If I use Mongoose to run a query on a schema that has a reference to another model (in this case, a BlogPost model with a property author which references another Author model).
let posts = await BlogPost.find({}, "title author").populate("author","name bio").lean()
By passing lean() I am supposed to get a POJO back like this:
[{
"_id": "602828eaff09bca9c3af2dbb",
"author": {
"_id": "602433bd98d380443ef9aeb7",
"name": "Matt",
"bio": "matt is cool"
},
"title": "Hello World",
"__v": 0
}, {
"_id": "6048b8cb0200e51b4f2486c8",
"author": {
"_id": "602433bd98d380443ef9aeb7",
"name": "Matt",
"bio": "matt is cool"
},
"title": "Another Blog post",
"__v": 0
}]
However if I modify for example
posts[0].author.name = "Test"
then ALL the posts with this author in the array are modified:
[{
"_id": "602828eaff09bca9c3af2dbb",
"author": {
"_id": "602433bd98d380443ef9aeb7",
"name": "Test",
"bio": "matt is cool"
},
"title": "Hello World",
"__v": 0
}, {
"_id": "6048b8cb0200e51b4f2486c8",
"author": {
"_id": "602433bd98d380443ef9aeb7",
"name": "Test",
"bio": "matt is cool"
},
"title": "Another Blog post",
"__v": 0
}]
If instead I only wanted to affect the first object in the array, what should I do?
The populate function in Mongoose https://mongoosejs.com/docs/api/query.html#query_Query-populate has an option clone:true
[options.clone=false] «boolean» When you do BlogPost.find().populate('author'), blog posts with the same author will share 1 copy of an author doc. Enable this option to make Mongoose clone populated docs before assigning them.
So the correct code would be something like
let posts = await BlogPost.find({}, "title author").populate({path:"author", fields:"name bio", clone:true}).lean()
Thanks to @buithienquyet in the comments for the pointers