class Coalesce(*expressions, **extra) [source]
Accepts a list of at least two field names or expressions and returns the first non-null value (note that an empty string is not considered a null value). Each argument must be of a similar type, so mixing text and numbers will result in a database error.
Usage examples:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | >>> # Get a screen name from least to most public>>> from django.db.models import Sum, Value as V>>> from django.db.models.functions import Coalesce>>> Author.objects.create(name='Margaret Smith', goes_by='Maggie')>>> author = Author.objects.annotate(... screen_name=Coalesce('alias', 'goes_by', 'name')).get()>>> print(author.screen_name)Maggie>>> # Prevent an aggregate Sum() from returning None>>> aggregated = Author.objects.aggregate(... combined_age=Coalesce(Sum('age'), V(0)),... combined_age_default=Sum('age'))>>> print(aggregated['combined_age'])0>>> print(aggregated['combined_age_default'])None |
Warning
A Python value passed to Coalesce on MySQL may be converted to an incorrect type unless explicitly cast to the correct database type:
1 2 3 4 5 | >>> from django.db.models.expressions import RawSQL>>> from django.utils import timezone>>> now = timezone.now()>>> now_sql = RawSQL("cast(%s as datetime)", (now,))>>> Coalesce('updated', now_sql) |
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