How can I update an Array of objects instead of object of objects?

[bobbylinux]

Hi, I'm trying to update a tree structure inside a document.
First of all I retrieve data from database with this expression:

$format = Format::findOrFail($formatId);

then I pass my structure called "sectionsOrder" into a dedicated variable and try to remove a specific element with a function.

$sectionsOrder = $format->sectionsOrder;
$sectionsOrder = $this->findAndRemoveSectionInSectionsOrder($sectionsOrder, $sectionId);
$format->sectionsOrder = $sectionsOrder;
$format->save();

The result of this is an ARRAY of Arrays. and finally I save all. Result I've found in my database "sectionsOrder" field an object of objects...

"sectionsOrder" : {
                "1" : {
                        "id" : "5fb09b5f594f0000350074d7"
                },
                "2" : {
                        "id" : "5fb09b5f594f0000350074d8"
                },
                "3" : {
                        "id" : "5fb09b5f594f0000350074d9"
                },
                "4" : {
                        "id" : "5fb09b5f594f0000350074da"
                },
                "5" : {
                        "id" : "5fb09b5f594f0000350074db"
                },
                "6" : {
                        "id" : "5fb09b5f594f0000350074dc"
                },
                "7" : {
                        "id" : "5fb09b5f594f0000350074dd"
                },
                "8" : {
                        "id" : "5fb09b5f594f0000350074de"
                },
                "9" : {
                        "id" : "5fb09b5f594f0000350074df"
                }
        },

what is going wrong?

Thank you