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django/docs/model-api.txt
Jacob Kaplan-Moss 604cd7fe14 Yes yes yes -- more documentation improvements 
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===============
Model reference
===============
Django's models are the bread and butter of the framework. There's a huge
array of options available to you when defining your data models; this
document explains all of them.
Options for models
==================
A list of all possible options for a model object follows. Although there's a
wide array of possible options, only ``fields`` is required.
``admin``
A ``meta.Admin`` object; see `Admin options`_. If this field isn't given,
the object will not have an admin interface.
``db_table``
The name of the database table to use for the module::
db_table = "pizza_orders"
If not given, this will use ``app_label + '_' + module_name``.
``exceptions``
Names of extra exception subclasses to include in the generated module.
These exceptions are available from instance methods and from module-level
methods::
exceptions = ("DisgustingToppingsException", "BurntCrust")
``fields``
A list of field objects; see `Field objects`_. For example::
fields = (
meta.CharField('customer_name', 'customer name', maxlength=15),
meta.BooleanField('use_extra_cheese', 'use extra cheese'),
meta.IntegerField('customer_type', 'customer type', choices=CUSTOMER_TYPE_CHOICES),
...
)
``get_latest_by``
The name of a date or datetime field; if given, the module will have a
``get_latest()`` function which fetches the "latest" object in terms of
that field::
get_latest_by = "order_date"
``module_constants``
A dict of name/values to use as extra module-level constants::
module_constants = {
'MEAT_TYPE_PEPPERONI' : 1,
'MEAT_TYPE_SAUSAGE' : 2,
}
``module_name``
The name of the module::
module_name = "pizza_orders"
If not given this will use a lowercased version of the class name.
``order_with_respect_to``
Marks this object as "orderable" with respect to the given field. This is
almost always used with related objects to allow them to be ordered with
respect to a parent object. For example, if a ``PizzaToppping`` relates to
a ``Pizza`` object, you might use::
order_with_respect_to = 'pizza_id'
to allow the toppings to be ordered with respect to the associated pizza.
``ordering``
The default ordering for tho object::
ordering = (('order_date', 'DESC'),)
This is a tuple of 2-tuples; each 2-tuple is ``(field_name, ordering_type)``
where ordering_type is either ``"ASC"`` or ``"DESC"``. You may also use the
magic ``(None, "RANDOM")`` ordering tuple for random ordering.
``permissions``
Extra permissions to enter into the permissions table when creating this
object. A add, delete, and change permission is automatically created for
each object; this option specifies extra permissions::
permissions = (("may_delivier_pizzas", "Can deliver pizzas"),)
This is a list of 2-tuples of
``(permission_code, human_readable_permission_name)``.
``unique_together``
Sets of field names that, taken together, must be unique::
unique_together = (("driver_id", "restaurant_id"),)
This is a list of lists of fields that must be unique when considered
together.
``verbose_name``
A human-readable name for the object, singular::
verbose_name = "pizza"
If not given, this will use a munged version of the class name:
``CamelCase`` becomes ``camel case``.
``verbose_name_plural``
The plural name for the object::
verbose_name_plural = "stories"
If not given, ``verbose_name + "s"`` will automatically be used.
Field objects
=============
The list of fields is the most important part of a data model. Each item in
the ``fields`` list is an instance of a ``meta.Field`` subclass, and maps to
a database field.
All field objects -- except for ``ForeignKey`` and ``ManyToManyField`` (see
below) -- take two positional arguments and a number of keyword arguments.
The positional arguments are the field name and the human-readable name. The
field name must be a valid Python identifier, but the human-readable name can
contain spaces, punctuation, etc.
General field options
---------------------
Each type of field takes a different set of options, but there are some
options that are common to all field types. These options are:
====================== ===================================================
Option Description
====================== ===================================================
``blank`` If ``True``, the field is allowed to be blank.
Note that this is different from ``null`` in that
string fields will store the empty string instead of
``NULL`` internally; this means that to create a
field that stores nulls you must pass ``blank=True``
and ``null=True`` .
