A model is the single, definitive source of data about your data. It contains the essential fields and behaviors of the data you’re storing. Generally, each model maps to a single database table.
The basics:
A companion to this document is the official repository of model examples. (In the Django source distribution, these examples are in the tests/modeltests directory.)
This example model defines a Person, which has a first_name and last_name:
from django.db import models
class Person(models.Model):
first_name = models.CharField(maxlength=30)
last_name = models.CharField(maxlength=30)
first_name and last_name are fields of the model. Each field is specified as a class attribute, and each attribute maps to a database column.
The above Person model would create a database table like this:
CREATE TABLE myapp_person (
"id" serial NOT NULL PRIMARY KEY,
"first_name" varchar(30) NOT NULL,
"last_name" varchar(30) NOT NULL
);
Some technical notes:
The most important part of a model — and the only required part of a model — is the list of database fields it defines. Fields are specified by class attributes.
Example:
class Musician(models.Model):
first_name = models.CharField(maxlength=50)
last_name = models.CharField(maxlength=50)
instrument = models.CharField(maxlength=100)
class Album(models.Model):
artist = models.ForeignKey(Musician)
name = models.CharField(maxlength=100)
release_date = models.DateField()
num_stars = models.IntegerField()
Django places only two restrictions on model field names:
A field name cannot be a Python reserved word, because that would result in a Python syntax error. For example:
class Example(models.Model):
pass = models.IntegerField() # 'pass' is a reserved word!
A field name cannot contain more than one underscore in a row, due to the way Django’s query lookup syntax works. For example:
class Example(models.Model):
foo__bar = models.IntegerField() 'foo__bar' has two underscores!
These limitations can be worked around, though, because your field name doesn’t necessarily have to match your database column name. See db_column below.
SQL reserved words, such as join, where or select, are allowed as model field names, because Django escapes all database table names and column names in every underlying SQL query. It uses the quoting syntax of your particular database engine.
Each field in your model should be an instance of the appropriate Field class. Django uses the field class types to determine a few things:
Here are all available field types:
An IntegerField that automatically increments according to available IDs. 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. See Automatic primary key fields.
A true/false field.
The admin represents this as a checkbox.
A string field, for small- to large-sized strings.
For large amounts of text, use TextField.
The admin represents this as an <input type="text"> (a single-line input).
CharField has an extra required argument, maxlength, the maximum length (in characters) of the field. The maxlength is enforced at the database level and in Django’s validation.
A field of integers separated by commas. As in CharField, the maxlength argument is required.
A date field. Has a few extra optional arguments:
| Argument | Description |
|---|---|
| auto_now | Automatically set the field to now every time the object is saved. Useful for “last-modified” timestamps. Note that the current date is always used; it’s not just a default value that you can override. |
| auto_now_add | Automatically set the field to now when the object is first created. Useful for creation of timestamps. Note that the current date is always used; it’s not just a default value that you can override. |
The admin represents this as an <input type="text"> with a JavaScript calendar and a shortcut for “Today.”
A date and time field. Takes the same extra options as DateField.
The admin represents this as two <input type="text"> fields, with JavaScript shortcuts.
A CharField that checks that the value is a valid e-mail address. This doesn’t accept maxlength.
A file-upload field.
Has an extra required argument, upload_to, a local filesystem path to which files should be upload. 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).
The admin represents this as an <input type="file"> (a file-upload widget).
Using a FileField or an ImageField (see below) in a model takes a few steps:
A field whose choices are limited to the filenames in a certain directory on the filesystem. Has three special arguments, of which the first is required:
| Argument | Description |
|---|---|
| path | Required. The absolute filesystem path to a directory from which this FilePathField should get its choices. Example: "/home/images". |
| match | Optional. A regular expression, as a string, that FilePathField will use to filter filenames. Note that the regex will be applied to the base filename, not the full path. Example: "foo.*\.txt^", which will match a file called foo23.txt but not bar.txt or foo23.gif. |
| recursive | Optional. Either True or False. Default is False. Specifies whether all subdirectories of path should be included. |
Of course, these arguments can be used together.
The one potential gotcha is that match applies to the base filename, not the full path. So, this example:
FilePathField(path="/home/images", match="foo.*", recursive=True)
…will match /home/images/foo.gif but not /home/images/foo/bar.gif because the match applies to the base filename (foo.gif and bar.gif).
A floating-point number. Has two required arguments:
| Argument | 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:
models.FloatField(..., max_digits=5, decimal_places=2)
And to store numbers up to approximately one billion with a resolution of 10 decimal places:
models.FloatField(..., max_digits=19, decimal_places=10)
The admin represents this as an <input type="text"> (a single-line input).
