746 lines
27 KiB
Plaintext
746 lines
27 KiB
Plaintext
==================
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Database Functions
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==================
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.. module:: django.db.models.functions
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:synopsis: Database Functions
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The classes documented below provide a way for users to use functions provided
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by the underlying database as annotations, aggregations, or filters in Django.
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Functions are also :doc:`expressions <expressions>`, so they can be used and
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combined with other expressions like :ref:`aggregate functions
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<aggregation-functions>`.
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We'll be using the following model in examples of each function::
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class Author(models.Model):
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name = models.CharField(max_length=50)
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age = models.PositiveIntegerField(null=True, blank=True)
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alias = models.CharField(max_length=50, null=True, blank=True)
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goes_by = models.CharField(max_length=50, null=True, blank=True)
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We don't usually recommend allowing ``null=True`` for ``CharField`` since this
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allows the field to have two "empty values", but it's important for the
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``Coalesce`` example below.
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``Cast``
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========
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.. class:: Cast(expression, output_field)
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.. versionadded:: 1.10
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Forces the result type of ``expression`` to be the one from ``output_field``.
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Usage example::
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>>> from django.db.models import FloatField
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>>> from django.db.models.functions import Cast
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>>> Value.objects.create(integer=4)
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>>> value = Value.objects.annotate(as_float=Cast('integer', FloatField())).get()
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>>> print(value.as_float)
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4.0
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``Coalesce``
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============
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.. class:: Coalesce(*expressions, **extra)
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Accepts a list of at least two field names or expressions and returns the
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first non-null value (note that an empty string is not considered a null
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value). Each argument must be of a similar type, so mixing text and numbers
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will result in a database error.
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Usage examples::
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>>> # Get a screen name from least to most public
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>>> from django.db.models import Sum, Value as V
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>>> from django.db.models.functions import Coalesce
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>>> Author.objects.create(name='Margaret Smith', goes_by='Maggie')
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>>> author = Author.objects.annotate(
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... screen_name=Coalesce('alias', 'goes_by', 'name')).get()
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>>> print(author.screen_name)
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Maggie
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>>> # Prevent an aggregate Sum() from returning None
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>>> aggregated = Author.objects.aggregate(
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... combined_age=Coalesce(Sum('age'), V(0)),
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... combined_age_default=Sum('age'))
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>>> print(aggregated['combined_age'])
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0
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>>> print(aggregated['combined_age_default'])
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None
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.. warning::
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A Python value passed to ``Coalesce`` on MySQL may be converted to an
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incorrect type unless explicitly cast to the correct database type:
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>>> from django.db.models.expressions import RawSQL
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>>> from django.utils import timezone
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>>> now = timezone.now()
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>>> now_sql = RawSQL("cast(%s as datetime)", (now,))
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>>> Coalesce('updated', now_sql)
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``Concat``
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==========
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.. class:: Concat(*expressions, **extra)
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Accepts a list of at least two text fields or expressions and returns the
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concatenated text. Each argument must be of a text or char type. If you want
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to concatenate a ``TextField()`` with a ``CharField()``, then be sure to tell
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Django that the ``output_field`` should be a ``TextField()``. This is also
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required when concatenating a ``Value`` as in the example below.
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This function will never have a null result. On backends where a null argument
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results in the entire expression being null, Django will ensure that each null
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part is converted to an empty string first.
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Usage example::
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>>> # Get the display name as "name (goes_by)"
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>>> from django.db.models import CharField, Value as V
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>>> from django.db.models.functions import Concat
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>>> Author.objects.create(name='Margaret Smith', goes_by='Maggie')
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>>> author = Author.objects.annotate(
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... screen_name=Concat('name', V(' ('), 'goes_by', V(')'),
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... output_field=CharField())).get()
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>>> print(author.screen_name)
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Margaret Smith (Maggie)
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``Greatest``
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============
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.. class:: Greatest(*expressions, **extra)
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Accepts a list of at least two field names or expressions and returns the
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greatest value. Each argument must be of a similar type, so mixing text and
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numbers will result in a database error.
