Hi Mike,
so your data might look like
{ "name": "John", "age": 35 }
{ "name": "Lisa", "age": 8 }
{ "name": "Tim", "age": 17 }
{ "name": "Marry", "age": 84 }
and you want to set { "selected": true } on them until the sum of ages
reaches Z, let's say 50.
John would be selected (sum = 35), Lisa as well (sum = 35 + 8 = 43), but
not Tim (sum = 35 + 8 + 17 = 60) and thus also not Marry.
LIMIT can not be a runtime-evaluated expression, and a summation with
COLLECT AGGREGATE can not be stopped with a FILTER (will only post-filter
result).
Thus, the only way to implement this in vanilla AQL that I found is to sum
up increasing slices of the data (John, John+Lisa, John+Lisa+Tim,
John+Lisa+Tim+Marry), FILTER out all which which exceed Z and return the
last "good" slice:
LET data = [
{ "name": "John", "age": 35 },
{ "name": "Lisa", "age": 8 },
{ "name": "Tim", "age": 17 },
{ "name": "Marry", "age": 84 }
]
FOR i IN 1..LENGTH(data)
FILTER SUM(SLICE(data, 0, i)[*].age) <= 50
RETURN data[i-1]
This is not particularly efficient, but should work for tiny datasets. If
you want to do this on larger datasets, I would recommend to write a
JavaScript transaction that requests all documents, but only processes the
first n (until the age sum reaches Z), then update those documents. If you
know that the maximum number of documents will never be above e.g. 100,
then you can apply a limit in the initial query to improve server
performance.
Two things that crossed my mind:
- You don't have a SORT statement in your query, which means the order in
which documents are returned and selected may change between any two
queries. Doesn't it matter for your use case which documents get selected?
- You want to UPDATE certain documents with a "selected" attribute. What do
you want to use this for though? Would it be possible run a single query
server-side, and select and process the rest on the client-side maybe?
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