Hi Thomas,
Sure, what you then would do is to move the "limit" back to the limit clause
Match (:Node {id:"unique-string"})-[:NEXT*1..]->(m)
WHERE m.prop = "value"
Return m
limit 20
We'll add using indexes for ordering at some point but I'm not sure when
and how.
Michael
On Sat, Sep 13, 2014 at 2:53 AM, <[email protected]> wrote:
> Thanks Michael for your answer.
>
> If I understand correctly, your method would require to manually maintain
> a chain of relationships between my nodes, in the order of the field I want
> the results to be ordered by, right?
> Which means, if I want my paginated results to be ordered by "name", I
> need to manually chain:
> (n1 {name:"a"})-[:NEXT]->(n2 {name:"aa"})-[:NEXT]->(n3 {name:"b"})-...
>
> There are some examples in the graph-databases book (free pdf on
graphdatabases.com) on how to maintain such an list automatically on insert
of new data.
Michael
> Would that work if I also wanted to filter the results with a WHERE clause
> on some other field of my nodes? I guess it would somehow break the chain...
>
> Cheers
> Thomas
>
> On Saturday, September 13, 2014 3:20:48 PM UTC+8, Michael Hunger wrote:
>>
>>
>>
>> Sent from mobile device
>>
>> Am 13.09.2014 um 05:31 schrieb [email protected]:
>>
>> Hi everyone,
>>
>> (sorry for the long post to follow!)
>>
>>
>> No worries
>>
>>
>> We have an existing platform relying on CouchDB (Cloudant, actually) and
>> I'm evaluating a potential migration to Neo4j. The good thing with having
>> an existing version is that I've already been through many pitfalls, so now
>> I can consider them with Neo4j. One of them is *pagination*.
>>
>> CouchDB has a 'skip' feature that is similar to Neo4j. The doc clearly
>> states that it should not be used for pagination, because it incurs
>> potential performance issues when skipping lots of large pages (if you take
>> 10 items by skipping 10, the DB will still fetch 20 and return the last 10).
>>
>> *So first question*: is it the same with Neo4j?
>>
>>
>> Yes. In embedded mode you can keep the result open though as well as on
>> the remote endpoint where you can within a tx can continue to read
>>
>>
>> In case it is (and I believe it is!), I would like to see whether
>> CouchDB's approach to pagination would be applicable. The strategy here is
>> to fetch n+1 items, and pass the last one as a cursor/bookmark than will be
>> used as a starting point for the next query. This sounds easy, but gets
>> tricky if you order by a field that is not unique. Let me take an example.
>>
>> Say I have this kind of node:
>> (:Node {id:"unique-string", name:"not-unique-string"})
>>
>> *My second question is*: if I want to query these nodes, ordered by
>> name, is there a way to implement the cursor technique I mentioned before?
>>
>>
>> In a graph you can link these nodes in an ordered list by name and then
>> follow the link
>>
>> For the next page your starting node would be the last node of the
>> previous result
>>
>> Match (:Node {id:"unique-string"})-[:NEXT*1..20]->(m)
>> Return m
>>
>> For the next page you pass in the last id
>>
>>
>> Also, *subsidiary question*: I've read that 'order by' incurs a full
>> scan, but is it also the case if I index the targeted field?
>>
>>
>> Yep, right now it is for the normal order by clause
>>
>>
>> Thanks all for helping me get familiar with that exciting platform!
>> Thomas
>>
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