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Usage example::
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class Blog(models.Model):
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body = models.TextField()
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modified = models.DateTimeField(auto_now=True)
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class Comment(models.Model):
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body = models.TextField()
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modified = models.DateTimeField(auto_now=True)
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blog = models.ForeignKey(Blog, on_delete=models.CASCADE)
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>>> from django.db.models.functions import Greatest
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>>> blog = Blog.objects.create(body='Greatest is the best.')
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>>> comment = Comment.objects.create(body='No, Least is better.', blog=blog)
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>>> comments = Comment.objects.annotate(last_updated=Greatest('modified', 'blog__modified'))
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>>> annotated_comment = comments.get()
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``annotated_comment.last_updated`` will be the most recent of ``blog.modified``
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and ``comment.modified``.
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.. warning::
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The behavior of ``Greatest`` when one or more expression may be ``null``
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varies between databases:
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- PostgreSQL: ``Greatest`` will return the largest non-null expression,
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or ``null`` if all expressions are ``null``.
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- SQLite, Oracle, and MySQL: If any expression is ``null``, ``Greatest``
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will return ``null``.
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The PostgreSQL behavior can be emulated using ``Coalesce`` if you know
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a sensible minimum value to provide as a default.
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``Least``
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=========
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.. class:: Least(*expressions, **extra)
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Accepts a list of at least two field names or expressions and returns the
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least value. Each argument must be of a similar type, so mixing text and numbers
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will result in a database error.
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.. warning::
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The behavior of ``Least`` when one or more expression may be ``null``
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varies between databases:
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- PostgreSQL: ``Least`` will return the smallest non-null expression,
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or ``null`` if all expressions are ``null``.
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- SQLite, Oracle, and MySQL: If any expression is ``null``, ``Least``
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will return ``null``.
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The PostgreSQL behavior can be emulated using ``Coalesce`` if you know
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a sensible maximum value to provide as a default.
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``Length``
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==========
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.. class:: Length(expression, **extra)
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Accepts a single text field or expression and returns the number of characters
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the value has. If the expression is null, then the length will also be null.
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Usage example::
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>>> # Get the length of the name and goes_by fields
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>>> from django.db.models.functions import Length
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>>> Author.objects.create(name='Margaret Smith')
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>>> author = Author.objects.annotate(
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... name_length=Length('name'),
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... goes_by_length=Length('goes_by')).get()
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>>> print(author.name_length, author.goes_by_length)
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(14, None)
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It can also be registered as a transform. For example::
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>>> from django.db.models import CharField
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>>> from django.db.models.functions import Length
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>>> CharField.register_lookup(Length, 'length')
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>>> # Get authors whose name is longer than 7 characters
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>>> authors = Author.objects.filter(name__length__gt=7)
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``Lower``
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=========
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.. class:: Lower(expression, **extra)
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Accepts a single text field or expression and returns the lowercase
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representation.
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It can also be registered as a transform as described in :class:`Length`.
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Usage example::
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>>> from django.db.models.functions import Lower
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>>> Author.objects.create(name='Margaret Smith')
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>>> author = Author.objects.annotate(name_lower=Lower('name')).get()
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>>> print(author.name_lower)
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margaret smith
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``Now``
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=======
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.. class:: Now()
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Returns the database server's current date and time when the query is executed,
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typically using the SQL ``CURRENT_TIMESTAMP``.
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Usage example::
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>>> from django.db.models.functions import Now
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>>> Article.objects.filter(published__lte=Now())
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<QuerySet [<Article: How to Django>]>
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.. admonition:: PostgreSQL considerations
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On PostgreSQL, the SQL ``CURRENT_TIMESTAMP`` returns the time that the
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current transaction started. Therefore for cross-database compatibility,
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``Now()`` uses ``STATEMENT_TIMESTAMP`` instead. If you need the transaction
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timestamp, use :class:`django.contrib.postgres.functions.TransactionNow`.
