Overwrite value and create key while update query in mongodb - mongodb

Question

I have a mongodb collection that looks like this:
{
"_id" : ObjectId("60471bd482c0da3c0e70d26f"),
"owner" : "John",
"propAvailable" : {
"val1" : true
}
},
{
"_id" : ObjectId("60471bd482c0da3c0e76523f"),
"owner" : "Matt",
"propAvailable" : {
"val1" : {
"val2" : true
}
}
I need to run an update query on this collection that will update the value of the 'propAvailable' key such that
db.collection('props').update({'owner' : 'John'} , {$set : {'propAvailable.val1.val2' : true}});
This query works if the document already looks like the second one but gives the error:
Cannot create field 'val2' in element {'val1': true} if the document format is the first one. Is there a way to write this query so that it overwrites the boolean 'true' and replaces it with the object {'val2' : true}

Answer 1

You can use:
db.collection.update({
"owner": "John"
},
{
$set: {
"propAvailable.val1": {
val2: true
}
}
})
To create val2: true inside propAvailable.val1 and replace its current content.
As you can see working on the playground

Answer 2

If you're using Mongo version 4.2+ you can use pipelined updates to achieve this, like so:
db.collection.updateMany({
owner: "John"
},
[
{
$set: {
"propAvailable.val1": {
$mergeObjects: [
{
$cond: [
{
$eq: [
"object",
{
$type: "$propAvailable.val1"
}
]
},
"$propAvailable.val1",
{}
]
},
{
val2: true
}
]
}
}
},
])
Mongo Playground
For older mongo versions this is impossible to do in 1 query if objects potentially have additional fields under val1 you want to preserve. You will have to either read and update, or execute two different updates for each case.