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Autocomplete

Autocomplete is becoming increasingly common as an add-on to search. Haystack makes it relatively simple to implement. There are two steps in the process, one to prepare the data and one to implement the actual search.

Step 1. Setup The Data

To do autocomplete effectively, the search backend uses n-grams (essentially a small window passed over the string). Because this alters the way your data needs to be stored, the best approach is to add a new field to your SearchIndex that contains the text you want to autocomplete on.

You have two choices: NgramField & EdgeNgramField. Though very similar, the choice of field is somewhat important.

  • If you're working with standard text, EdgeNgramField tokenizes on whitespace. This prevents incorrect matches when part of two different words are mashed together as one n-gram. This is what most users should use.
  • If you're working with Asian languages or want to be able to autocomplete across word boundaries, NgramField should be what you use.

Example (continuing from the tutorial):

import datetime
from haystack import indexes
from myapp.models import Note


class NoteIndex(indexes.SearchIndex, indexes.Indexable):
    text = indexes.CharField(document=True, use_template=True)
    author = indexes.CharField(model_attr='user')
    pub_date = indexes.DateTimeField(model_attr='pub_date')
    # We add this for autocomplete.
    content_auto = indexes.EdgeNgramField(model_attr='content')

    def get_model(self):
        return Note

    def index_queryset(self):
        """Used when the entire index for model is updated."""
        return Note.objects.filter(pub_date__lte=datetime.datetime.now())

As with all schema changes, you'll need to rebuild/update your index after making this change.

Step 2. Performing The Query

Haystack ships with a convenience method to perform most autocomplete searches. You simply provide a field & the query you wish to search on to the SearchQuerySet.autocomplete method. Given the previous example, an example search would look like:

from haystack.query import SearchQuerySet

SearchQuerySet().autocomplete(content_auto='old')
# Result match things like 'goldfish', 'cuckold' & 'older'.

The results from the SearchQuerySet.autocomplete method are full search results, just like any regular filter.

If you need more control over your results, you can use standard SearchQuerySet.filter calls. For instance:

from haystack.query import SearchQuerySet

sqs = SearchQuerySet().filter(content_auto=request.GET.get('q', ''))

This can also be extended to use SQ for more complex queries (and is what's being done under the hood in the SearchQuerySet.autocomplete method).

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