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``Substr``
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==========
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.. class:: Substr(expression, pos, length=None, **extra)
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Returns a substring of length ``length`` from the field or expression starting
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at position ``pos``. The position is 1-indexed, so the position must be greater
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than 0. If ``length`` is ``None``, then the rest of the string will be returned.
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Usage example::
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>>> # Set the alias to the first 5 characters of the name as lowercase
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>>> from django.db.models.functions import Substr, Lower
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>>> Author.objects.create(name='Margaret Smith')
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>>> Author.objects.update(alias=Lower(Substr('name', 1, 5)))
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1
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>>> print(Author.objects.get(name='Margaret Smith').alias)
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marga
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``Upper``
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=========
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.. class:: Upper(expression, **extra)
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Accepts a single text field or expression and returns the uppercase
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representation.
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It can also be registered as a transform as described in :class:`Length`.
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Usage example::
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>>> from django.db.models.functions import Upper
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>>> Author.objects.create(name='Margaret Smith')
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>>> author = Author.objects.annotate(name_upper=Upper('name')).get()
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>>> print(author.name_upper)
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MARGARET SMITH
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Date Functions
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==============
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.. module:: django.db.models.functions.datetime
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.. versionadded:: 1.10
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We'll be using the following model in examples of each function::
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class Experiment(models.Model):
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start_datetime = models.DateTimeField()
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start_date = models.DateField(null=True, blank=True)
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start_time = models.TimeField(null=True, blank=True)
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end_datetime = models.DateTimeField(null=True, blank=True)
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end_date = models.DateField(null=True, blank=True)
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end_time = models.TimeField(null=True, blank=True)
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``Extract``
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-----------
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.. class:: Extract(expression, lookup_name=None, tzinfo=None, **extra)
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Extracts a component of a date as a number.
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Takes an ``expression`` representing a ``DateField`` or ``DateTimeField`` and a
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``lookup_name``, and returns the part of the date referenced by ``lookup_name``
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as an ``IntegerField``. Django usually uses the databases' extract function, so
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you may use any ``lookup_name`` that your database supports. A ``tzinfo``
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subclass, usually provided by ``pytz``, can be passed to extract a value in a
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specific timezone.
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Given the datetime ``2015-06-15 23:30:01.000321+00:00``, the built-in
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``lookup_name``\s return:
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* "year": 2015
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* "month": 6
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* "day": 15
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* "week_day": 2
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* "hour": 23
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* "minute": 30
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* "second": 1
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If a different timezone like ``Australia/Melbourne`` is active in Django, then
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the datetime is converted to the timezone before the value is extracted. The
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timezone offset for Melbourne in the example date above is +10:00. The values
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returned when this timezone is active will be the same as above except for:
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* "day": 16
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* "week_day": 3
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* "hour": 9
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.. admonition:: ``week_day`` values
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The ``week_day`` ``lookup_type`` is calculated differently from most
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databases and from Python's standard functions. This function will return
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``1`` for Sunday, ``2`` for Monday, through ``7`` for Saturday.
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The equivalent calculation in Python is::
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>>> from datetime import datetime
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>>> dt = datetime(2015, 6, 15)
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>>> (dt.isoweekday() % 7) + 1
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2
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Each ``lookup_name`` above has a corresponding ``Extract`` subclass (listed
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below) that should typically be used instead of the more verbose equivalent,
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e.g. use ``ExtractYear(...)`` rather than ``Extract(..., lookup_name='year')``.
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Usage example::
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>>> from datetime import datetime
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>>> from django.db.models.functions import Extract
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>>> start = datetime(2015, 6, 15)
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>>> end = datetime(2015, 7, 2)
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>>> Experiment.objects.create(
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... start_datetime=start, start_date=start.date(),
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... end_datetime=end, end_date=end.date())
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>>> # Add the experiment start year as a field in the QuerySet.