Like FileField, 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 each time a model instance is saved.
Requires the Python Imaging Library.
An integer.
The admin represents this as an <input type="text"> (a single-line input).
An IP address, in string format (i.e. “24.124.1.30”).
The admin represents this as an <input type="text"> (a single-line input).
Like a BooleanField, but allows NULL as one of the options. Use this instead of a BooleanField with null=True.
The admin represents this as a <select> box with “Unknown”, “Yes” and “No” choices.
A CharField that checks that the value is a valid U.S.A.-style phone number (in the format XXX-XXX-XXXX).
Like an IntegerField, but must be positive.
Like a PositiveIntegerField, but only allows values under a certain (database-dependent) point.
“Slug” is a newspaper term. A slug is a short label for something, containing only letters, numbers, underscores or hyphens. They’re generally used in URLs.
In the Django development version, you can specify maxlength. If maxlength is not specified, Django will use a default length of 50. In previous Django versions, there’s no way to override the length of 50.
Implies db_index=True.
Accepts an extra option, prepopulate_from, which is a list of fields from which to auto-populate the slug, via JavaScript, in the object’s admin form:
models.SlugField(prepopulate_from=("pre_name", "name"))
prepopulate_from doesn’t accept DateTimeFields.
The admin represents SlugField as an <input type="text"> (a single-line input).
Like an IntegerField, but only allows values under a certain (database-dependent) point.
A large text field.
The admin represents this as a <textarea> (a multi-line input).
A time. Accepts the same auto-population options as DateField and DateTimeField.
The admin represents this as an <input type="text"> with some JavaScript shortcuts.
A field for a URL. If the verify_exists option is True (default), the URL given will be checked for existence (i.e., the URL actually loads and doesn’t give a 404 response).
The admin represents this as an <input type="text"> (a single-line input).
A two-letter U.S. state abbreviation.
The admin represents this as an <input type="text"> (a single-line input).
A TextField that checks that the value is valid XML that matches a given schema. Takes one required argument, schema_path, which is the filesystem path to a RelaxNG schema against which to validate the field.
The following arguments are available to all field types. All are optional.
If True, Django will store empty values as NULL in the database. Default is False.
Note that empty string values will always get stored as empty strings, not as NULL — so use null=True for non-string fields such as integers, booleans and dates.
Avoid using null on string-based fields such as CharField and TextField unless you have an excellent reason. If a string-based field has null=True, that means it has two possible values for “no data”: NULL, and the empty string. In most cases, it’s redundant to have two possible values for “no data;” Django convention is to use the empty string, not NULL.
If True, the field is allowed to be blank.
Note that this is different than null. null is purely database-related, whereas blank is validation-related. If a field has blank=True, validation on Django’s admin site will allow entry of an empty value. If a field has blank=False, the field will be required.
An iterable (e.g., a list or tuple) of 2-tuples to use as choices for this field.
If this is given, Django’s admin will use a select box instead of the standard text field and will limit choices to the choices given.
A choices list looks like this:
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.
The choices list can be defined either as part of your model class:
class Foo(models.Model):
GENDER_CHOICES = (
('M', 'Male'),
('F', 'Female'),
)
gender = models.CharField(maxlength=1, choices=GENDER_CHOICES)
or outside your model class altogether:
GENDER_CHOICES = (
('M', 'Male'),
('F', 'Female'),
)
class Foo(models.Model):
gender = models.CharField(maxlength=1, choices=GENDER_CHOICES)
Finally, note that choices can be any iterable object — not necessarily a list or tuple. This lets you construct choices dynamically. But if you find yourself hacking choices to be dynamic, you’re probably better off using a proper database table with a ForeignKey. choices is meant for static data that doesn’t change much, if ever.
For objects that are edited inline to a related object.
In the Django admin, if all “core” fields in an inline-edited object are cleared, the object will be deleted.
It is an error to have an inline-editable relation without at least one core=True field.
Please note that each field marked “core” is treated as a required field by the Django admin site. Essentially, this means you should put core=True on all required fields in your related object that is being edited inline.
The name of the database column to use for this field. If this isn’t given, Django will use the field’s name.
If your database column name is an SQL reserved word, or contains characters that aren’t allowed in Python variable names — notably, the hyphen — that’s OK. Django quotes column and table names behind the scenes.
If True, django-admin.py sqlindexes will output a CREATE INDEX statement for this field.
The default value for the field.
If False, the field will not be editable in the admin. Default is True.
Extra “help” text to be displayed under the field on the object’s admin form. It’s useful for documentation even if your object doesn’t have an admin form.
If True, this field is the primary key for the model.
