I am trying to optimise the following scans
into a single scan
(or query
). The only way I see is to use to use a OR
comparator using DynamoDB . I am using dynogels
(fork of vogels
) in my application but sadly I am not aware of any OR
query functionality in there.
let arrivals = yield Reservation.scan() .where('room').equals(room) .where('arrival').between(from, to) .execAsync().then((reply) => reply.Items.map((item) => item.get())); let departures = yield Reservation.scan() .where('room').equals(room) .where('departure').between(from, to) .execAsync().then((reply) => reply.Items.map((item) => item.get())); let combined = arrivals.concat(departures); return Promise.resolve(combined);
Proposed optimisation:
return Reservation.scan() .where('room').equals(room) .where('arrival').between(from, to) .or.where('departure').between(from, to) .execAsync().then((reply) => reply.Items.map((item) => item.get()));
The scans get me the reservations that end ( departure
) or start ( arrival
) (or both) in a specified date range ( from
, to
).
I think this can be achieved using filterexpression
.
Sample code using filterexpression:-
const scanItem = Reservation.scan().filterExpression('room = :idVal AND ((arrival BETWEEN :arrDateVal1 AND :arrDateVal2) OR (departure BETWEEN :depDateVal1 AND :depDateVal2)) ')
.expressionAttributeValues({ ':idVal' : '2', ':arrDateVal1' : '21-APR-2017', ':arrDateVal2' : '23-APR-2017'
,':depDateVal1' : '21-APR-2017', ':depDateVal2' : '23-APR-2017'});
scanItem.exec((err, result) => {if(!err) {console.log(JSON.stringify(result,undefined, 2))}});
Note:-
Not sure whether you wanted to specifically use where
rather than filterexpression
(or) just wanted to achieve the result regardless of where
or filterexpression
.
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