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>>> experiment = Experiment.objects.annotate(
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... start_year=Extract('start_datetime', 'year')).get()
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>>> experiment.start_year
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2015
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>>> # How many experiments completed in the same year in which they started?
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>>> Experiment.objects.filter(
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... start_datetime__year=Extract('end_datetime', 'year')).count()
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1
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``DateField`` extracts
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~~~~~~~~~~~~~~~~~~~~~~
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.. class:: ExtractYear(expression, tzinfo=None, **extra)
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.. attribute:: lookup_name = 'year'
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.. class:: ExtractMonth(expression, tzinfo=None, **extra)
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.. attribute:: lookup_name = 'month'
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.. class:: ExtractDay(expression, tzinfo=None, **extra)
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.. attribute:: lookup_name = 'day'
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.. class:: ExtractWeekDay(expression, tzinfo=None, **extra)
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.. attribute:: lookup_name = 'week_day'
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These are logically equivalent to ``Extract('date_field', lookup_name)``. Each
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class is also a ``Transform`` registered on ``DateField`` and ``DateTimeField``
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as ``__(lookup_name)``, e.g. ``__year``.
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Since ``DateField``\s don't have a time component, only ``Extract`` subclasses
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that deal with date-parts can be used with ``DateField``::
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>>> from datetime import datetime
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>>> from django.utils import timezone
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>>> from django.db.models.functions import (
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... ExtractYear, ExtractMonth, ExtractDay, ExtractWeekDay
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... )
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>>> start_2015 = datetime(2015, 6, 15, 23, 30, 1, tzinfo=timezone.utc)
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>>> end_2015 = datetime(2015, 6, 16, 13, 11, 27, tzinfo=timezone.utc)
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>>> Experiment.objects.create(
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... start_datetime=start_2015, start_date=start_2015.date(),
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... end_datetime=end_2015, end_date=end_2015.date())
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>>> Experiment.objects.annotate(
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... year=ExtractYear('start_date'),
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... month=ExtractMonth('start_date'),
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... day=ExtractDay('start_date'),
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... weekday=ExtractWeekDay('start_date'),
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... ).values('year', 'month', 'day', 'weekday').get(
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... end_date__year=ExtractYear('start_date'),
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... )
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{'year': 2015, 'month': 6, 'day': 15, 'weekday': 2}
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``DateTimeField`` extracts
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~~~~~~~~~~~~~~~~~~~~~~~~~~
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In addition to the following, all extracts for ``DateField`` listed above may
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also be used on ``DateTimeField``\s .
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.. class:: ExtractHour(expression, tzinfo=None, **extra)
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.. attribute:: lookup_name = 'hour'
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.. class:: ExtractMinute(expression, tzinfo=None, **extra)
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.. attribute:: lookup_name = 'minute'
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.. class:: ExtractSecond(expression, tzinfo=None, **extra)
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.. attribute:: lookup_name = 'second'
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These are logically equivalent to ``Extract('datetime_field', lookup_name)``.
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Each class is also a ``Transform`` registered on ``DateTimeField`` as
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``__(lookup_name)``, e.g. ``__minute``.