``choices`` A list of 2-tuples to use as choices for this
field.If this is given, instead of the standard
field a option menu will be used, limiting choices
to the choices given. A choices list looks like::
YEAR_IN_SCHOOL_CHOICES = (
('FR', 'Freshman'),
('SO', 'Sophomore'),
('JR', 'Junior'),
('SR', 'Senior'),
('GR', 'Graduate'),
)
The first element in each tuple is the actual value
to be stored; the second element is the human
readable name for the option.
``core`` For objects that are edited inline to a related
object. If all "core" fields in an inline-edited
object are cleared, the object will be considered to
be deleted.
It is an error to have an inline-editable
relation without at least one core field.
``db_index`` If ``True``, the SQL generator will create a database
index on this field.
``default`` The default value for the field.
``editable`` ``True`` by default, if set to ``False`` the field
will not be editable in the admin.
``help_text`` Extra "help" text to be displayed with the field.
``null`` If ``True`` empty values in the field will be
stored as ``NULL`` in the database.
``primary_key`` If ``True`` this field is the primary key for the
table. You only need to use this if you don't want
the standard "id" field created and used as the
primary key.
Implies ``blank=False``, ``null=False``, and
``unique=True``. Only one primary key is allowed
on each object.
``radio_admin`` If ``choices`` is given, or if the field is a
ManyToOne relation, use a radio button interface
for the choices instead of the standard options
menu interface.
``unique`` If ``True`` this field must be unique throughout
the table.
``unique_for_date`` Set this to the name of a ``DateField`` or
``DateTimeField`` to require that this field
be unique for the value of the date field. That
is, if you have a field, ``title`` that has
``unique_for_date="pub_date"``, then it is an
error to have two rows with the same ``title``
and the same ``pub_date``.
``unique_for_month`` Like ``unique_for_date``, but requires the field
to be unique with respect to the month.
``unique_for_year`` Like ``unique_for_date`` and ``unique_for_month``
but, well, you get the idea.
``validator_list`` A list of extra validators to apply to the field.
See the `Form fields guide`_ for information about
validators.
====================== ===================================================
.. _`Form fields guide`: http://www.djangoproject.com/FIXME/
Field Types
-----------
``AutoField``
An ``IntegerField`` that automatically increments. You usually won't need to
use this directly; a primary key field will automatically be added to your
model if you don't specify otherwise. That automatically added field is::
meta.AutoField('id', 'ID', primary_key=True)
``BooleanField``
A true/false field.
``CharField``
A text field. These are displayed in the admin as single-line text inputs, so
for large amounts of text use a ``TextField``.
``CharField``s have an extra required argument: ``maxlength``; the maximum
length (in characters) of the field.
``CommaSeparatedIntegerField``
A field of integers separated by commas.
``DateField``
A, um, date field. Has a few extra optional options:
====================== ===================================================
Option Description
====================== ===================================================
``auto_now`` Automatically set the field to now every time the
object is saved. Useful for "last-modified"
timestamps.
``auto_now_add`` Automatically set the field to now when the object
is first created. Useful for creation timestamps.
====================== ===================================================
``DateTimeField``
A date and time field. Takes the same extra options as ``DateField``.
``EmailField``
A ``CharField`` that checks that the value is a valid email address. Because
validating email addresses can be tricky, this is a pretty loose test.
``FileField``
A file-upload field. Takes on additional option, ``upload_to`` which is
a path to upload the file to. This path may contain `strftime formatting`_
which will be replaced by the date/time of the file upload (so that uploaded
files don't fill up the given directory).
.. _`strftime formatting`: http://docs.python.org/lib/module-time.html#l2h-1941
``FloatField``
A floating-point number. Has two additional required options:
====================== ===================================================
Option Description
====================== ===================================================
``max_digits`` The maximum number of digits allowed in the number.
``decimal_places`` The number of decimal places to store with the
number
====================== ===================================================
For example, to store numbers up to 999 with a resolution of 2 decimal places,
you'd use::
meta.FloatField(..., max_digits=5, decimal_places=2)
And to store numbers up to one million with a resolution of 10 decimal places::
meta.FloatField(..., max_digits=19, decimal_places=10)
``ForeignKey``
A many-to-one relationship to the primary key in another object. So, to give a
``Topping`` object a many-to-one relationship to ``Pizza`` (i.e. there are
many toppings on a pizza)::
meta.ForeignKey(Pizza)
``ForeignKey`` fields take a large number of extra options for defining how
the relationship should work:
======================= ============================================================
Option Description
======================= ============================================================
``edit_inline`` If ``True``, this related object is edited
"inline" on the related object's page. This means
that the object will not have its own admin
interface.
