Dynogels：使用OR比较查询

Question

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 ).

Answer 1

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 .