DBRefs support? about mongo-rust-driver HOT 2 CLOSED

Hi @nasa8x, thanks for reaching out!

The Rust driver does not provide a DBRef type, however a DBRef is really just a MongoDB document with keys named $ref, $id, and optionally $db so if needed you can work with existing data containing DBRefs just by using the Document type.

Assuming that the two collections you need to join data from are in the same database, the best way to accomplish something similar to Mongoose's populate functionality in the Rust driver with a single query to get all of the data would be using aggregate with $lookup.

For example if you have both a books and and an authors collection:

let id = ObjectId::new();
db.collection("authors").insert_one(doc! { "name": "Albert Camus", "_id": id }, None).await?;
db.collection("books").insert_one(doc! { "name": "The Stranger", "author_id": id }, None).await?;
let pipeline = vec![doc! {
    "$lookup": {
        "from": "authors",
        "localField": "author_id",
        "foreignField": "_id",
        "as": "authorInfo",
    }
}];
let result = db.collection::<Document>("books").aggregate(pipeline, None).await?;

The resulting documents in the cursor (as printed in the MongoDB shell) would be:

[
  {
    _id: ObjectId("6189a602f456a0693242b073"),
    name: 'The Stranger',
    author_id: ObjectId("6189a5b0f456a0693242b072"),
    authorInfo: [
      {
        _id: ObjectId("6189a5b0f456a0693242b072"),
        name: 'Albert Camus'
      }
    ]
  }
]

Note that in the above case a manual reference to the _id for the author document is used rather than a DBRef, since only the _id was needed for my query. However, if the data for the author was stored as a DBRef (in the same database) the same approach would work, you could just reference the $id key from the DBRef instead.

If the collections are in separate databases, unfortunately at this point in time $lookup would not be an option, and you would need to do two separate queries with e.g. find to separately retrieve the documents.

You can see some documentation on the $lookup stage here.

Let me know if that makes sense or if you have further questions!

from mongo-rust-driver.

@kmahar Very clear, thank you very much.

from mongo-rust-driver.