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Full Text Search

Couchbase Server Full Text Search (FTS) enables you to create, manage, and query full text indexes on JSON documents stored in a Couchbase bucket. You should use search instead of query when your application requires natural language processing when searching.

Couchbase FTS is similar in purpose to other search software such as ElasticSearch or Solr. Couchbase FTS is not intended as a replacement for third party search software if search is at the core of your application. It is a simple and lightweight way to add search to your Couchbase data without deploying additional software and servers. If you have many queries which look like SELECT ... field1 LIKE %pattern% OR field2 LIKE %pattern, then full-text search may be right for you.

Our first search query will be done against the travel-sample bucket (install it, if you haven’t done so already).

  1. Go to the Couchbase Web Console (for example, http://localhost:8091) and log in with your administrative username and password.

  2. Select Indexes  Full Text (at the top bars).

  3. In the dropdown menu on the top left (-- choose full text index or alias --) select travel-search.

  4. In the input box (on the right), type cheese and click Search.

You will see a list of document IDs that contain the given search term. You can click on any document ID to see the full document. You can also click on Advanced to see the raw query as it is sent over the REST API. If you click on the command-line curl example checkbox, you can simply copy/paste the output to your terminal and execute the search again.

Here’s a similar version of the search done using curl on the command line:

curl -XPOST -H "Content-Type: application/json" \
    http://localhost:8094/api/index/travel-search/query \
    -d '{"query":{"query":"cheese"}, "size": 1}' | json_pp

(Note that json_pp is just a JSON formatter. You can omit the pipe if you do not have it installed).

   "hits" : [
         "index" : "travel-search_2c8e9e3d5a3638a8_b7ff6b68",
         "score" : 1.20476244729454,
         "locations" : {
            "name" : {
               "cheese" : [
                     "end" : 12,
                     "array_positions" : null,
                     "start" : 6,
                     "pos" : 2
         "id" : "landmark_27808"

(Most of the output has been redacted)

The same query using the Python SDK:

from couchbase.bucket import Bucket
import couchbase.fulltext as FT

cb = Bucket()
results = cb.search('travel-search', FT.StringQuery('cheese'), limit=5)
for hit in results:
    print('Found in document ID={}. Score={}'.format(hit['id'], hit['score']))
Found in document ID=landmark_27808. Score=1.20476244729
Found in document ID=landmark_8689. Score=0.961675281363
Found in document ID=landmark_1154. Score=0.883110932061
Found in document ID=landmark_1163. Score=0.846040674514
Found in document ID=landmark_15133. Score=0.81847489864

The result contains one or more hits, where each hit contains information about the location of the match within a document. This includes the relevance score as well as the location where the match was found.

Making Your Bucket Searchable

In order to execute a search query you must first define a search index. You can define a search index by using the Couchbase Web Console.

  1. Go to the Couchbase Web Console (for example, http://localhost:8091) and log in with your administrative username and password.

  2. Select Indexes  Full Text  New Full Text Index

  3. Type the desired name of the search index in the Index Name field.

  4. Select the bucket you would like to associate the search with in the Bucket field

The default settings are sufficient for most cases. You can edit the index later, specifying how certain fields may be analyzed and which fields to index.

Once you’ve created your index, your can query it by using the methods above, replacing travel-search with the name you used to create the index.

To learn more about making your buckets searchable, see the Text Indexing section of the full text search documentation.

Query Types

The query executed in the previous section is called a string query. This type of query searches for terms based on a special type of input string. The query string +description:cheese -country:france will match documents which contain cheese in their description field, but are not located in France. String queries are ideal for searchbox fields to allow users to provide more specialized query criteria. You can read more about the Query String syntax in the full text search documentation.

There are many other query types available. These query types differ primarily in how they interpret the search term: whether it is treated as a phrase, a word, an exact match, or a prefix: A Match query searches for the input text within documents and is the simplest of queries. Match Phrase query searches for documents in which a specific phrase (i.e. one or more terms, such as "french cheese tasting") is present. A Prefix query searches documents which contain terms beginning with the supplied prefix.

There are some other specialized queries, such as Wildcard and Regexp queries which allow you to use wildcards (Couch?base') or regular expressions (Couchbase (php|python) SDK).

Below are two code snippets showing how the query for ch is treated differently when using a Prefix Query versus a Match Query.

results = cb.search('travel-search', FT.MatchQuery('ch'), limit=5)
for r in results:
    print('  Result: ID', r['id'])
    for location, terms in r['locations'].items():
        print('   ', location, terms.keys())
  Result: ID airline_1442
    iata dict_keys(['ch'])
  Result: ID landmark_35848
    image_direct_url dict_keys(['ch'])
results = cb.search('travel-search', FT.PrefixQuery('ch'), limit=5)
for r in results:
    print('  Result: ID', r['id'])
    for location, terms in r['locations'].items():
        print('   ', location, terms.keys())
  Result: ID hotel_15912
    reviews.content dict_keys(['check', 'cheese', 'charge', 'checkout', 'chairs', 'chances', 'choice', 'checked', 'cheapcaribbean', 'cheeses', 'charged', "church's", 'cheaper', 'chicken', 'change'])
    reviews.author dict_keys(['christiansen'])
  Result: ID hotel_33886
    reviews.content dict_keys(['check', 'chose', 'chips', 'choosing', 'chairs', 'channels', 'changed', 'choice', 'checked', 'chair', 'chocolate', 'chaise', 'checking', 'chicken', 'change', 'choose', 'charter', 'cheerful'])
    reviews.author dict_keys(['christy'])
  Result: ID hotel_16634
    reviews.content dict_keys(['check', 'chocolate', 'chinese', 'chairs', 'children', 'chips', 'chilis', 'chilly', 'checked', 'choice', 'chicago', 'childrens', "church's", 'cheaper', 'chicken', 'choose', 'christina', 'choices'])
  Result: ID hotel_37318
    reviews.content dict_keys(['check', 'choices', 'chairs', 'children', 'changed', 'choice', 'charge', 'challenging', 'chair', 'childrens', 'chicken', 'change', 'choose', 'chambermaid', 'chichen', 'child'])
    city dict_keys(['cheshire'])
  Result: ID hotel_21723
    reviews.content dict_keys(['check', 'chairs', 'cheesy', 'changed', 'checked', 'chair', 'charging', 'chaotic', 'charge', 'chapel', 'change', 'choose', 'children', 'cheep', 'chef', 'child'])
    content dict_keys(['cheapie'])
    public_likes dict_keys(['christop'])

