multithreading - How can I query asynchronously via a QSqlQueryModel? -


i wish query sql database via qsqlquerymodel (pyqqt 5/qt 5.2) asynchronously, gui doesn't block. how can accomplished? maybe through multithreading? please provide code of how this. if using qsqlquerymodel asynchronously isn't practical, feel free provide alternatives (should usable qtableview though).

my (synchronous) code looks shown beneath. main script bin/app.py loads gui/__init__.py , executes main method. in turn uses gui.models.table load data database. problem gui.models.table queries database synchronously , locks gui in meantime.

bin/app.py:

import os.path import sys  sys.path.insert(0, os.path.abspath(os.path.join(     os.path.dirname(__file__), "..")))  import gui   if __name__ == "__main__":     gui.main()

gui/__init__.py:

import sys import os.path pyqt5 import uic pyqt5 import qtcore, qtwidgets  gui import models   class mainwindow(qtwidgets.qmainwindow):     def __init__(self):         super(mainwindow, self).__init__()         uic.loadui(os.path.join(os.path.dirname(__file__), 'app.ui'), self)         self.tableview.setmodel(models.table(self))   def main():     app = qtwidgets.qapplication(sys.argv)     w = mainwindow()     w.show()     app.exec_()

gui/models.py:

import os.path pyqt5.qtcore import * pyqt5.qtsql import *   class table(qsqlquerymodel):     def __init__(self, parent=none):         super(table, self).__init__(parent)          pth = os.path.abspath(os.path.join(os.path.dirname(__file__), "..",                                            "test.sqlite"))         db = qsqldatabase.adddatabase("qsqlite")         db.setdatabasename(pth)         if not db.open():             raise exception("couldn't open database '{}'".format(pth))         try:             self.setquery("select * test")         finally:             db.close()

unfortunately, typical database driver qt (or else, really) uses synchronous. qt views unfortunately don't know how deal models in foreign threads.

the solution requires shim proxy model, subclassing qidentityproxymodel. first step in implementation shim of source model's method calls blocking qmetaobject::invokemethod calls. needed correct, if not asynchronous yet. it' expose safe interface model lives in thread.

the next step provide asynchronous veneer on of functionality. suppose want make data method asynchronous. is:

  1. for each role, have cache of variant values keyed model index.

  2. on datachanged signal source model, cache values changed, across roles. data call needs queued in model's thread - more on later.

  3. in data, if there's cache hit, return it. otherwise return null variant , queue data call in model's thread.

your proxy should have private method called cachedata called queued calls. in answer, i've detailed how queue functor calls in thread. leveraging that, data call queuing method can like:

void threadsafeproxymodel::queuedatacall(const qmodelindex & index, int role) {   int row = index.row();   int column = index.column();   void * data = index.internalpointer();   postmetacall(sourcemodel()->thread(), [this, row, column, data, role]{     qvariant data = sourcemodel()->data(createindex(row, column, data), role);     qmetaobject::invoke(this, "cachedata",                          q_arg(qvariant, data), q_arg(int, role),                         q_arg(int, row), q_arg(int, column), q_arg(void*, data));   }); }

this sketch. it'd involved, doable, , still maintaining semantics of real model.


Comments

Post a Comment

Popular posts from this blog

basic authentication with http post params android -

i doing basic authentication passing username , password , using basicnamevaluepair sending post params response service. my method: public stringbuilder callservicehttppost(string username, string password, string type) { // create new httpclient , post header httpclient httpclient = new defaulthttpclient(); httppost httppost = new httppost(webservice + type); httpresponse response = null; stringbuilder total = new stringbuilder(); try { url url = new url(webservice + type); /*string base64encodedcredentials = base64.encodetostring((username + ":" + password).getbytes(), base64.url_safe | base64.no_wrap);*/ string base64encodedcredentials = "basic " + base64.encodetostring( (username + ":" + password).getbytes(), base64.no_wrap); httppost.setheader("auth...
Read more

vb.net - Virtual Keyboard commands -

i wondering difference between virtual these keyboard commands is: keyeventf_extendedkey , keyeventf_keyup is. everywhere have looked gives me description based off integers , not want know each of them does. you've tagged question vb.net, these have nothing @ vb.net. they're constants defined in windows header files, use win32 api functions. as far difference, can't tell looking @ values. individual values not particularly important, that's why named identifiers used. what's important used , documentation functions tells mean. the first one, keyeventf_extendedkey , used keybdinput structure (which used along e.g. sendinput function) pass information synthesized keyboard input. if flag used, means scan code should interpreted extended key. technically, means scan code preceded prefix byte value 224 (&he0 in hexadecimal notation). the second one, keyeventf_keyup , 1 of flags available use structure. means key being released (going up)...
Read more

How to get multiresult with multicondition in Sql Server -

i need solve this. hopefully can giving me advices. for sample, i've got data : proclib.march 1 first 10 rows flight date depart orig dest miles boarded capacity ----------------------------------------------------------------- 114 01mar94 7:10 lga lax 2475 172 210 202 01mar94 10:43 lga ord 740 151 210 219 01mar94 9:31 lga lon 3442 198 250 622 01mar94 12:19 lga fra 3857 207 250 132 01mar94 15:35 lga yyz 366 115 178 271 01mar94 13:17 lga par 3635 138 250 302 01mar94 20:22 lga 229 105 180 114 02mar94 7:10 lga lax 2475 119 210 202 02mar94 10:43 lga ord 740 120 210 219 02mar94 9:31 lga lon 344...
Read more