Apply primary readPreference to certain commands

[alcaeus]

Fixes #181.

[jmikola]

Is this merely guarding against the assumption below that there is at least one key in the command document?

Is the command document always a PHP array here, or might the user have supplied a stdClass? ext-mongo uses PHP's Hash API to access keys and would work with either.

[alcaeus]

Good point about the object - I'll have to check that. I've only used arrays, but it's worth adding a test against objects as well 👍

[alcaeus]

I took a look and I typehinted array in the constructor of MongoCommandCursor, although I might have to loosen that up depending on what ext-mongo does. For now, the check against an empty array works.

[jmikola]

If we're mimicking ext-mongo exactly (here), this should only return true when out is a PHP array and inline exists as an array key.

For what it's worth, both of ext-mongo's checks are flawed. Ideally, out could be either an array or object and inline should probably have a true value (in the BSON sense, not PHP -- although that really depends on the server's mapReduce handling).

[alcaeus]

I noticed the original check was flawed. Isn't omitting out the same as providing out with inline set? In that case, the absence of out would indicate the command supports readPreference since it's not required to run on a primary server to write results to a new collection.

That's why the check was written this way - when out isn't set or when inline is set (and ideally set to true, I agree on that) the command supports a readPreference. In all other cases we need to enforce a primary readPreference on the command.

[jmikola]

Isn't omitting out the same as providing out with inline set?

Omitting out results in the following server error on 3.4: "out has to be a string or an object".

Moreover, the server doesn't seem to care about the value of inline, so even { inline: false } is enough to produce an inline result.

So, if you'd like to mimic ext-mongo exactly, this can be changed to:

return (isset($this->command['out']) &&
        is_array($this->command['out']) &&
        array_key_exists('inline', $this->command['out']));

And if you'd like a robust approach:

$out = isset($this->command['out']) ? $this->command['out'] : null;

return (is_array($out) || is_object($out)) && array_key_exists('inline', (array) $out);

[alcaeus]

I've updated the code to mimic ext-mongo, even if it may be flawed. Thanks for your help!