As can be seen in the above examples, the Term assumes the search input is an actual term to search for (ch) and therefore rejects things such as chose, chairs and similar.

Compound Queries

You can compose queries made of other queries. You can use a Conjunction or Disjunction query which contains one or more queries that the document should match (a Disjunction query can be configured with the number of required subqueries that must be matched). You may also use a Boolean query that itself contains sub queries which should, must, and must not be matched.

Compound queries can be used to execute searches such as find any landmark containing "cheese" and also containing one of "wine" , "crackers" , or "old", but does not contain "lake" or "ocean":

Compound Query example
results = cb.search('travel-search',
            should=[FT.TermQuery('wine'), FT.TermQuery('crackers')],
            must_not=[FT.TermQuery('lake'), FT.TermQuery('ocean')]),

for r in results:
    print('ID', r['id'])
    for location, terms in r['locations'].items():
        print('\t{}: {}'.format(location, terms.keys()))
ID landmark_25779
	content: dict_keys(['cheese', 'crackers'])
ID landmark_7063
	content: dict_keys(['wine'])
	alt: dict_keys(['cheese'])
	name: dict_keys(['wine'])
ID landmark_16693
	content: dict_keys(['cheese', 'wine'])
ID landmark_27793
	content: dict_keys(['cheese', 'wine'])
ID landmark_40690
	content: dict_keys(['cheese', 'wine'])

When using compoound queries, you can modify any subquery’s boost setting to increase its relevance and scoring over other subqueries, affecting the ordering.

Other Query Types

There are other query types you can use, such as Date Range and Numeric Range queries which match documents matching a certain time span or value range. There are also debugging queries such as Term and Phrase queries which perform exact queries (without any analysis).

For a quick overview of all the available query types, see the Types of Queries section of the full text search documentation.

Query Options

You can specify query options to modify how the search term is treated. This section will enumerate some common query options and how they affect query results.

  • field: This option restricts searches to a given field. By default searches will be executed against all fields.

  • fuzziness: Sets the leniency of the matching algorithm. A higher fuzziness value may result in less relevant matches being considered

  • analyzer: Sets the analyzer to be used for the search term.

  • limit: Limits the number of search results to be returned.

  • skip: Start returning after this many results. This may be used in conjunction with limit to use pagination.

Search Results

After you have executed a search, you will be given a set of results, containing information about documents which match the query. In the raw JSON payload, the server returns an object with a hits property, which contains a search result.

The search result itself is a JSON object containing:

  • id: The document ID of the hit

  • score: How relevant the result is to the initial search query. Search results are always ordered by score, with highest-scored hits appearing first.

  • locations: A JSON object containing information about each match in the document. Its keys are document paths (in the N1QL sense) where matches may be found, and its values are arrays that contain the match location. The match location is a JSON object whose keys are the matched terms found, and whose values are locations:

    • start: The character offset at which the matched text begins

    • end: The character offset at which the matched text ends

    • pos: The word-position of the matched result. This indicates how far deep the match is, in respect to words. For example if the searched term was schema, and the matched text was: Ahout NoSQL schema organization, the pos would be 3, or the third word in the field.

To learn more about the response format used by the FTS service, see the Response Object Schema section of the full text search documentation. Couchbase SDKs may abstract some of the fields or provide wrapper methods around them.

Aggregation and Statistics (Facets)

You may perform search result aggregation and statistics using facets. Facets allow you to specify aggregation parameters in your query. When the query results are received, aggregation results are returned alongside the actual query hits.

You can use a Term Facet to count the number of times a specific term appears in the results

results = cb.search('beer-search', FT.MatchQuery('hops'), limit=5,
                    facets={'terms': FT.TermFacet('description', limit=5)})
for result in results:
    # handle results

{'field': 'description',
 'missing': 9,
 'other': 30725,
 'terms': [{'count': 782, 'term': 'hops'},
           {'count': 432, 'term': 'beer'},
           {'count': 365, 'term': 'ale'},
           {'count': 327, 'term': 'malt'},
           {'count': 130, 'term': 'hop'}],
 'total': 32761}

You can likewise use a Date Range Facet to count the number of results by their age, and Numeric Range Facet to count results using an arbitrary numeric range.

To learn more about facets, see the Search Facets section of the full text search documentation.

Partial Search Results

The FTS service splits the indexing data between several pindexes. Because of that, you may encounter situations where only a subset of the pindexes could provide results (eg. if some pindex nodes are not online...).

What happens in this case is that FTS returns a list of partial results, and notifies you that one or several errors also happened. You can inspect the errors, which will each correspond to an failing pindex, via the SDK. Of course, the partial results (the result from healthy pindexes) are still available through the usual methods in the SDK result representation.