``edit_inline_type`` This is either ``meta.TABULAR`` or
``meta.STACKED`` and controls weather the inline
editable objects are displayed as a table or as
a "stack" of fieldsets. Defaults to
``meta.STACKED``.
``limit_choices_to`` A dictionary of lookup arguments and values (see
the `Database API reference`_) to limit choices
of this object to. Use this along with
``meta.LazyDate`` to limit choices of objects
by date, for example::
limit_choices_to = {'pub_date__lte' : meta.LazyDate()}
only allows the choice of related objects with a
``pub_date`` before the current date/time to be
chosen.
Not compatible with ``edit_inline``.
``max_num_in_admin`` For inline-edited objects, this is the maximum
number of related objects to display in the admin.
Thus, if a pizza could only have up to 10
toppings, ``max_num_in_admin=10`` would ensure
that a user never enters more than 10 toppings.
Note that this doesn't ensure more than 10 related
toppings ever get created.
``min_num_in_admin`` The minimum number of related objects displayed in
the admin. Normally, at the creation stage
``num_in_admin`` inline objects are shown, and at
the edit stage ``num_extra_on_change`` objects are
shown in addition to all pre-existing related
objects. However, no fewer than
``min_num_in_admin`` related objects will ever be
displayed.
``num_extra_on_change`` The number of extra blank related object fields to
show at the change stage.
``num_in_admin`` The default number of inline objects to display
on the object page at the add stage.
``raw_id_admin`` Only display a field for the integer to be entered
instead of a drop-down menu. This is useful when
related to an object type that will have too many
rows to make a menu practical.
Not used with ``edit_inline``.
``rel_name`` The name of the relation. In the above example,
this would default to 'pizza' (so that the
``Toppings`` object would have a ``get_pizza()``
function; if you set ``rel_name`` to "pie", then
the function would be called ``get_pie()`` and the
field name would be ``pie_id``.
``related_name`` The name to use for the relation from the related
object back to this one. For example, when if
``Topping`` has this field::
meta.ForeignKey(Pizza)
the ``related_name`` will be "topping" (taken from
the class name which will in turn give ``Pizza``
methods like ``get_topping_list()`` and
``get_topping_count()``.
If you instead were to use::
meta.ForeignKey(Pizza, related_name="munchie")
then the methods would be called
``get_munchie_list()``, ``get_munchie_count()``,
etc.
This is only really useful when you have a single
object that relates to the same object more than
once. For example, if a ``Story`` object has both
``primary_category`` and ``secondary_category``
fields, to make sure that the category objects
have the correct methods, you'd use fields like::
...
meta.ForeignKey(Category, name="primary_category_id",
rel_name="primary_category",
related_name="primary_story"),
meta.ForeignKey(Category, name="secondary_category_id",
rel_name="secondary_category",
related_name="secondary_story"),
...
which would give the category objects methods
named ``get_primary_story_list()`` and
``get_secondary_story_list()``.
``to_field`` The field on the related object that the relation
is to. This is almost always ``id``, but if the
PK on the other object is named something
different, this is how to indicate that.
======================= ============================================================
.. _`Database API reference`: http://www.djangoproject.com/documentation/db_api/
``ImageField``
Like a ``FieldField``, but validates that the uploaded object is a valid
image. Has two extra optional arguments, ``height_field`` and ``width_field``
which, if set, will be auto-populated with the height and width of the image.
``IntegerField``
An integer, surprisingly.
``IPAddressField``
An IP address, in string format (i.e. "24.124.1.30").
``ManyToManyField``
A many-to-many relation to another object. For example (taken from the
``core.flatfiles`` object::
class FlatFile(meta.Model):
fields = (
...
meta.ManyToManyField(Site),
)
Many-to-many relations are a bit different from other fields. First, they
aren't actually a field per se since they use a intermediary join table.
Second, they don't take any of the same options as the rest of the fields,
the only options taken are:
======================= ============================================================
Option Description
======================= ============================================================
``related_name`` See the description of ``related_name`` in
``ManyToOneField``, above.
