[MongoDB]: Changing the type of values in all array fields - mongodb

Question

I have the authors and books test collections which have a many-to-many relationship between them.
> db.books.find()
[
{
_id: ObjectId("60a676f24312c6d8ea7bd6ec"),
title: '300 years of peanut juggling: A longitudinal analysis.',
inPrint: true,
authors: [ '60a673c44312c6d8ea7bd6e9', '60a673c44312c6d8ea7bd6ea' ]
},
{
_id: ObjectId("60a676f24312c6d8ea7bd6ed"),
title: "Mystery Overflow: murder and chaos on the Web's biggest developer Q & A platform.",
inPrint: true,
authors: [ '60a673c44312c6d8ea7bd6eb' ],
edition: 2
}
]
> db.authors.find()
[
{
_id: ObjectId("60a673c44312c6d8ea7bd6e9"),
name: 'Jason Filippou',
age: 33,
nationalities: [ 'GRC, CND' ],
books: [ '60a676f24312c6d8ea7bd6ec' ]
},
{
_id: ObjectId("60a673c44312c6d8ea7bd6ea"),
name: 'Mary Chou',
age: 39,
nationalities: [ 'USA' ],
books: [ '60a676f24312c6d8ea7bd6ec' ]
},
{
_id: ObjectId("60a673c44312c6d8ea7bd6eb"),
name: 'Max Schwarz',
age: 42,
job: 'pilot',
books: [ '60a676f24312c6d8ea7bd6ed' ]
}
]
I implement the relationship externally, as can be seen by the authors and books fields. However, I have made the mistake of having the arrays of references be raw strings, instead of ObjectId types. This means that my joins as required by, e.g, $lookup()) fail.
I tried to mass update all the strings to make them ObjectIds using the command:
db.books.find({}).forEach(book => book.authors.forEach(id => ObjectId(id)))
While the command worked, the original data did not change:
> db.books.find({}).forEach(book => book.authors.forEach(id => ObjectId(id)))
> db.books.find()
[
{
_id: ObjectId("60a676f24312c6d8ea7bd6ec"),
title: '300 years of peanut juggling: A longitudinal analysis.',
inPrint: true,
authors: [ '60a673c44312c6d8ea7bd6e9', '60a673c44312c6d8ea7bd6ea' ]
},
{
_id: ObjectId("60a676f24312c6d8ea7bd6ed"),
title: "Mystery Overflow: murder and chaos on the Web's biggest developer Q & A platform.",
inPrint: true,
authors: [ '60a673c44312c6d8ea7bd6eb' ],
edition: 2
}
]
> db.authors.find()
[
{
_id: ObjectId("60a673c44312c6d8ea7bd6e9"),
name: 'Jason Filippou',
age: 33,
nationalities: [ 'GRC, CND' ],
books: [ '60a676f24312c6d8ea7bd6ec' ]
},
{
_id: ObjectId("60a673c44312c6d8ea7bd6ea"),
name: 'Mary Chou',
age: 39,
nationalities: [ 'USA' ],
books: [ '60a676f24312c6d8ea7bd6ec' ]
},
{
_id: ObjectId("60a673c44312c6d8ea7bd6eb"),
name: 'Max Schwarz',
age: 42,
job: 'pilot',
books: [ '60a676f24312c6d8ea7bd6ed' ]
}
]
What is my mistake here?

Answer 1

If you decide to update all books string to ObjectId, u can use update-documents-with-aggregation-pipeline
db.authors.updateMany({},[
{
"$addFields": {
"books": {
"$map": {
"input": "$books",
"in": {
"$toObjectId": "$$this"
}
}
}
}
}
])