Commit 03b69477 authored by Claude Paroz's avatar Claude Paroz Committed by Tim Graham
Browse files

Fixed #24932 -- Added Cast database function. 

Thanks Ian Foote for the initial patch.
parent 53361589

django/db/models/functions.py

+33 −0
Original line number Diff line number Diff line
@@ -4,6 +4,39 @@ Classes that represent database functions. 
from django.db.models import Func, Transform, Value, fields





class Cast(Func):

    """

    Coerce an expression to a new field type.

    """

    function = 'CAST'

    template = '%(function)s(%(expressions)s AS %(db_type)s)'



    mysql_types = {

        fields.CharField: 'char',

        fields.IntegerField: 'signed integer',

        fields.FloatField: 'signed',

    }



    def __init__(self, expression, output_field):

        super(Cast, self).__init__(expression, output_field=output_field)



    def as_sql(self, compiler, connection, **extra_context):

        if 'db_type' not in extra_context:

            extra_context['db_type'] = self._output_field.db_type(connection)

        return super(Cast, self).as_sql(compiler, connection, **extra_context)



    def as_mysql(self, compiler, connection):

        extra_context = {}

        output_field_class = type(self._output_field)

        if output_field_class in self.mysql_types:

            extra_context['db_type'] = self.mysql_types[output_field_class]

        return self.as_sql(compiler, connection, **extra_context)



    def as_postgresql(self, compiler, connection):

        # CAST would be valid too, but the :: shortcut syntax is more readable.

        return self.as_sql(compiler, connection, template='%(expressions)s::%(db_type)s')





class Coalesce(Func):

    """

    Chooses, from left to right, the first non-null expression and returns it.

docs/ref/models/database-functions.txt

+18 −0
Original line number Diff line number Diff line
@@ -23,6 +23,24 @@ We don't usually recommend allowing ``null=True`` for ``CharField`` since this 
allows the field to have two "empty values", but it's important for the

``Coalesce`` example below.



``Cast``

========



.. class:: Cast(expression, output_field)



.. versionadded:: 1.10



Forces the result type of ``expression`` to be the one from ``output_field``.



Usage example::



    >>> from django.db.models import FloatField

    >>> from django.db.models.functions import Cast

    >>> Value.objects.create(integer=4)

    >>> value = Value.objects.annotate(as_float=Cast('integer', FloatField)).get()

    >>> print(value.as_float)

    4.0



``Coalesce``

============

docs/releases/1.10.txt

+2 −0
Original line number Diff line number Diff line
@@ -349,6 +349,8 @@ Models 
* :meth:`QuerySet.bulk_create() <django.db.models.query.QuerySet.bulk_create>`

  sets the primary key on objects when using PostgreSQL.



* Added the :class:`~django.db.models.functions.Cast` database function.



Requests and Responses

~~~~~~~~~~~~~~~~~~~~~~

tests/db_functions/test_cast.py

0 → 100644
+24 −0
Original line number Diff line number Diff line 
from django.db import models

from django.db.models.expressions import Value

from django.db.models.functions import Cast

from django.test import TestCase



from .models import Author





class CastTests(TestCase):

    @classmethod

    def setUpTestData(self):

        Author.objects.create(name='Bob', age=1)



    def test_cast_from_value(self):

        numbers = Author.objects.annotate(cast_integer=Cast(Value('0'), models.IntegerField()))

        self.assertEqual(numbers.get().cast_integer, 0)



    def test_cast_from_field(self):

        numbers = Author.objects.annotate(cast_string=Cast('age', models.CharField(max_length=255)),)

        self.assertEqual(numbers.get().cast_string, '1')



    def test_cast_from_python(self):

        numbers = Author.objects.annotate(cast_float=Cast(0, models.FloatField()))

        self.assertEqual(numbers.get().cast_float, 0.0)