Fixed #24767 -- Added Greatest and Least expressions (4ab53a55) · Commits · Dom Sekotill / django

django/db/backends/base/features.py

+4 −0

Original line number	Diff line number	Diff line
		@@ -208,6 +208,10 @@ class BaseDatabaseFeatures(object):
		# Does the backend support "select for update" queries with limit (and offset)?
		supports_select_for_update_with_limit = True

		# Does the backend ignore null expressions in GREATEST and LEAST queries unless
		# every expression is null?
		greatest_least_ignores_nulls = False

		def __init__(self, connection):
		self.connection = connection

django/db/backends/postgresql_psycopg2/features.py

+1 −0

Original line number	Diff line number	Diff line
		@@ -27,3 +27,4 @@ class DatabaseFeatures(BaseDatabaseFeatures):
		closed_cursor_error_class = InterfaceError
		has_case_insensitive_like = False
		requires_sqlparse_for_splitting = False
		greatest_least_ignores_nulls = True

django/db/models/functions.py

+42 −0

Original line number	Diff line number	Diff line
		@@ -83,6 +83,48 @@ class Concat(Func):
		return ConcatPair(expressions[0], self._paired(expressions[1:]))


		class Greatest(Func):
		"""
		Chooses the maximum expression and returns it.

		If any expression is null the return value is database-specific:
		On Postgres, the maximum not-null expression is returned.
		On MySQL, Oracle and SQLite, if any expression is null, null is
		returned.
		"""
		function = 'GREATEST'

		def __init__(self, expressions, *extra):
		if len(expressions) < 2:
		raise ValueError('Greatest must take at least two expressions')
		super(Greatest, self).__init__(expressions, *extra)

		def as_sqlite(self, compiler, connection):
		"""Use the MAX function on SQLite."""
		return super(Greatest, self).as_sql(compiler, connection, function='MAX')


		class Least(Func):
		"""
		Chooses the minimum expression and returns it.

		If any expression is null the return value is database-specific:
		On Postgres, the minimum not-null expression is returned.
		On MySQL, Oracle and SQLite, if any expression is null, null is
		returned.
		"""
		function = 'LEAST'

		def __init__(self, expressions, *extra):
		if len(expressions) < 2:
		raise ValueError('Least must take at least two expressions')
		super(Least, self).__init__(expressions, *extra)

		def as_sqlite(self, compiler, connection):
		"""Use the MIN function on SQLite."""
		return super(Least, self).as_sql(compiler, connection, function='MIN')


		class Length(Func):
		"""Returns the number of characters in the expression"""
		function = 'LENGTH'

docs/ref/models/database-functions.txt

+68 −0

Original line number	Diff line number	Diff line
		@@ -82,6 +82,74 @@ Usage example::
		>>> print(author.screen_name)
		Margaret Smith (Maggie)

		Greatest
		--------

		.. versionadded:: 1.9

		.. class:: Greatest(expressions, *extra)

		Accepts a list of at least two field names or expressions and returns the
		greatest value. Each argument must be of a similar type, so mixing text and numbers
		will result in a database error.

		Usage example::

		class Blog(models.Model):
		body = models.TextField()
		modified = models.DateTimeField(auto_now=True)

		class Comment(models.Model):
		body = models.TextField()
		modified = models.DateTimeField(auto_now=True)
		blog = models.ForeignKey(Blog)

		>>> from django.db.models.functions import Greatest
		>>> blog = Blog.objects.create(body='Greatest is the best.')
		>>> comment = Comment.objects.create(body='No, Least is better.', blog=blog)
		>>> comments = Comment.objects.annotate(last_updated=Greatest('modified', 'blog__modified'))
		>>> annotated_comment = comments.get()

		``annotated_comment.last_updated`` will be the most recent of
		``blog.modified`` and ``comment.modified``.

		.. warning::

		The behavior of ``Greatest`` when one or more expression may be ``null``
		varies between databases:

		- PostgreSQL: ``Greatest`` will return the largest non-null expression,
		or ``null`` if all expressions are ``null``.
		- SQLite, Oracle and MySQL: If any expression is ``null``, ``Greatest``
		will return ``null``.

		The PostgreSQL behavior can be emulated using ``Coalesce`` if you know
		a sensible minimum value to provide as a default.

		Least
		--------

		.. versionadded:: 1.9

		.. class:: Least(expressions, *extra)

		Accepts a list of at least two field names or expressions and returns the
		least value. Each argument must be of a similar type, so mixing text and numbers
		will result in a database error.

		.. warning::

		The behavior of ``Least`` when one or more expression may be ``null``
		varies between databases:

		- PostgreSQL: ``Least`` will return the smallest non-null expression,
		or ``null`` if all expressions are ``null``.
		- SQLite, Oracle and MySQL: If any expression is ``null``, ``Least``
		will return ``null``.

		The PostgreSQL behavior can be emulated using ``Coalesce`` if you know
		a sensible maximum value to provide as a default.

		Length
		------

docs/releases/1.9.txt

+3 −0

Original line number	Diff line number	Diff line
		@@ -256,6 +256,9 @@ Models
		* Added the :lookup:`date` lookup to :class:`~django.db.models.DateTimeField`
		to allow querying the field by only the date portion.

		* Added the :class:`~django.db.models.functions.Greatest` and
		:class:`~django.db.models.functions.Least` database functions.

		* Added the :class:`~django.db.models.functions.Now` database function, which
		returns the current date and time.