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``DateTimeField`` examples::
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>>> from datetime import datetime
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>>> from django.utils import timezone
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>>> from django.db.models.functions import (
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... ExtractYear, ExtractMonth, ExtractDay, ExtractWeekDay,
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... ExtractHour, ExtractMinute, ExtractSecond,
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... )
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>>> start_2015 = datetime(2015, 6, 15, 23, 30, 1, tzinfo=timezone.utc)
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>>> end_2015 = datetime(2015, 6, 16, 13, 11, 27, tzinfo=timezone.utc)
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>>> Experiment.objects.create(
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... start_datetime=start_2015, start_date=start_2015.date(),
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... end_datetime=end_2015, end_date=end_2015.date())
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>>> Experiment.objects.annotate(
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... year=ExtractYear('start_datetime'),
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... month=ExtractMonth('start_datetime'),
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... day=ExtractDay('start_datetime'),
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... weekday=ExtractWeekDay('start_datetime'),
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... hour=ExtractHour('start_datetime'),
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... minute=ExtractMinute('start_datetime'),
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... second=ExtractSecond('start_datetime'),
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... ).values(
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... 'year', 'month', 'day', 'weekday', 'hour', 'minute', 'second',
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... ).get(end_datetime__year=ExtractYear('start_datetime'))
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{'year': 2015, 'month': 6, 'day': 15, 'weekday': 2, 'hour': 23, 'minute': 30, 'second': 1}
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When :setting:`USE_TZ` is ``True`` then datetimes are stored in the database
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in UTC. If a different timezone is active in Django, the datetime is converted
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to that timezone before the value is extracted. The example below converts to
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the Melbourne timezone (UTC +10:00), which changes the day, weekday, and hour
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values that are returned::
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>>> import pytz
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>>> tzinfo = pytz.timezone('Australia/Melbourne') # UTC+10:00
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>>> with timezone.override(tzinfo):
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... Experiment.objects.annotate(
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... day=ExtractDay('start_datetime'),
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... weekday=ExtractWeekDay('start_datetime'),
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... hour=ExtractHour('start_datetime'),
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... ).values('day', 'weekday', 'hour').get(
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... end_datetime__year=ExtractYear('start_datetime'),
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... )
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{'day': 16, 'weekday': 3, 'hour': 9}
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Explicitly passing the timezone to the ``Extract`` function behaves in the same
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way, and takes priority over an active timezone::
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>>> import pytz
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>>> tzinfo = pytz.timezone('Australia/Melbourne')
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>>> Experiment.objects.annotate(
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... day=ExtractDay('start_datetime', tzinfo=melb),
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... weekday=ExtractWeekDay('start_datetime', tzinfo=melb),
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... hour=ExtractHour('start_datetime', tzinfo=melb),
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... ).values('day', 'weekday', 'hour').get(
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... end_datetime__year=ExtractYear('start_datetime'),
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... )
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{'day': 16, 'weekday': 3, 'hour': 9}
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``Trunc``
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---------
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.. class:: Trunc(expression, kind, output_field=None, tzinfo=None, **extra)
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Truncates a date up to a significant component.
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When you only care if something happened in a particular year, hour, or day,
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but not the exact second, then ``Trunc`` (and its subclasses) can be useful to
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filter or aggregate your data. For example, you can use ``Trunc`` to calculate
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the number of sales per day.
|
|
|
|
``Trunc`` takes a single ``expression``, representing a ``DateField``,
|
|
``TimeField``, or ``DateTimeField``, a ``kind`` representing a date or time
|
|
part, and an ``output_field`` that's either ``DateTimeField()``,
|
|
``TimeField()``, or ``DateField()``. It returns a datetime, date, or time
|
|
depending on ``output_field``, with fields up to ``kind`` set to their minimum
|
|
value. If ``output_field`` is omitted, it will default to the ``output_field``
|
|
of ``expression``. A ``tzinfo`` subclass, usually provided by ``pytz``, can be
|
|
passed to truncate a value in a specific timezone.
|
|
|
|
Given the datetime ``2015-06-15 14:30:50.000321+00:00``, the built-in ``kind``\s
|
|
return:
|
|
|
|
* "year": 2015-01-01 00:00:00+00:00
|
|
* "month": 2015-06-01 00:00:00+00:00
|
|
* "day": 2015-06-15 00:00:00+00:00
|
|
* "hour": 2015-06-15 14:00:00+00:00
|
|
* "minute": 2015-06-15 14:30:00+00:00
|
|
* "second": 2015-06-15 14:30:50+00:00
|
|
|
|
If a different timezone like ``Australia/Melbourne`` is active in Django, then
|
|
the datetime is converted to the new timezone before the value is truncated.
