How can I rename a field nested in a list of objects stored in a list?

[Paul_Mallon]

Hi there,
This is my first post here, I’m fairly new to mongoDB.
I have the following structure in a collection called agreements:
basicData.owners.relatedJson.basicData.devices.equipmentID

Where owners and devices are lists of objects.
This structure is quite complex, and it’s worth noting that there is no guarantee the relatedJson object or the devices list exist.
I would like to rename the field eqiupmentID to equipmentId.

I have tried modifying a similar query that renames a field in a nested object in a nested list to suit this purpose, so far I’ve got the following:

db.serviceAgreement.updateMany({"basicData.serviceRecipients.relatedJson.basicData.devices.equipmentID": {$exists: true}},
    [
        {
            $set: {
                "basicData.serviceRecipients": {
                    $map: {
                        input: "$basicData.serviceRecipients",
                        in: {
                            $mergeObjects: [
                                "$$this",
                                {
                                    $cond: [
                                        {
                                            $ne: [
                                                "$$this.relatedJson",
                                                undefined
                                            ]
                                        },
                                        {
                                            relatedJson : {

                                                $mergeObjects: [
                                                    "$$this.relatedJson.basicData",
                                                    {
                                                        $cond: [
                                                            {
                                                                $ne: [
                                                                    "$$this.relatedJson.basicData",
                                                                    undefined
                                                                ]
                                                            },
                                                            {
                                                                basicData : {

                                                                    $mergeObjects: [
                                                                        "$$this.relatedJson.basicData",
                                                                        {
                                                                            $cond: [
                                                                                {
                                                                                    $ne: [
                                                                                        "$$this.relatedJson.basicData.devices,
                                                                                        undefined
                                                                                    ]
                                                                                },
                                                                                {
                                                                                    "$$this.devices": {
                                                                                        $map: {
                                                                                        
                                                                                        }
                                                                                    }   
                                                                                },
                                                                                {}
                                                                            ]
                                                                        }
                                                                    ]
                                                                }
                                                            },
                                                            {}
                                                        ],
                                                    }
                                                ]
                                            }
                                        },
                                        {}
                                    ]
                                }
                            ]
                        }
                    }
                }
            }
        },
        {
            $unset: "basicData.serviceRecipients.relatedJson.basicData.devices.equipmentID"
        }
    ])

I’m now looking at "$$this.devices": and calling $map in there, and mapping each device with the new name. Is this the correct approach? will this work?
My original plan was to add the new field equipmentId and remove the old one (see the $unset call at the end) but I cannot get that to work when working with lists of lists.
Any advice either way would be greatly appreciated.
I would prefer to add the new field the remove the old one WITHOUT having to specify every other field in each device object as some of those may contain more nested objects.

[Paul_Mallon]

I managed to figure it out! The code below does exactly what I’m looking for.
I’d be curious to know if there’s a more efficient way to do this :slightly_smiling_face :

db.collection.updateMany({
 "basicData.owners.relatedJson.basicData.devices.equipmentID": {
            $exists: true
        }
    },
    [
        {
            $set: {
                "basicData.owners": {

                    $map: {
                        input: "$basicData.owners",
                        in: {

                            $mergeObjects: [
                                "$$this",
                                {
                                    $cond: [
                                        {
                                            $ne: [
                                                "$$this.relatedJson",
                                                undefined
                                            ]
                                        },
                                        {
                                            "relatedJson": {
                                                $mergeObjects: [
                                                    "$$this.relatedJson",
                                                    {
                                                        $cond: [
                                                            {
                                                                $ne: [
                                                                    "$$this.relatedJson.basicData",
                                                                    undefined
                                                                ]
                                                            },
                                                            {
                                                                "basicData": {
                                                                    $mergeObjects: [
                                                                        "$$this.relatedJson.basicData",
                                                                        {
                                                                            $cond: [
                                                                                {
                                                                                    $ne: [
                                                                                        "$$this.relatedJson.basicData.devices",
                                                                                        undefined
                                                                                    ]
                                                                                },
                                                                                {
                                                                                    "devices": {
                                                                                        $map: {
                                                                                            input: "$$this.relatedJson.basicData.devices",
                                                                                            in: {
                                                                                                $mergeObjects: [
                                                                                                    "$$this",
                                                                                                    {
                                                                                                        equipmentId: "$$this.equipmentID",

                                                                                                    }
                                                                                                ]
                                                                                            }
                                                                                        }
                                                                                    }
                                                                                },
                                                                                {},
                                                                            ]
                                                                        }
                                                                    ]
                                                                }
                                                            },
                                                            {},
                                                        ]
                                                    }
                                                ]
                                            }
                                        },
                                        {},
                                    ]
                                }
                            ]
                        }
                    }
                }
            }
        },
        {
            $unset: "basicData.owners.relatedJson.basicData.devices.equipmentID"
        }
    ])