submitAll methods</blockquote><div class="gmail_default" \
style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" \
style="font-family:tahoma,sans-serif">Yes, in case I wasn't clear, of course you \
should not throw away anything like the <font \
face="monospace,monospace">QSqlRelationalTableModel</font> level. You would use \
that and write your own sub-classes/super-classes/wrappers to add the functionality \
you want on top of what is already there, not replacing it. The approaches I was \
suggesting would be in that vein. But my point is you do need to write the new \
stuff yourself, unless you can find anything which does this for you, which I am not \
aware of.</div><div class="gmail_default" \
style="font-family:tahoma,sans-serif"><br></div><div class="gmail_default" \
style="font-family:tahoma,sans-serif">I have been thinking for a while I'd \
quite like to add something of a "<font \
face="monospace,monospace">QSqlDataSet</font>" class/level to Qt to encapsulate \
the relationships between multiple <font \
face="monospace,monospace">QSqlRelationalTableModel</font>s, and so much more. Do \
you think that would be a good idea?<br clear="all"><br>-- <br></div><div \
class="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><span \
style="font-family:tahoma,sans-serif">Kindest,</span></div><div><span \
style="font-family:tahoma,sans-serif">Jonathan</span></div></div></div></div></div><div \
class="gmail_extra"> </div></div>
[Attachment #6 (text/plain)]
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