I am trying to do manual pagination using cassandra-driver npm module by storing pageState in session but it throws error TypeError has no copy method.

[Ravikant Sinha]

Hi,

I am trying to do manual pagination using cassandra-driver npm module. Pagination works fine when I am storing pagestate in global variable  but when I store pagestate in session (using node.js express project), it throws error TypeError has no copy method.

Following is the snippet used in one of the routes in the express:

var options={pageState:req.session.pageStateMeta,prepare :  1 , fetchSize :  50};

var data=[];

var responseObj=DMUtil.Response();

cassandraClient.eachRow(query,[],options,function (n, row) {

          

            data.push(row);

        }, function (err, result) {

            // End callback.

            // Store the paging state.

          

            if(!err && result){

               

                req.session.pageStateMeta = result.meta.pageState;

              

            }

            responseObj.responseData=data;

            res.send(responseObj);

        });

In first call to this route  its getting data but in next call, its not able to use req.session.pageStateMeta  and throws following error

 [TypeError: Object 0,0,0,61,0,8,0,0,1,74,75,62,148,0,0,0,2,117,115,0,0,4,0,0,0,7,0,0,19,68,73,83,80,76,65,89,95,65,68,86,69,82,84,73,83,73,78,71,0,0,3,65,76,76,0,0,4,7,173,159,179,0,0,0,0,127,255,255,205 has no method 'copy']

Has anyone of you faced this issue.

[Krassimir Fotev]

We've exposed a nextPage method in the manual-paging cassandra-driver branch.

You call res.nextPage() to advance to the next chunk. It is far easier than storing and reusing state.

I still owe Jorge support for stream throttling. Will do as soon things on Peerbelt's side calm a bit (funding, team, clients).

Cheers, 

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Krassimir Fotev

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kfo...@peerbelt.com

973 412 8273

[Ravikant]

Thanks Krassimir for prompt reply.Could you please give small code snippet for the same ?. Basically its web app in express. So, things should work for concurrent user, that's here session is needed. It would be great, If you could suggest something better.

Thanks & Regards
Ravikant

[Jorge Bay Gondra]

Hi Ravikant,

In your case, you will need the actual pageState, so you are using it correctly except from one detail.

The pageState in the clientOptions is a Buffer and it looks like you are not providing one.

The easiest solution would be to store the pageState in an hex string and then reuse it.

Storing it in the session:

req.session.pageStateMeta = result.meta.pageState.toString('hex');

Use it:

var options={pageState: new Buffer(req.session.pageStateMeta, 'hex')};

Hope it helps,

Jorge

[Ravikant]

Thanks a lot Jorge. You made my  day.

[Richard Armstrong]

Hi Jorge,

On this same topic, when doing manual paging is there any way the client will let you know when you've reached the last page? 

I've found that when I using the pageState it will automatically loop back to the first page unless I manually write a break (i.e. if(firstId == currentId) then exit) 

Thanks

Richard

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Krassimir Fotev

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http://www.peerbelt.com

kfo...@peerbelt.com

973 412 8273

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Thanks & Regards
Ravikant

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[Jorge Bay Gondra]

Hi Richard,

Yes, when the pageState is null, there are no more pages. Having a not null pageState means that there are further result pages.

BTW: I will add it to the paging documentation, as it is not noted there.

Thanks,

Jorge

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[Richard Armstrong]

Thanks Jorge, that makes life a lot easier!

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[Jorge Bay Gondra]

Added to the docs: A non-null pageState value means that there are additional result pages by @DataStaxDocs team

[Richard Armstrong]

Great thanks -  I realise the intention of this is for paging but it also is a great feature for batching - as a suggestion this is the api I ended up creating (hiding the internals of the pageState)

e.g. client.eachRow(query, [], { prepare :  1 , fetchSize :  1000 },  function (n, row) {

}, function(err, result, next){

next()

})

Am sure you have loads of other features to implement, but just thought which others might find useful.