|
|
The timezone offset for Melbourne in the example date above is +10:00. The
|
|
values returned when this timezone is active will be:
|
|
|
|
* "year": 2015-01-01 00:00:00+11:00
|
|
* "month": 2015-06-01 00:00:00+10:00
|
|
* "day": 2015-06-16 00:00:00+10:00
|
|
* "hour": 2015-06-16 00:00:00+10:00
|
|
* "minute": 2015-06-16 00:30:00+10:00
|
|
* "second": 2015-06-16 00:30:50+10:00
|
|
|
|
The year has an offset of +11:00 because the result transitioned into daylight
|
|
saving time.
|
|
|
|
Each ``kind`` above has a corresponding ``Trunc`` subclass (listed below) that
|
|
should typically be used instead of the more verbose equivalent,
|
|
e.g. use ``TruncYear(...)`` rather than ``Trunc(..., kind='year')``.
|
|
|
|
The subclasses are all defined as transforms, but they aren't registered with
|
|
any fields, because the obvious lookup names are already reserved by the
|
|
``Extract`` subclasses.
|
|
|
|
Usage example::
|
|
|
|
>>> from datetime import datetime
|
|
>>> from django.db.models import Count, DateTimeField
|
|
>>> from django.db.models.functions import Trunc
|
|
>>> Experiment.objects.create(start_datetime=datetime(2015, 6, 15, 14, 30, 50, 321))
|
|
>>> Experiment.objects.create(start_datetime=datetime(2015, 6, 15, 14, 40, 2, 123))
|
|
>>> Experiment.objects.create(start_datetime=datetime(2015, 12, 25, 10, 5, 27, 999))
|
|
>>> experiments_per_day = Experiment.objects.annotate(
|
|
... start_day=Trunc('start_datetime', 'day', output_field=DateTimeField())
|
|
... ).values('start_day').annotate(experiments=Count('id'))
|
|
>>> for exp in experiments_per_day:
|
|
... print(exp['start_day'], exp['experiments'])
|
|
...
|
|
2015-06-15 00:00:00 2
|
|
2015-12-25 00:00:00 1
|
|
>>> experiments = Experiment.objects.annotate(
|
|
... start_day=Trunc('start_datetime', 'day', output_field=DateTimeField())
|
|
... ).filter(start_day=datetime(2015, 6, 15))
|
|
>>> for exp in experiments:
|
|
... print(exp.start_datetime)
|
|
...
|
|
2015-06-15 14:30:50.000321
|
|
2015-06-15 14:40:02.000123
|
|
|
|
``DateField`` truncation
|
|
~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
.. class:: TruncYear(expression, output_field=None, tzinfo=None, **extra)
|
|
|
|
.. attribute:: kind = 'year'
|
|
|
|
.. class:: TruncMonth(expression, output_field=None, tzinfo=None, **extra)
|
|
|
|
.. attribute:: kind = 'month'
|
|
|
|
These are logically equivalent to ``Trunc('date_field', kind)``. They truncate
|
|
all parts of the date up to ``kind`` which allows grouping or filtering dates
|
|
with less precision. ``expression`` can have an ``output_field`` of either
|
|
``DateField`` or ``DateTimeField``.