``filter_interface`` Use a nifty unobtrusive Javascript "filter" interface
instead of the usability-challenged ``<select multiple>``.
The value should be ``meta.HORIZONTAL`` or ``meta.VERTICAL``
(i.e. should the interface be stacked horizontally or
vertically).
``limit_choices_to`` See the description under ``ManyToOneField``, above.
======================= ============================================================
``NullBooleanField``
Like a ``BooleanField``, but allows ``NULL`` as one of the options. Use this
instead of a ``BooleanField`` with ``null=True`` .
``OneToOneField``
Signifies a one-to-one relationship. This is most useful on the primary key
of an object when that object "extends" another object in some way.
For example, if you are building a database of "places", you would build pretty
standard stuff like address, phone number, etc. in the database. If you then
wanted to build a database of restaurants on top of the places, instead of
repeating yourself and replicating those fields in the restaurants object, you
could make ``Restaurant`` have a ``OneToOneField`` to ``Place`` (since
a restaurant "is-a" place). This ``OneToOneField`` will actually replace
the primary key ``id`` field (since one-to-one relations share the same
primary key), and has a few in the admin interface:
* No selection interface is displayed on ``Restaurant`` pages; there will
be one (and only one) ``Restaurant`` for each place.
* On the ``Restaurant`` change list, every single ``Place`` -- weather it
has an associated ``Restaurant`` or not -- will be displayed. Adding
a ``Restaurant`` to a ``Place`` just means filling out the required
``Restaurant`` fields.
``PhoneNumberField``
Validates that the value is a valid phone number.
``PositiveIntegerField``
Like an ``IntegerField``, but must be positive.
``PositiveSmallIntegerField``
Like a ``PositiveIntegerField``, but only allows values below 32767.
``SlugField``
A "slug" suitable for parts of a URL; only allows alpha-numeric characters and
underscores.
Implies ``maxlength=50`` and ``db_index=True``.
Accepts an extra option, ``prepopulate_from`` which is a list of fields from
which to auto-populate the slug.
``SmallIntegerField``
Like an ``IntegerField``, but must be between -32768 and 32767.
``TextField``
A large text field (``<textarea>`` in HTML).
``TimeField``
A time. Accepts the same auto-population options as ``DateField`` and
``DateTimeField``.
``URLField``
A field for a URL. If the ``verify_exists`` option is ``True``, the URL given
will be checked for existence (i.e. actually loads and doesn't give a 404
response).
``USStateField``
A US state.
``XMLField``
A field containing XML. Takes one required argument, ``schema_path`` which
is the path to a RelaxNG_ scheme against which to validate the field.
.. _RelaxNG: http://www.relaxng.org/
Admin options
=============
The ``admin`` field in the model tells Django how to construct the admin
interface for the object. The field is an instance of the ``meta.Admin``
object, which has the following options (of which only ``fields`` is required):
``date_hierarchy``
To allow filtering of objects in the admin by date, set ``date_hierarchy``
to the name of the field to filter by::
date_hierarchy = 'order_date'
``fields``
A list of fieldsets to display on the admin page. Each fieldset is a 2-tuple:
``(name, field_options)``. The ``name`` is a string to name the field set,
and ``field_options`` is a dictionary of information about the fields to be
displayed in that fieldset. This dictionary has the following keys:
``fields``
A tuple of field names to display in this fieldset. To display
multiple fields on the same line, wrap those fields in their
own tuple.
This key is required in the dict.
``classes``
Extra CSS classes to apply to the fieldset. This is a simple
string; you can apply multiple classes by separating them with
spaces.
Two useful classes defined by the default stylesheet are ``collapse``
and ``wide``. Fieldsets with the ``collapse`` style will be
initially collapsed in the admin and replaced with a small "click
to expand" link. Fieldsets with the ``wide`` style will be given
extra horizontal space.
For example (taken from the ``core.flatfiles`` model)::
fields = (
(None, {
'fields': ('url', 'title', 'content', 'sites')
}),
('Advanced options', {
'classes': 'collapse',
'fields' : ('enable_comments', 'registration_required', 'template_name')
}),
),
results in an admin that looks like:
.. image:: http://media.djangoproject.com/img/doc/flatfiles_admin.png
``js``
Extra JavaScript files to link into the admin screen. This can be used to
tweak a given type of admin page in JS or to provide "quick links" to fill
in default values for certain fields.
