PostgreSQL specific lookups¶
Trigram similarity¶
trigram_similar¶
The trigram_similar lookup allows you to perform trigram lookups,
measuring the number of trigrams (three consecutive characters) shared, using a
dedicated PostgreSQL extension. A trigram lookup is given an expression and
returns results that have a similarity measurement greater than the current
similarity threshold.
To use it, add 'django.contrib.postgres' in your INSTALLED_APPS
and activate the pg_trgm extension on PostgreSQL. You can install the
extension using the
TrigramExtension migration
operation.
The trigram_similar lookup can be used on
CharField and TextField:
>>> City.objects.filter(name__trigram_similar="Middlesborough")
['<City: Middlesbrough>']
trigram_word_similar¶
The trigram_word_similar lookup allows you to perform trigram word
similarity lookups using a dedicated PostgreSQL extension. It can be
approximately understood as measuring the greatest number of trigrams shared
between the parameter and any substring of the field. A trigram word lookup is
given an expression and returns results that have a word similarity measurement
greater than the current similarity threshold.
To use it, add 'django.contrib.postgres' in your INSTALLED_APPS
and activate the pg_trgm extension on PostgreSQL. You can install the
extension using the
TrigramExtension migration
operation.
The trigram_word_similar lookup can be used on
CharField and TextField:
>>> Sentence.objects.filter(name__trigram_word_similar="Middlesborough")
['<Sentence: Gumby rides on the path of Middlesbrough>']
trigram_strict_word_similar¶
Similar to trigram_word_similar, except that it forces extent
boundaries to match word boundaries.
To use it, add 'django.contrib.postgres' in your INSTALLED_APPS
and activate the pg_trgm extension on PostgreSQL. You can install the
extension using the
TrigramExtension migration
operation.
The trigram_strict_word_similar lookup can be used on
CharField and TextField.
Unaccent¶
The unaccent lookup allows you to perform accent-insensitive lookups using
a dedicated PostgreSQL extension.
This lookup is implemented using Transform, so it
can be chained with other lookup functions. To use it, you need to add
'django.contrib.postgres' in your INSTALLED_APPS and activate
the unaccent extension on PostgreSQL. The
UnaccentExtension migration
operation is available if you want to perform this activation using migrations).
The unaccent lookup can be used on
CharField and TextField:
>>> City.objects.filter(name__unaccent="México")
['<City: Mexico>']
>>> User.objects.filter(first_name__unaccent__startswith="Jerem")
['<User: Jeremy>', '<User: Jérémy>', '<User: Jérémie>', '<User: Jeremie>']
Aviso
unaccent lookups should perform fine in most use cases. However, queries
using this filter will generally perform full table scans, which can be slow
on large tables. In those cases, using dedicated full text indexing tools
might be appropriate.