|
|
|
|
Since ``DateField``\s don't have a time component, only ``Trunc`` subclasses
|
|
that deal with date-parts can be used with ``DateField``::
|
|
|
|
>>> from datetime import datetime
|
|
>>> from django.db.models import Count
|
|
>>> from django.db.models.functions import TruncMonth, TruncYear
|
|
>>> from django.utils import timezone
|
|
>>> start1 = datetime(2014, 6, 15, 14, 30, 50, 321, tzinfo=timezone.utc)
|
|
>>> start2 = datetime(2015, 6, 15, 14, 40, 2, 123, tzinfo=timezone.utc)
|
|
>>> start3 = datetime(2015, 12, 31, 17, 5, 27, 999, tzinfo=timezone.utc)
|
|
>>> Experiment.objects.create(start_datetime=start1, start_date=start1.date())
|
|
>>> Experiment.objects.create(start_datetime=start2, start_date=start2.date())
|
|
>>> Experiment.objects.create(start_datetime=start3, start_date=start3.date())
|
|
>>> experiments_per_year = Experiment.objects.annotate(
|
|
... year=TruncYear('start_date')).values('year').annotate(
|
|
... experiments=Count('id'))
|
|
>>> for exp in experiments_per_year:
|
|
... print(exp['year'], exp['experiments'])
|
|
...
|
|
2014-01-01 1
|
|
2015-01-01 2
|
|
|
|
>>> import pytz
|
|
>>> melb = pytz.timezone('Australia/Melbourne')
|
|
>>> experiments_per_month = Experiment.objects.annotate(
|
|
... month=TruncMonth('start_datetime', tzinfo=melb)).values('month').annotate(
|
|
... experiments=Count('id'))
|
|
>>> for exp in experiments_per_month:
|
|
... print(exp['month'], exp['experiments'])
|
|
...
|
|
2015-06-01 00:00:00+10:00 1
|
|
2016-01-01 00:00:00+11:00 1
|
|
2014-06-01 00:00:00+10:00 1
|
|
|
|
``TimeField`` truncation
|
|
~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
.. versionadded:: 1.11
|
|
|
|
.. class:: TruncHour(expression, output_field=None, tzinfo=None, **extra)
|
|
|
|
.. attribute:: kind = 'hour'
|
|
|
|
.. class:: TruncMinute(expression, output_field=None, tzinfo=None, **extra)
|
|
|
|
.. attribute:: kind = 'minute'
|
|
|
|
.. class:: TruncSecond(expression, output_field=None, tzinfo=None, **extra)
|
|
|
|
.. attribute:: kind = 'second'
|
|
|
|
These are logically equivalent to ``Trunc('time_field', kind)``. They truncate
|
|
all parts of the time up to ``kind`` which allows grouping or filtering times
|
|
with less precision. ``expression`` can have an ``output_field`` of either
|
|
``TimeField`` or ``DateTimeField``.
|
|
|
|
Since ``TimeField``\s don't have a date component, only ``Trunc`` subclasses
|
|
that deal with time-parts can be used with ``TimeField``::
|
|
|
|
>>> from datetime import datetime
|
|
>>> from django.db.models import Count, TimeField
|
|
>>> from django.db.models.functions import TruncHour
|
|
>>> from django.utils import timezone
|
|
>>> start1 = datetime(2014, 6, 15, 14, 30, 50, 321, tzinfo=timezone.utc)
|
|
>>> start2 = datetime(2014, 6, 15, 14, 40, 2, 123, tzinfo=timezone.utc)
|
|
>>> start3 = datetime(2015, 12, 31, 17, 5, 27, 999, tzinfo=timezone.utc)
|
|
>>> Experiment.objects.create(start_datetime=start1, start_time=start1.time())
|
|
>>> Experiment.objects.create(start_datetime=start2, start_time=start2.time())
|
|
>>> Experiment.objects.create(start_datetime=start3, start_time=start3.time())
|
|
>>> experiments_per_hour = Experiment.objects.annotate(
|
|
... hour=TruncHour('start_datetime', output_field=TimeField()),
|
|
... ).values('hour').annotate(experiments=Count('id'))
|
|
>>> for exp in experiments_per_hour:
|
|
... print(exp['hour'], exp['experiments'])
|
|
...
|
|
14:00:00 2
|
|
17:00:00 1
|
|
|
|
>>> import pytz
|
|
>>> melb = pytz.timezone('Australia/Melbourne')
|
|
>>> experiments_per_hour = Experiment.objects.annotate(
|
|
... hour=TruncHour('start_datetime', tzinfo=melb),
|
|
... ).values('hour').annotate(experiments=Count('id'))
|
|
>>> for exp in experiments_per_hour:
|
|
... print(exp['hour'], exp['experiments'])
|
|
...
