QCombobox Case selection - Pyside2 Index via Sqlite

Question

I have a very simple file where I have a Qcombobox Filter. When you select the filter, I run through a case on the index and output results.

So, on selection I trigger:

self.comboBox.activated.connect(self.handleActivated)

Then,

my handled function is

    def handleActivated(self, index):
        db = QSqlDatabase.addDatabase("QSQLITE")
        db.setDatabaseName("data.db")
        db.open()
        # tableView = QtWidgets.QTableView()

        if index == 0:
            sourceModel = QSqlQueryModel()
            sourceModel.setQuery(
                "SELECT url,size,content_type FROM 'google.com.au'",
                db)
            proxyModel = QSortFilterProxyModel(self)
            proxyModel.setSourceModel(sourceModel)
            self.tableView.setModel(proxyModel)
            self.tableView.setSortingEnabled(True)
        elif index == 1:
            sourceModel = QSqlQueryModel()
            sourceModel.setQuery(
                "SELECT url,size,content_type FROM 'google.com.au' WHERE content_type LIKE '%html%'",
                db)
            proxyModel = QSortFilterProxyModel(self)
            proxyModel.setSourceModel(sourceModel)
            self.tableView.setModel(proxyModel)
            self.tableView.setSortingEnabled(True)
        elif index == 2:
            sourceModel = QSqlQueryModel()
            sourceModel.setQuery(
                "SELECT url,size,content_type FROM 'google.com.au' WHERE content_type LIKE '%javascript%'",
                db)
            proxyModel = QSortFilterProxyModel(self)
            proxyModel.setSourceModel(sourceModel)
            self.tableView.setModel(proxyModel)
            self.tableView.setSortingEnabled(True)

My question is, is this the most efficient way of writing this code ? I have upto 15 filters and this will become really cumbersome in my main file.

Kate · Accepted Answer · 2020-05-18 18:58:19Z

Well you have already identified the problem: repetition. It can be tackled fairly easily. Instead of that if/elif block you can use a (zero-indexed) list that contains the WHERE clause for the query:

    options = [ None, '%html%', '%javascript%']
    query = "SELECT url,size,content_type FROM 'google.com.au'"

    if options[index] is not None:
        query += f" WHERE content_type LIKE '{options[index]}'"

    sourceModel = QSqlQueryModel()
    sourceModel.setQuery(query, db)
    proxyModel = QSortFilterProxyModel(self)
    proxyModel.setSourceModel(sourceModel)
    self.tableView.setModel(proxyModel)
    self.tableView.setSortingEnabled(True)

Only the first option is different: there is no WHERE clause. In the other places the request is always the same, it's only the search pattern that is different.

What I am doing here is simply selective string concatenation. Note: using an F-string for the WHERE clause, requires Python >= 3.6. Usage is not mandatory but if you have a recent version of Python embrace the new features.

Instead of None you could say '' (an empty string). I chose None to signify option #0 is a special case. I am not checking that index is actually in the range 0->2. If you think this could happen, add a if to check.

Wow ! Thank you, that makes much more sense. On running your code I got a small error TypeError: can only concatenate tuple (not “str”) to tuple Error' which I fixed by adding a ()` on the query and it works as expected. — Sam
– Sam, Commented May 19, 2020 at 0:23

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