If you don’t specify primary_key=True for any fields in your model, Django will automatically add this field:
id = models.AutoField('ID', primary_key=True)
Thus, you don’t need to set primary_key=True on any of your fields unless you want to override the default primary-key behavior.
primary_key=True implies blank=False, null=False and unique=True. Only one primary key is allowed on an object.
By default, Django’s admin uses a select-box interface (<select>) for fields that are ForeignKey or have choices set. If radio_admin is set to True, Django will use a radio-button interface instead.
Don’t use this for a field unless it’s a ForeignKey or has choices set.
If True, this field must be unique throughout the table.
This is enforced at the database level and at the Django admin-form level.
Set this to the name of a DateField or DateTimeField to require that this field be unique for the value of the date field.
For example, if you have a field title that has unique_for_date="pub_date", then Django wouldn’t allow the entry of two records with the same title and pub_date.
This is enforced at the Django admin-form level but not at the database level.
Like unique_for_date, but requires the field to be unique with respect to the month.
Like unique_for_date and unique_for_month.
A list of extra validators to apply to the field. Each should be a callable that takes the parameters field_data, all_data and raises django.core.validators.ValidationError for errors. (See the validator docs.)
Django comes with quite a few validators. They’re in django.core.validators.
Each field type, except for ForeignKey, ManyToManyField and OneToOneField, takes an optional first positional argument — a verbose name. If the verbose name isn’t given, Django will automatically create it using the field’s attribute name, converting underscores to spaces.
In this example, the verbose name is "Person's first name":
first_name = models.CharField("Person's first name", maxlength=30)
In this example, the verbose name is "first name":
first_name = models.CharField(maxlength=30)
ForeignKey, ManyToManyField and OneToOneField require the first argument to be a model class, so use the verbose_name keyword argument:
poll = models.ForeignKey(Poll, verbose_name="the related poll") sites = models.ManyToManyField(Site, verbose_name="list of sites") place = models.OneToOneField(Place, verbose_name="related place")
Convention is not to capitalize the first letter of the verbose_name. Django will automatically capitalize the first letter where it needs to.
Clearly, the power of relational databases lies in relating tables to each other. Django offers ways to define the three most common types of database relationships: Many-to-one, many-to-many and one-to-one.
To define a many-to-one relationship, use ForeignKey. You use it just like any other Field type: by including it as a class attribute of your model.
ForeignKey requires a positional argument: The class to which the model is related.
For example, if a Car model has a Manufacturer — that is, a Manufacturer makes multiple cars but each Car only has one Manufacturer — use the following definitions:
class Manufacturer(models.Model):
# ...
class Car(models.Model):
manufacturer = models.ForeignKey(Manufacturer)
# ...
To create a recursive relationship — an object that has a many-to-one relationship with itself — use models.ForeignKey('self').
If you need to create a relationship on a model that has not yet been defined, you can use the name of the model, rather than the model object itself:
class Car(models.Model):
manufacturer = models.ForeignKey('Manufacturer')
# ...
class Manufacturer(models.Model):
# ...
Note, however, that support for strings around model names in ForeignKey is quite new, and it can be buggy in some cases.
Behind the scenes, Django appends "_id" to the field name to create its database column name. In the above example, the database table for the Car model will have a manufacturer_id column. (You can change this explicitly by specifying db_column; see db_column below.) However, your code should never have to deal with the database column name, unless you write custom SQL. You’ll always deal with the field names of your model object.
It’s suggested, but not required, that the name of a ForeignKey field (manufacturer in the example above) be the name of the model, lowercase. You can, of course, call the field whatever you want. For example:
class Car(models.Model):
company_that_makes_it = models.ForeignKey(Manufacturer)
# ...
See the Many-to-one relationship model example for a full example.
ForeignKey fields take a number of extra arguments for defining how the relationship should work. All are optional:
| Argument | Description |
|---|---|
| edit_inline | If not False, this related object is edited “inline” on the related object’s page. This means that the object will not have its own admin interface. Use either models.TABULAR or models.STACKED, which, respectively, designate whether the inline-editable objects are displayed as a table or as a “stack” of fieldsets. |
| limit_choices_to | A dictionary of lookup arguments and values (see the Database API reference) that limit the available admin choices for this object. Use this with models.LazyDate to limit choices of objects by date. For example:
limit_choices_to = {'pub_date__lte': models.LazyDate()}
only allows the choice of related objects with a pub_date before the current date/time to be chosen. Instead of a dictionary this can also be a Q object (an object with a get_sql() method) for more complex queries. 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. It simply controls the admin interface; it doesn’t enforce things at the Python API level or database level. |
| 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 blank 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 select box practical. Not used with edit_inline. |
| related_name | The name to use for the relation from the related object back to this one. See the related objects documentation for a full explanation and example. |
| to_field | The field on the related object that the relation is to. By default, Django uses the primary key of the related object. |
To define a many-to-many relationship, use ManyToManyField. You use it just like any other Field type: by including it as a class attribute of your model.
