EdgeNgramField min and max letters in django haystack

Question

Is there a way to restrict the size of the edge ngrams in django haystack indexing? For example, I create the ngram as follows:

#search_indexes.py
content_auto = indexes.EdgeNgramField(model_attr='name')

But I don't want to create 2 letter ngrams, I actually want to set the min at 4 or 5.

As background, I am using django-haystack/elasticsearch, with bonsai on heroku.

Answer 1

What you need to do is override the search mapping in Haystack's ElasticSearch backend.

In brief: extend the ElasticSearch backend and either replace directly or by a settings.py import a new schema mapping.

from django.conf import settings
from haystack.backends.elasticsearch_backend import (ElasticsearchSearchBackend,
    ElasticsearchSearchEngine)

class MyElasticBackend(ElasticsearchSearchBackend):

    def __init__(self, connection_alias, **connection_options):
        super(ConfigurableElasticBackend, self).__init__(
                                connection_alias, **connection_options)
        MY_SETTINGS = {
            'settings': {
                "analysis": {
                    "analyzer": {
                        "ngram_analyzer": {
                            "type": "custom",
                            "tokenizer": "lowercase",
                            "filter": ["haystack_ngram"]
                        },
                        "edgengram_analyzer": {
                            "type": "custom",
                            "tokenizer": "lowercase",
                            "filter": ["haystack_edgengram"]
                        }
                    },
                    "tokenizer": {
                        "haystack_ngram_tokenizer": {
                            "type": "nGram",
                            "min_gram": 3,
                            "max_gram": 15,
                        },
                        "haystack_edgengram_tokenizer": {
                            "type": "edgeNGram",
                            "min_gram": 2,
                            "max_gram": 15,
                            "side": "front"
                        }
                    },
                    "filter": {
                        "haystack_ngram": {
                            "type": "nGram",
                            "min_gram": 3,
                            "max_gram": 15
                        },
                        "haystack_edgengram": {
                            "type": "edgeNGram",
                            "min_gram": 5,
                            "max_gram": 15
                        }
                    }
                }
            }
        }
        setattr(self, 'DEFAULT_SETTINGS', MY_SETTINGS)


class ConfigurableElasticSearchEngine(ElasticsearchSearchEngine):
    backend = MyElasticBackend

For a fuller explanation see my write up about extending the ElasticSearch backend to customize the search mapping.