Nested Upserts

[RoboZoom]

Hi,

I wrote a utility for upserts of objects in nested arrays. Is this something you'd be interested in incorporating into the library? If so, I'd be happy to contribute it!

[zookzook]

I think this is a topic for the Repo module? Could you provide an example?

[RoboZoom]

If you have a data structure in a collection "foos" like:

{
    "foo": {
        "id": "1a",
        "bar": {
            "baz": [
                {
                    "id": "1",
                    "name": "First",
                    "description": "Some information"
                },
                {
                    "id": "2",
                    "name": "Second",
                    "description": "Some Additional Information"
                },
                {
                    "id": "3",
                    "name": "Third",
                    "description": "This is the third item"
                }
            ]
        }
    }
}

If you want to upsert into the baz array, there's no terse way of doing this with Mongo. You either need to make it into a multiple operation type transaction (check of the new value is in the array - if so, edit the array... if not, push it to the array), or you can build an aggregation pipeline .

I've implemented a general form of the aggregation pipeline which takes a key-path to the array, a key to match identity amongst the array items, and it executes a partial update against an element that already exists or pushes it into the array.

For example

upsert_nested("foos", "1a", "foo.bar.baz", "id", "%{id: "3", name: "Third +")

Would change the last element to:

{
                    "id": "3",
                    "name": "Third +",
                    "description": "This is the third item"
                }

I think it would need to be a little bit more general than it currently is (and I may need your help to best do that) but it's an 80% solution right now.

[zookzook]

It could be a nice extension, but it uses some kind of id which depends on the use case:

upsert_nested("foos", "1a", "foo.bar.baz", "id", "%{id: "3", name: "Third +")

This approach assumes that the data structure has a concept of id. But it is not clear, that the second parameter is the value of an attribute named id.

I think the example is not correct: instead of

{
    "foo": {
        "id": "1a",
        "bar": {

the document should look like:

{
    "id": "1a",
    "foo": {
        "bar": {

?

Someone would use "_id" or "uuid" as the identifier. Maybe the API can look like this:

upsert_one_nested(collection, query, path, subquery, doc)

The function will use the query to find the document in the collection, the path points to the nested documents. The subquery is used to find the nested document, which is updated to doc or when missing, it is inserted under the path.

upsert_one_nested("foos", %{id: "1a"}, "foo.bar.baz", %{id: "3"}, %{name: "Third +"})