Wow, nice, first there is no sort, since it does not matter which ones are selected, any previously unselected document can be chosen. Im using this in an AQL TRANSACTION, where i pick a set of documents whose sum of age does not exceed some value, and mutate them atomically and return them to the client (its important that they are acted on atomically).
Mike On Mon, Jan 15, 2018 at 12:39 PM Simran Brucherseifer <[email protected]> wrote: > 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? > > -- > You received this message because you are subscribed to a topic in the > Google Groups "ArangoDB" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/arangodb/BWTNkZ9e9W4/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > [email protected]. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "ArangoDB" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
