class Length(expression, **extra) [source]
Accepts a single text field or expression and returns the number of characters the value has. If the expression is null, then the length will also be null.
Usage example:
>>> # Get the length of the name and goes_by fields
>>> from django.db.models.functions import Length
>>> Author.objects.create(name='Margaret Smith')
>>> author = Author.objects.annotate(
... name_length=Length('name'),
... goes_by_length=Length('goes_by')).get()
>>> print(author.name_length, author.goes_by_length)
(14, None)
It can also be registered as a transform. For example:
>>> from django.db.models import CharField >>> from django.db.models.functions import Length >>> CharField.register_lookup(Length, 'length') >>> # Get authors whose name is longer than 7 characters >>> authors = Author.objects.filter(name__length__gt=7)
Changed in Django 1.9:
The ability to register the function as a transform was added.
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