Filter arrays in mongodb - mongodb

Question

I have a collection where each document contains 2 arrays of documents as below.
{
all_users:[
{
id:1,
name:"A"
},
{
id:2,
name:"B"
},
{
id:3,
name:"C"
}
]
selected_users:[
{
id:1,
name:"A"
},
{
id:2,
name:"B"
}
]
}
Is it possible to merge the 2 arrays by adding a field selected and assigning a value to it based on whether the name of the user is present in a document in the selected_users array as follows.
{
all_users:[
{
id:1,
name:"A",
selected:"yes"
},
{
id:2,
name:"B",
selected:"yes"
},
{
id:3,
name:"C",
selected:"no"
}
]
}
I want to check by id or name since the documents may contain additional fields. I can't figure out how to achieve this.

Answer 1

$map to iterate loop of all_users array
$cond check condition if id is in selected users id then return "yes" otherwise "no" in selected field
$mergeObject to merge current user object with above selected field
db.collection.aggregate([
{
$project: {
all_users: {
$map: {
input: "$all_users",
in: {
$mergeObjects: [
"$$this",
{
selected: {
$cond: [
{ $in: ["$$this.id", "$selected_users.id"] },
"yes",
"no"
]
}
}
]
}
}
}
}
}
])
Playground

Answer 2

If you are using the Robo Mongo 3T, you can use JavaScript, so you can do something like that:
db.collection.find({}).forEach(doc => {
doc.all_users.map(au => {
const su = doc.selected_users.find(su => su.id === au.id);
au.selected = su === undefined;
});
delete doc.selected_users;
db.collection.save(doc);
})
I would advise you to create a Backup of the collection beforehand. :)