Object storage and retrieval in PHP part 2 – MongoDb

In part one, I talked about how to save and retrieve a PHP object instance using JSON files, and in this post I talk about the same operation using mongoDb, and some gotchas.

I’ve only tried this in very limited circumstances, mainly to see how feasible it would be to make eatStatic seamlessly switch between json files and mongo – I naively thought that you would just throw a json file at mongo and have it store it for you, but the examples i’ve found takes the php object and converts to JSON magically, and also passes back a PHP object instance rather than raw JSON.

This post doesn’t cover installing mongo, I skipped between several different examples/ tutorials before I got it working, so can’t remember exactly how I did it in the end. Once installed though you can connect to it from PHP like this:-


$m = new Mongo(); // connect
$db = $m->cms; // select a database


For comparison purposes we’ll create a simple case study object like in Part 1:-


class case_study {
var $id;
var $title;
var $body_text;
var $skills = array();
}

$case_study = new case_study;

$case_study->id = 'my/case_study';
$case_study->title = 'My case study';
$case_study->body_text = 'Some text for the case study';
$case_study->skills['css'] = 'CSS';
$case_study->skills['sitebuild'] = 'Site Build';


which gives us:-


case_study Object
(
[id] => my/case_study
[title] => My case study
[body_text] => Some text for the case study
[skills] => Array
(
[css] => CSS
[sitebuild] => Site Build
)

)


To store this in mongo db, we simply specify a collection to use (“collection” is analogous to table in a relational database, but you can create them on demand, and don’t have to specify a schema) and them insert our object:-


$case_studies = $db->case_studies;
$case_studies->insert($case_study);


To get it back we use:-


$case_study = $case_studies->findOne(array('id' => 'my/case_study'));


Passing this to print_r() gives us:-


Array
(
[_id] => MongoId Object
(
[$id] => 4e6de720d2db288b0c000000
)

[id] => my/case_study
[title] => My case study
[body_text] => Some text for the case study
[skills] => Array
(
[css] => CSS
[sitebuild] => Site Build
)

)


Note a couple of things:-

• It has given us back an Array, instead of an object
• It has inserted it’s own unique ID [_id]

We don’t need to worry about the extra ID, as we’ll be using our own for lookups, so it can be ignored. To convert the array to an object, simply do:-


$case_study = (object) $case_study;


Which takes us back to:-


stdClass Object
(
[_id] => MongoId Object
(
[$id] => 4e6de720d2db288b0c000000
)

[id] => my/case_study
[title] => My case study
[body_text] => Some text for the case study
[skills] => Array
(
[css] => CSS
[sitebuild] => Site Build
)

)