ManyToManyField requires a positional argument: The class to which the model is related.
For example, if a Pizza has multiple Topping objects — that is, a Topping can be on multiple pizzas and each Pizza has multiple toppings — here’s how you’d represent that:
class Topping(models.Model):
# ...
class Pizza(models.Model):
# ...
toppings = models.ManyToManyField(Topping)
As with ForeignKey, a relationship to self can be defined by using the string 'self' instead of the model name, and you can refer to as-yet undefined models by using a string containing the model name.
It’s suggested, but not required, that the name of a ManyToManyField (toppings in the example above) be a plural describing the set of related model objects.
Behind the scenes, Django creates an intermediary join table to represent the many-to-many relationship.
It doesn’t matter which model gets the ManyToManyField, but you only need it in one of the models — not in both.
Generally, ManyToManyField instances should go in the object that’s going to be edited in the admin interface, if you’re using Django’s admin. In the above example, toppings is in Pizza (rather than Topping having a pizzas ManyToManyField ) because it’s more natural to think about a Pizza having toppings than a topping being on multiple pizzas. The way it’s set up above, the Pizza admin form would let users select the toppings.
See the Many-to-many relationship model example for a full example.
ManyToManyField objects take a number of extra arguments for defining how the relationship should work. All are optional:
| Argument | Description |
|---|---|
| related_name | See the description under ForeignKey above. |
| filter_interface | Use a nifty unobtrusive Javascript “filter” interface instead of the usability-challenged <select multiple> in the admin form for this object. The value should be models.HORIZONTAL or models.VERTICAL (i.e. should the interface be stacked horizontally or vertically). |
| limit_choices_to | See the description under ForeignKey above. |
| symmetrical | Only used in the definition of ManyToManyFields on self. Consider the following model:
When Django processes this model, it identifies that it has a ManyToManyField on itself, and as a result, it doesn’t add a person_set attribute to the Person class. Instead, the ManyToManyField is assumed to be symmetrical — that is, if I am your friend, then you are my friend. If you do not want symmetry in ManyToMany relationships with self, set symmetrical to False. This will force Django to add the descriptor for the reverse relationship, allowing ManyToMany relationships to be non-symmetrical. |
The semantics of one-to-one relationships will be changing soon, so we don’t recommend you use them. If that doesn’t scare you away, keep reading.
To define a one-to-one relationship, use OneToOneField. You use it just like any other Field type: by including it as a class attribute of your model.
This is most useful on the primary key of an object when that object “extends” another object in some way.
OneToOneField requires a positional argument: The class to which the model is related.
For example, if you’re building a database of “places”, you would build pretty standard stuff such as address, phone number, etc. in the database. Then, if you wanted to build a database of restaurants on top of the places, instead of repeating yourself and replicating those fields in the Restaurant model, you could make Restaurant have a OneToOneField to Place (because a restaurant “is-a” place).
As with ForeignKey, a relationship to self can be defined by using the string "self" instead of the model name; references to as-yet undefined models can be made by using a string containing the model name.
This OneToOneField will actually replace the primary key id field (since one-to-one relations share the same primary key), and will be displayed as a read-only field when you edit an object in the admin interface:
See the One-to-one relationship model example for a full example.
Give your model metadata by using an inner class Meta, like so:
class Foo(models.Model):
bar = models.CharField(maxlength=30)
class Meta:
# ...
Model metadata is “anything that’s not a field”, such as ordering options, etc.
Here’s a list of all possible Meta options. No options are required. Adding class Meta to a model is completely optional.
The name of the database table to use for the model:
db_table = 'music_album'
If this isn’t given, Django will use app_label + '_' + model_class_name. See “Table names” below for more.
If your database table name is an SQL reserved word, or contains characters that aren’t allowed in Python variable names — notably, the hyphen — that’s OK. Django quotes column and table names behind the scenes.
The name of a DateField or DateTimeField in the model. This specifies the default field to use in your model Manager‘s latest() method.
Example:
get_latest_by = "order_date"
See the docs for latest() for more.
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 an Answer relates to a Question object, and a question has more than one answer, and the order of answers matters, you’d do this:
class Answer(models.Model):
question = models.ForeignKey(Question)
# ...
class Meta:
order_with_respect_to = 'question'
The default ordering for the object, for use when obtaining lists of objects:
ordering = ['-order_date']
This is a tuple or list of strings. Each string is a field name with an optional “-” prefix, which indicates descending order. Fields without a leading “-” will be ordered ascending. Use the string “?” to order randomly.