|
|
2014-06-16 00:00:00+10:00 2
|
|
2016-01-01 04:00:00+11:00 1
|
|
|
|
``DateTimeField`` truncation
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
.. class:: TruncDate(expression, **extra)
|
|
|
|
.. attribute:: lookup_name = 'date'
|
|
.. attribute:: output_field = DateField()
|
|
|
|
``TruncDate`` casts ``expression`` to a date rather than using the built-in SQL
|
|
truncate function. It's also registered as a transform on ``DateTimeField`` as
|
|
``__date``.
|
|
|
|
.. class:: TruncTime(expression, **extra)
|
|
|
|
.. versionadded:: 1.11
|
|
|
|
.. attribute:: lookup_name = 'time'
|
|
.. attribute:: output_field = TimeField()
|
|
|
|
``TruncTime`` casts ``expression`` to a time rather than using the built-in SQL
|
|
truncate function. It's also registered as a transform on ``DateTimeField`` as
|
|
``__time``.
|
|
|
|
.. class:: TruncDay(expression, output_field=None, tzinfo=None, **extra)
|
|
|
|
.. attribute:: kind = 'day'
|
|
|
|
.. class:: TruncHour(expression, output_field=None, tzinfo=None, **extra)
|
|
|
|
.. attribute:: kind = 'hour'
|
|
|
|
.. class:: TruncMinute(expression, output_field=None, tzinfo=None, **extra)
|
|
|
|
.. attribute:: kind = 'minute'
|
|
|
|
.. class:: TruncSecond(expression, output_field=None, tzinfo=None, **extra)
|
|
|
|
.. attribute:: kind = 'second'
|
|
|
|
These are logically equivalent to ``Trunc('datetime_field', kind)``. They
|
|
truncate all parts of the date up to ``kind`` and allow grouping or filtering
|
|
datetimes with less precision. ``expression`` must have an ``output_field`` of
|
|
``DateTimeField``.
|
|
|
|
Usage example::
|
|
|
|
>>> from datetime import date, datetime
|
|
>>> from django.db.models import Count
|
|
>>> from django.db.models.functions import (
|
|
... TruncDate, TruncDay, TruncHour, TruncMinute, TruncSecond,
|
|
... )
|
|
>>> from django.utils import timezone
|
|
>>> import pytz
|
|
>>> start1 = datetime(2014, 6, 15, 14, 30, 50, 321, tzinfo=timezone.utc)
|
|
>>> Experiment.objects.create(start_datetime=start1, start_date=start1.date())
|
|
>>> melb = pytz.timezone('Australia/Melbourne')
|
|
>>> Experiment.objects.annotate(
|
|
... date=TruncDate('start_datetime'),
|
|
... day=TruncDay('start_datetime', tzinfo=melb),
|
|
... hour=TruncHour('start_datetime', tzinfo=melb),
|
|
... minute=TruncMinute('start_datetime'),
|
|
... second=TruncSecond('start_datetime'),
|
|
... ).values('date', 'day', 'hour', 'minute', 'second').get()
|
|
{'date': datetime.date(2014, 6, 15),
|
|
'day': datetime.datetime(2014, 6, 16, 0, 0, tzinfo=<DstTzInfo 'Australia/Melbourne' AEST+10:00:00 STD>),
|
|
'hour': datetime.datetime(2014, 6, 16, 0, 0, tzinfo=<DstTzInfo 'Australia/Melbourne' AEST+10:00:00 STD>),
|
|
'minute': 'minute': datetime.datetime(2014, 6, 15, 14, 30, tzinfo=<UTC>),
|
|
'second': datetime.datetime(2014, 6, 15, 14, 30, 50, tzinfo=<UTC>)
|
|
}
|