Class: Sunspot::DSL::RestrictionWithNear

Inherits:
Restriction show all
Defined in:
sunspot/lib/sunspot/dsl/restriction_with_near.rb

Instance Method Summary (collapse)

Constructor Details

- (RestrictionWithNear) initialize(field, scope, query, negated)

A new instance of RestrictionWithNear 



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# File 'sunspot/lib/sunspot/dsl/restriction_with_near.rb', line 4

def initialize(field, scope, query, negated)
  super(field, scope, negated)
  @query = query
end

Instance Method Details

- (Object) near(lat, lng, options = {})

Perform a Geohash-based location restriction for the given `location` field. Though this uses the same API as other attribute-field restrictions, there are several differences between this and other scoping methods:

  • It can only be called from the top-level query; it cannot be nested in a `dynamic`, `any_of`, or `all_of` block. This is because geohash queries are not sent to Solr as filter queries like other scopes, but rather are part of the fulltext query sent to Solr.

  • Because it is included with the fulltext query (if any), location restrictions can be given boost. By default, an “exact” (maximum-precision) match will give the result a boost of 1.0; each lower level of precision gives a boost of 1/2 the next highest precision. See below for options to modify this behavior.

What is a Geohash?

Geohash is a clever algorithm that creates a decodable digest of a geographical point. It does this by dividing the globe into quadrants, encoding the quadrant in which the point sits in the hash, dividing the quadrant into smaller quadrants, and repeating an arbitrary number of times (the “precision”). Because of the way Geohash are built, the shared Geohash prefix length of two locations will usually increase as the distance between the points decreases. Put another way, the geohashes of two nearby points will usually have a longer shared prefix than two points which are distant from one another.

Read more about Geohashes on Wikipedia or play around with generating your own at geohash.org.

In Sunspot, GeoHashes can have a precision between 3 and 12; this is the number of characters in the hash. The precisions have the following maximum bounding box sizes, in miles:

3
389.07812
4
97.26953
5
24.31738
6
6.07935
7
1.51984
8
0.37996
9
0.09499
10
0.02375
11
0.00594
12
0.00148

Score, boost, and sorting with location search

The concept of relevance scoring is a familiar one from fulltext search; Solr (or Lucene, actually) gives each result document a score based on how relevant the document’s text is to the search phrase. Sunspot’s location search also uses scoring to determine geographical relevance; using boosts, longer prefix matches (which are, in general, geographically closer to the search origin) are assigned higher relevance. This means that the results of a pure location search are roughly in order of geographical distance, as long as no other sort is specified explicitly.

This geographical relevance plays on the same field as fulltext scoring; if you use both fulltext and geographical components in a single search, both types of relevance will be taken into account when scoring the matches. Thus, a very close fulltext match that’s further away from the geographical origin will be scored similarly to a less precise fulltext match that is very close to the geographical origin. That’s likely to be consistent with the way most users would expect a fulltext geographical search to work.

Options

:precision
The minimum precision at which locations should match. See the table of precisions and bounding-box sizes above; the proximity value will ensure that all matching documents share a bounding box of the corresponding maximum size with your origin point. The default value is 7, meaning all results will share a bounding box with edges of about one and a half miles with the origin.
:boost
The boost to apply to maximum-precision matches. Default is 1.0. You can use this option to adjust the weight given to geographic proximity versus fulltext matching, if you are doing both in a search.
:precision_factor
This option determines how much boost is applied to matches at lower precisions. The default value, 16.0, means that a match at precision N is 1/16 as relevant as a match at precision N+1 (this is consistent with the fact that each precision’s bounding box is about sixteen times the size of the next highest precision.)

Example

  Sunspot.search(Post) do
    fulltext('pizza')
    with(:location).near(-40.0, -70.0, :boost => 2, :precision => 6)
  end


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# File 'sunspot/lib/sunspot/dsl/restriction_with_near.rb', line 116

def near(lat, lng, options = {})
  @query.fulltext.add_location(@field, lat, lng, options)
end