For example, to order by a pub_date field ascending, use this:
ordering = ['pub_date']
To order by pub_date descending, use this:
ordering = ['-pub_date']
To order by pub_date descending, then by author ascending, use this:
ordering = ['-pub_date', 'author']
See Specifying ordering for more examples.
Note that, regardless of how many fields are in ordering, the admin site uses only the first field.
Extra permissions to enter into the permissions table when creating this object. Add, delete and change permissions are automatically created for each object that has admin set. This example specifies an extra permission, can_deliver_pizzas:
permissions = (("can_deliver_pizzas", "Can deliver pizzas"),)
This is a list or tuple of 2-tuples in the format (permission_code, human_readable_permission_name).
Sets of field names that, taken together, must be unique:
unique_together = (("driver", "restaurant"),)
This is a list of lists of fields that must be unique when considered together. It’s used in the Django admin and is enforced at the database level (i.e., the appropriate UNIQUE statements are included in the CREATE TABLE statement).
A human-readable name for the object, singular:
verbose_name = "pizza"
If this isn’t given, Django will use a munged version of the class name: CamelCase becomes camel case.
The plural name for the object:
verbose_name_plural = "stories"
If this isn’t given, Django will use verbose_name + "s".
To save you time, Django automatically derives the name of the database table from the name of your model class and the app that contains it. A model’s database table name is constructed by joining the model’s “app label” — the name you used in manage.py startapp — to the model’s class name, with an underscore between them.
For example, if you have an app bookstore (as created by manage.py startapp bookstore), a model defined as class Book will have a database table named bookstore_book.
To override the database table name, use the db_table parameter in class Meta.
By default, Django gives each model the following field:
id = models.AutoField(primary_key=True)
This is an auto-incrementing primary key.
If you’d like to specify a custom primary key, just specify primary_key=True on one of your fields. If Django sees you’ve explicitly set primary_key, it won’t add the automatic id column.
Each model requires exactly one field to have primary_key=True.
If you want your model to be visible to Django’s admin site, give your model an inner "class Admin", like so:
class Person(models.Model):
first_name = models.CharField(maxlength=30)
last_name = models.CharField(maxlength=30)
class Admin:
# Admin options go here
pass
The Admin class tells Django how to display the model in the admin site.
Here’s a list of all possible Admin options. None of these options are required. To use an admin interface without specifying any options, use pass, like so:
class Admin:
pass
Adding class Admin to a model is completely optional.
Set date_hierarchy to the name of a DateField or DateTimeField in your model, and the change list page will include a date-based drilldown navigation by that field.
Example:
date_hierarchy = 'pub_date'
Set fields to control the layout of admin “add” and “change” pages.
fields is a list of two-tuples, in which each two-tuple represents a <fieldset> on the admin form page. (A <fieldset> is a “section” of the form.)
The two-tuples are in the format (name, field_options), where name is a string representing the title of the fieldset and field_options is a dictionary of information about the fieldset, including a list of fields to be displayed in it.
A full example, taken from the django.contrib.flatpages.FlatPage model:
class Admin:
fields = (
(None, {
'fields': ('url', 'title', 'content', 'sites')
}),
('Advanced options', {
'classes': 'collapse',
'fields' : ('enable_comments', 'registration_required', 'template_name')
}),
)
This results in an admin page that looks like:
If fields isn’t given, Django will default to displaying each field that isn’t an AutoField and has editable=True, in a single fieldset, in the same order as the fields are defined in the model.
The field_options dictionary can have the following keys:
A tuple of field names to display in this fieldset. This key is required.
Example:
{
'fields': ('first_name', 'last_name', 'address', 'city', 'state'),
}
To display multiple fields on the same line, wrap those fields in their own tuple. In this example, the first_name and last_name fields will display on the same line:
{
'fields': (('first_name', 'last_name'), 'address', 'city', 'state'),
}
A string containing extra CSS classes to apply to the fieldset.
Example:
{
'classes': 'wide',
}
Apply multiple classes by separating them with spaces. Example:
{
'classes': 'wide extrapretty',
}
Two useful classes defined by the default admin-site 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.
A string of optional extra text to be displayed at the top of each fieldset, under the heading of the fieldset. It’s used verbatim, so you can use any HTML and you must escape any special HTML characters (such as ampersands) yourself.
A list of strings representing URLs of JavaScript files to link into the admin screen via <script src=""> tags. This can be used to tweak a given type of admin page in JavaScript or to provide “quick links” to fill in default values for certain fields.
Set list_display to control which fields are displayed on the change list page of the admin.
