RethinkDB: how to append to an array in a nested structure - rethinkdb

Question

I am trying to append to an array in a nested field, which I have to find based on runtime information.
Here's an example:
r.db("test")
.table("test")
.insert({ "stock": [{ "bin":"abc", "entries":[{ "state":1 }] }] })
The idea is that the document contains a "stock" key, which is an array of multiple "storage bins". Each bin has a name and a number of entries. I need to be able to append to entries in one of the bins, atomically, without affecting other bins.
I tried this approach:
r.db("test")
.table("test")
.update(function(item) {
return {"stock": item("stock")
.filter({ "bin": "abc" })
.append({ "state":42 })
}
})
…but that does not append at the right level, and I am not certain if it will preserve existing bins with names other than "abc".

Answer 1

When updating an element of an array, you should use changeAt with an index, or map over the array instead of using filter.
Here is what that query might look like:
r.table("test")
.update(function(item){
return {"stock": item("stock").map(function(stock){
r.branch(stock.hasFields({"bin": "abc"})
stock.merge({"entries": stock("entries").append({"state": 42})}),
stock)})}})
Alternatively, if you stored your entries in an object instead of an array, like this:
{ "stock": {"abc": {"entries":[{ "state":1 }] }} }
The update query might look like this:
r.table("test")
.filter(r.row.hasFields({"stock": {"abc": true}}))
.update({"stock": {"abc": r.row("stock")("abc").append({"state": 42})}})