CODEWITHSUNDEEP
couchdb
Akif Hadziabdic
Akif Hadziabdic

Reputation: 2890

CouchDB query for more dynamic values

I have more "Location documents" in my couchdb with longitude and latitude fields. How to find all location documents in database which distance to provided latitude and longitude is less than provided distance.

Upvotes: 1

Views: 797

Answers (3)

Nuno Cruces
Nuno Cruces

Reputation: 1743

Vanilla CouchDB isn't really built for geospacial queries.

Your best bet is to either use GeoCouch, CouchDB-Lucene or something similar.

Failing that, you could emit a Geohash from your map function, and do range queries over those.

Caveats apply. Queries around Geohash "fault lines" (equator, poles, longitude 180, etc) can give too many or too little results.

There are multiple JavaScript libraries that can help convert to/from Geohash, as well as help with some of those caveats.

Upvotes: 1

Petter
Petter

Reputation: 1337

CouchDB is not built for dynamic queries, so there is no good/fast way of implementing it in vanilla couchDB. If you know beforehand which locations you want to calculate the distance from you could create a view for each location and call it with parameters ?startkey=0&endkey=max_distance

function(doc) {
  function distance(...){ /* your function for calculating distance */ }
  var NY = {lat:40,lon:73}
  emit( distance(NY,doc), doc._id);
}

If you do not know the locations beforehand you could solve it by using a temporary view, but I would strongly advise against it since it's slow and should only be used for testing.

Upvotes: 0

ermouth
ermouth

Reputation: 844

There is a way how to achieve it using vanilla CouchDB, but it‘s bit tricky.

You can use the fact you can apply two map functions during one request. Second map function can be created using list mechanics.

Lists are not very efficient from computational side, they can‘t cache results as views. But they have one unique feature – you can pass several arguments into list. Moreover, one of your arguments can be, for example, JS code, that is eval-ed inside list function (risky!).

So entire scheme looks like this:

  • Make view, that performs coarse search
  • Make list, that receives custom params and refines data set
  • Make client-side API to ease up querying this chain.

Can‘t provide exact code for your particular case, many details are not clear, but it seems that coarse search must group results to somehow linearly enumerated squares, and list perform more precise calculations.

Please note, that scheme might be inefficient for large datasets since it‘s computationally hungry.

Upvotes: 1

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