Example:
list_display = ('first_name', 'last_name')
If you don’t set list_display, the admin site will display a single column that displays the __str__() representation of each object.
A few special cases to note about list_display:
If the field is a ForeignKey, Django will display the __str__() of the related object.
executing a separate SQL statement for each row in the table.
If the field is a BooleanField, Django will display a pretty “on” or “off” icon instead of True or False.
If the string given is a method of the model, Django will call it and display the output. This method should have a short_description function attribute, for use as the header for the field.
Here’s a full example model:
class Person(models.Model):
name = models.CharField(maxlength=50)
birthday = models.DateField()
class Admin:
list_display = ('name', 'decade_born_in')
def decade_born_in(self):
return self.birthday.strftime('%Y')[:3] + "0's"
decade_born_in.short_description = 'Birth decade'
If the string given is a method of the model, Django will HTML-escape the output by default. If you’d rather not escape the output of the method, give the method an allow_tags attribute whose value is True.
Here’s a full example model:
class Person(models.Model):
first_name = models.CharField(maxlength=50)
last_name = models.CharField(maxlength=50)
color_code = models.CharField(maxlength=6)
class Admin:
list_display = ('first_name', 'last_name', 'colored_name')
def colored_name(self):
return '<span style="color: #%s;">%s %s</span>' % (self.color_code, self.first_name, self.last_name)
colored_name.allow_tags = True
Set list_display_links to control which fields in list_display should be linked to the “change” page for an object.
By default, the change list page will link the first column — the first field specified in list_display — to the change page for each item. But list_display_links lets you change which columns are linked. Set list_display_links to a list or tuple of field names (in the same format as list_display) to link.
list_display_links can specify one or many field names. As long as the field names appear in list_display, Django doesn’t care how many (or how few) fields are linked. The only requirement is: If you want to use list_display_links, you must define list_display.
In this example, the first_name and last_name fields will be linked on the change list page:
class Admin:
list_display = ('first_name', 'last_name', 'birthday')
list_display_links = ('first_name', 'last_name')
Finally, note that in order to use list_display_links, you must define list_display, too.
Set list_filter to activate filters in the right sidebar of the change list page of the admin. This should be a list of field names, and each specified field should be either a BooleanField, DateField, DateTimeField or ForeignKey.
This example, taken from the django.contrib.auth.models.User model, shows how both list_display and list_filter work:
class Admin:
list_display = ('username', 'email', 'first_name', 'last_name', 'is_staff')
list_filter = ('is_staff', 'is_superuser')
The above code results in an admin change list page that looks like this:
(This example also has search_fields defined. See below.)
Set list_per_page to control how many items appear on each paginated admin change list page. By default, this is set to 100.
Set ordering to specify how objects on the admin change list page should be ordered. This should be a list or tuple in the same format as a model’s ordering parameter.
If this isn’t provided, the Django admin will use the model’s default ordering.
Set save_as to enable a “save as” feature on admin change forms.
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 as” means the object will be saved as a new object (with a new ID), rather than the old object.
By default, save_as is set to False.
Set save_on_top to add save buttons across the top of your admin change forms.
Normally, the save buttons appear only at the bottom of the forms. If you set save_on_top, the buttons will appear both on the top and the bottom.
By default, save_on_top is set to False.
Set search_fields to enable a search box on the admin change list page. This should be set to a list of field names that will be searched whenever somebody submits a search query in that text box.
These fields should be some kind of text field, such as CharField or TextField.
When somebody does a search in the admin search box, Django splits the search query into words and returns all objects that contain each of the words, case insensitive, where each word must be in at least one of search_fields. For example, if search_fields is set to ['first_name', 'last_name'] and a user searches for john lennon, Django will do the equivalent of this SQL WHERE clause:
WHERE (first_name ILIKE '%john%' OR last_name ILIKE '%john%') AND (first_name ILIKE '%lennon%' OR last_name ILIKE '%lennon%')
A Manager is the interface through which database query operations are provided to Django models. At least one Manager exists for every model in a Django application.
The way Manager classes work is documented in the Retrieving objects section of the database API docs, but this section specifically touches on model options that customize Manager behavior.
By default, Django adds a Manager with the name objects to every Django model class. However, if you want to use objects as a field name, or if you want to use a name other than objects for the Manager, you can rename it on a per-model basis. To rename the Manager for a given class, define a class attribute of type models.Manager() on that model. For example:
from django.db import models
class Person(models.Model):
#...
people = models.Manager()
Using this example model, Person.objects will generate an AttributeError exception, but Person.people.all() will provide a list of all Person objects.
You can use a custom Manager in a particular model by extending the base Manager class and instantiating your custom Manager in your model.
