Added QueryInterface::emulateExecution()

[klimov-paul]

Q	A
Is bugfix?	no
New feature?	yes
Breaks BC?	yes
Tests pass?	yes
Fixed issues	#6373, #12390

Added QueryInterface::emulateExecution(), which allows preventing of the actual query execution.
This allows to cancel DataProvider preventing search query execution in case search model is invalid:

public function search($params)
    {
        $query = Item::find();

        $dataProvider = new ActiveDataProvider([
            'query' => $query,
        ]);

        $this->load($params);

        if (!$this->validate()) {
            $query->where('0=1');
            $query->emulateExecution(); // No SQL execution will be done
            return $dataProvider;
        }

This also fix unecessary query in case of via() usage. See #12390.

Note: this PR produces minor BC break as it alters yii\db\QueryInterface, however the implementation of new method is present at yii\db\QueryTrait - thus it is less likely to produce a trouble.

[samdark]

I think the name of the method isn't OK since we as users do not clearly separate actual SQL query and getting the result. I propose using another name such as skipQuery() (not sure it's the best one).

[klimov-paul]

Renamed to preventExecution()

[dynasource]

another possibility is 'simulate'

[samdark]

Still looks like a hacky solution but I can't suggest anything better...

[samdark]

Oh! Now I like the naming.

[dynasource]

emulate is even better

[dynasource]

I've reviewed it. I don't know with this solution. It works but it seems to be an overkill for realizing the objective 'DataProvider preventing search query execution'. Aren't there any other solutions out there that are less obtrusive?

[cebe]

Good changes! Need a CHANGELOG and UPGRADE note. Will add them myself. Merging now.

[cebe]

could assert here that the customer table is not empty, otherwise the test would pass without emulateExecution() to work