``list_display``
List of fields to display on the list page in the admin.
There are a few special cases that do other things besides displaying the
contents of the given fields:
* If the field given has a relationship, that relationship is
followed and the ``repr()`` of the related object is displayed.
* If the field is a ``BooleanField``, a "on" or "off" icon will
be displayed instead of ``True`` or ``False``.
* If the field name given does not exist, a function of the model
will be searched for and called if present. This function
should have a ``short_description`` attribute that will be
used as the header for the field.
See the exmaple below.
``list_filter``
List of fields to filter by. Each field should either be a ``BooleanField``
or else a field with a ``ManyToOne`` relation.
An example of how ``list_display`` and ``list_filter`` work (taken from
the ``auth.user`` model)::
list_display = ('username', 'email', 'first_name', 'last_name', 'is_staff'),
list_filter = ('is_staff', 'is_superuser'),
results in a admin that looks like:
.. image:: http://media.djangoproject.com/img/doc/users_changelist.png
(This example also has ``search_fields`` defined; see below).
``ordering``
An ordering tuple (see the `Options for models`_, above) that gives a
different ordering for the admin change list. If not given, the model's
default ordering will be used.
``save_as``
Enables a "save as" feature on object pages. Normally, objects have three
save options: "Save", "Save and continue editing", and "Save and add
another". If ``save_as`` is ``True``, "Save and add another" will be
replaced by a "Save as" button.
``save_on_top``
If this option is ``True``, object pages will have the save buttons across
the top as well as at the bottom of the page.
``search_fields``
A list of fields to provide a text search for. These fields should,
obviously, be some kind of text field.
Model methods
=============
There are a number of methods you can define on model objects to control the
object's behavior. First, any methods you define will be available as methods
of object instances. For example::
class Pizza(meta.Model):
fields = (
...
)
def is_disgusting(self):
return "anchovices" in [topping.name for topping in self.get_topping_list()]
Now, every ``Pizza`` object will have a ``is_disgusting()`` method.
There are a few object methods that have special meaning:
``__repr__``
Django uses ``repr(obj)`` in a number of places, the most notable as the
value inserted into a template when it displays an object. Thus, you should
return a nice, human-readable string for the object's ``__repr__``.
``get_absolute_url``
If an object defines a ``get_absolute_url`` method, it is used to
associate a URL with an object. For example:
def get_absolute_url(self):
return "/pizzas/%i/" % self.id
The most useful place this is used is in the admin interface; if an object
defines ``get_absolute_url`` then the object detail page will have a "View
on site" link that will jump you directly to the object's public view.
``_pre_save``
This method will be called just before the object is saved into the
database; you can use it to (for example) calculate aggregate values from
other fields before the object is saved.
``_post_save``
Called just after the object is saved to the database. This could be used
to update other tables, update cached information, etc.
Module-level methods
--------------------
Since each data class in effect turns into a module, there are times you'll want
to write methods that live in that module. Any model method that begins with
"_module_" is turned into a module-level method::
class Pizza(meta.Model):
fields = (
...
)
def _module_get_pizzas_to_deliver():
return get_list(delivered__exact=False)
This will make the top-level ``pizzas`` module have a ``get_pizzas_to_deliver()``
method::
>>> from django.models.pizza_hut import pizzas
>>> pizzas.get_pizzas_to_deliver()
[ ... ]
Note that the scope of these methods is modified to be the same has the module
scope (so that's how the raw ``get_list`` works).
Manipulator methods
-------------------
Similarly, you can add methods to the object's manipulators (see the formfields
documentation for more on manipulators) by defining methods that being with
"_manipulator_". This is most useful for providing custom validators for certain
fields since manipulators automatically call any method that begins with
"validate"::
class Pizza(meta.Model):
fields = (
...
)
def _manipulator_validate_customer_id(self, field_data, all_data):
from django.core import validators
from django.conf.settings import BAD_CUSTOMER_IDS
if int(field_data) in BAD_CUSTOMER_IDS:
raise validators.ValidationError("We don't deliver to this customer")
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