There are two reasons you might want to customize a Manager: to add extra Manager methods, and/or to modify the initial QuerySet the Manager returns.
Adding extra Manager methods is the preferred way to add “table-level” functionality to your models. (For “row-level” functionality — i.e., functions that act on a single instance of a model object — use Model methods, not custom Manager methods.)
A custom Manager method can return anything you want. It doesn’t have to return a QuerySet.
For example, this custom Manager offers a method with_counts(), which returns a list of all OpinionPoll objects, each with an extra num_responses attribute that is the result of an aggregate query:
class PollManager(models.Manager):
def with_counts(self):
from django.db import connection
cursor = connection.cursor()
cursor.execute("""
SELECT p.id, p.question, p.poll_date, COUNT(*)
FROM polls_opinionpoll p, polls_response r
WHERE p.id = r.poll_id
GROUP BY 1, 2, 3
ORDER BY 3 DESC""")
result_list = []
for row in cursor.fetchall():
p = self.model(id=row[0], question=row[1], poll_date=row[2])
p.num_responses = row[3]
result_list.append(p)
return result_list
class OpinionPoll(models.Model):
question = models.CharField(maxlength=200)
poll_date = models.DateField()
objects = PollManager()
class Response(models.Model):
poll = models.ForeignKey(Poll)
person_name = models.CharField(maxlength=50)
response = models.TextField()
With this example, you’d use OpinionPoll.objects.with_counts() to return that list of OpinionPoll objects with num_responses attributes.
Another thing to note about this example is that Manager methods can access self.model to get the model class to which they’re attached.
A Manager‘s base QuerySet returns all objects in the system. For example, using this model:
class Book(models.Model):
title = models.CharField(maxlength=100)
author = models.CharField(maxlength=50)
…the statement Book.objects.all() will return all books in the database.
You can override a Manager‘s base QuerySet by overriding the Manager.get_query_set() method. get_query_set() should return a QuerySet with the properties you require.
For example, the following model has two Managers — one that returns all objects, and one that returns only the books by Roald Dahl:
# First, define the Manager subclass.
class DahlBookManager(models.Manager):
def get_query_set(self):
return super(DahlBookManager, self).get_query_set().filter(author='Roald Dahl')
# Then hook it into the Book model explicitly.
class Book(models.Model):
title = models.CharField(maxlength=100)
author = models.CharField(maxlength=50)
objects = models.Manager() # The default manager.
dahl_objects = DahlBookManager() # The Dahl-specific manager.
With this sample model, Book.objects.all() will return all books in the database, but Book.dahl_objects.all() will only return the ones written by Roald Dahl.
Of course, because get_query_set() returns a QuerySet object, you can use filter(), exclude() and all the other QuerySet methods on it. So these statements are all legal:
Book.dahl_objects.all() Book.dahl_objects.filter(title='Matilda') Book.dahl_objects.count()
This example also pointed out another interesting technique: using multiple managers on the same model. You can attach as many Manager() instances to a model as you’d like. This is an easy way to define common “filters” for your models.
For example:
class MaleManager(models.Manager):
def get_query_set(self):
return super(MaleManager, self).get_query_set().filter(sex='M')
class FemaleManager(models.Manager):
def get_query_set(self):
return super(FemaleManager, self).get_query_set().filter(sex='F')
class Person(models.Model):
first_name = models.CharField(maxlength=50)
last_name = models.CharField(maxlength=50)
sex = models.CharField(maxlength=1, choices=(('M', 'Male'), ('F', 'Female')))
people = models.Manager()
men = MaleManager()
women = FemaleManager()
This example allows you to request Person.men.all(), Person.women.all(), and Person.people.all(), yielding predictable results.
If you use custom Manager objects, take note that the first Manager Django encounters (in order by which they’re defined in the model) has a special status. Django interprets the first Manager defined in a class as the “default” Manager. Certain operations — such as Django’s admin site — use the default Manager to obtain lists of objects, so it’s generally a good idea for the first Manager to be relatively unfiltered. In the last example, the people Manager is defined first — so it’s the default Manager.
Define custom methods on a model to add custom “row-level” functionality to your objects. Whereas Manager methods are intended to do “table-wide” things, model methods should act on a particular model instance.
This is a valuable technique for keeping business logic in one place — the model.
