# Τεκμηρίωση του Django - 1.10.7

# PostgreSQL specific lookups

## Trigram similarity

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>']

## `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>']

Προειδοποίηση

`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.