How to get a object value nested inside document in a collection in MongoDB PHP

Question

I have stored a document set in MongoDB like below where ID is generated automatically through PHP

{
"_id": {
    "$oid": "5ff745237d1b0000860007a6"
},
"user": "5ff741fb7d1b0000860007a4",
"name": "Test",
"slug": "fed73b70d080584c21e0a4353825ef91",
"category": "5fef4a467d1b000086000745",
"images": [{
    "100x128": "test/year/month/image_da4181762396a31ff44f5ddc08ce6186.jpeg",
    "200x256": "test/year/month/image_da4181762396a31ff44f5ddc08ce6186.jpeg",
    "300x385": "test/year/month/image_da4181762396a31ff44f5ddc08ce6186.jpeg",
    "500x642": "test/year/month/image_da4181762396a31ff44f5ddc08ce6186.jpeg"
},
{
    "100x128": "test/year/month/image_da4181762396a31ff44f5ddc08ce6186.jpeg",
    "200x256": "test/year/month/image_da4181762396a31ff44f5ddc08ce6186.jpeg",
    "300x385": "test/year/month/image_da4181762396a31ff44f5ddc08ce6186.jpeg",
    "500x642": "test/year/month/image_da4181762396a31ff44f5ddc08ce6186.jpeg"
}],
}

Now the problem is I want to get value from images object from key 100x128 only from the first array.

I am using the below code to achieve

$productsArray = $collection->aggregate(
    [
        [
            '$match' => [
                                    'user_id' => $user_id
                                ]
        ],
        [ '$unwind' => '$images' ],
        [ '$unwind' => '$images.100x128' ],
        [
            '$project' =>   [
                                        'name' => 1,
                                        'image' => '$images'
                                    ]
        ]
    ]
 );

and I always get an output as below

MongoDB\Model\BSONDocument Object
(
   [storage:ArrayObject:private] => Array
    (
        [_id] => MongoDB\BSON\ObjectId Object
            (
                [oid] => 5ff745357d1b0000860007a7
            )

        [name] => Test 1
        [image] => MongoDB\Model\BSONDocument Object
            (
                [storage:ArrayObject:private] => Array
                    (
                        [100x128] => test/year/month/image_da4181762396a31ff44f5ddc08ce6186.jpeg
                        [200x256] => test/year/month/image_da4181762396a31ff44f5ddc08ce6186.jpeg
                        [300x385] => test/year/month/image_da4181762396a31ff44f5ddc08ce6186.jpeg
                        [500x642] => test/year/month/image_da4181762396a31ff44f5ddc08ce6186.jpeg
                    )

            )

    )

)

I am not sure how to get just that specific value. Where am i going wrong here?

Answer 1

As far as i am getting your question it looks like you would need to understand the mongo concept. So you might get an array representation in UI or in PHP but at the end of day it is object.

Look closely the format that you have posted there is no array but multiple {} in that object just like JS so forget about array concept here.

If my understanding is correct this is what you are looking for

$productsArray = $collection->aggregate(
[
    [
        '$match' => [
                       'user_id' => $user_id
                    ]
    ],
    [ '$unwind' => '$images' ],
    [ '$unwind' => '$images.100x128' ],
    [
        '$project' =>   [
                           'name' => 1,
                           'image' => '$images.100x128'
                        ]
    ]
]

);

Whatever you have googled or used it is correct just you need to add the second unwind value ie $images.100x128 instead of $images in the $project variable.

You can understand this way that $unwind variable uses recursive logic to get output as you want. Like let's say you have an array inside an array first it will get values from internal array then it will come to parent array and then so on. So the last value in $unwind variable should be used.

I am not sure if it will work on multiple objects but as you said you just need the first one. This should do the charm.