For example, this model has a few custom methods:
class Person(models.Model):
first_name = models.CharField(maxlength=50)
last_name = models.CharField(maxlength=50)
birth_date = models.DateField()
address = models.CharField(maxlength=100)
city = models.CharField(maxlength=50)
state = models.USStateField() # Yes, this is America-centric...
def baby_boomer_status(self):
"Returns the person's baby-boomer status."
import datetime
if datetime.date(1945, 8, 1) <= self.birth_date <= datetime.date(1964, 12, 31):
return "Baby boomer"
if self.birth_date < datetime.date(1945, 8, 1):
return "Pre-boomer"
return "Post-boomer"
def is_midwestern(self):
"Returns True if this person is from the Midwest."
return self.state in ('IL', 'WI', 'MI', 'IN', 'OH', 'IA', 'MO')
def _get_full_name(self):
"Returns the person's full name."
return '%s %s' % (self.first_name, self.last_name)
full_name = property(_get_full_name)
The last method in this example is a property. Read more about properties.
A few object methods have special meaning:
__str__() is a Python “magic method” that defines what should be returned if you call str() on the object. Django uses str(obj) in a number of places, most notably as the value displayed to render an object in the Django admin site and as the value inserted into a template when it displays an object. Thus, you should always return a nice, human-readable string for the object’s __str__. Although this isn’t required, it’s strongly encouraged.
For example:
class Person(models.Model):
first_name = models.CharField(maxlength=50)
last_name = models.CharField(maxlength=50)
def __str__(self):
return '%s %s' % (self.first_name, self.last_name)
Define a get_absolute_url() method to tell Django how to calculate the URL for an object. For example:
def get_absolute_url(self):
return "/people/%i/" % self.id
Django uses this in its admin interface. If an object defines get_absolute_url(), the object-editing page will have a “View on site” link that will jump you directly to the object’s public view, according to get_absolute_url().
Also, a couple of other bits of Django, such as the syndication-feed framework, use get_absolute_url() as a convenience to reward people who’ve defined the method.
It’s good practice to use get_absolute_url() in templates, instead of hard-coding your objects’ URLs. For example, this template code is bad:
<a href="/people/{{ object.id }}/">{{ object.name }}</a>
But this template code is good:
<a href="{{ object.get_absolute_url }}">{{ object.name }}</a>
(Yes, we know get_absolute_url() couples URLs to models, which violates the DRY principle, because URLs are defined both in a URLconf and in the model. This is a rare case in which we’ve intentionally violated that principle for the sake of convenience. With that said, we’re working on an even cleaner way of specifying URLs in a more DRY fashion.)
Feel free to write custom SQL statements in custom model methods and module-level methods. The object django.db.connection represents the current database connection. To use it, call connection.cursor() to get a cursor object. Then, call cursor.execute(sql, [params]) to execute the SQL and cursor.fetchone() or cursor.fetchall() to return the resulting rows. Example:
def my_custom_sql(self):
from django.db import connection
cursor = connection.cursor()
cursor.execute("SELECT foo FROM bar WHERE baz = %s", [self.baz])
row = cursor.fetchone()
return row
connection and cursor simply use the standard Python DB-API. If you’re not familiar with the Python DB-API, note that the SQL statement in cursor.execute() uses placeholders, "%s", rather than adding parameters directly within the SQL. If you use this technique, the underlying database library will automatically add quotes and escaping to your parameter(s) as necessary. (Also note that Django expects the "%s" placeholder, not the "?" placeholder, which is used by the SQLite Python bindings. This is for the sake of consistency and sanity.)
A final note: If all you want to do is a custom WHERE clause, you can just just the where, tables and params arguments to the standard lookup API. See Other lookup options.
As explained in the database API docs, each model gets a few methods automatically — most notably, save() and delete(). You can override these methods to alter behavior.
A classic use-case for overriding the built-in methods is if you want something to happen whenever you save an object. For example:
class Blog(models.Model):
name = models.CharField(maxlength=100)
tagline = models.TextField()
def save(self):
do_something()
super(Blog, self).save() # Call the "real" save() method.
do_something_else()
You can also prevent saving:
class Blog(models.Model):
name = models.CharField(maxlength=100)
tagline = models.TextField()
def save(self):
if self.name == "Yoko Ono's blog":
return # Yoko shall never have her own blog!
else:
super(Blog, self).save() # Call the "real" save() method.
It’s perfectly OK to relate a model to one from another app. To do this, just import the related model at the top of the model that holds your model. Then, just refer to the other model class wherever needed. For example:
from mysite.geography.models import ZipCode
class Restaurant(models.Model):
# ...
zip_code = models.ForeignKey(ZipCode)
Once you have created your models, the final step is to tell Django you’re going to use those models.
Do this by editing your settings file and changing the INSTALLED_APPS setting to add the name of the module that contains your models.py.
For example, if the models for your application live in the module mysite.myapp.models (the package structure that is created for an application by the manage.py startapp script), INSTALLED_APPS should read, in part:
INSTALLED_APPS = (
#...
'mysite.myapp',
#...
)
Django provides a hook for passing the database arbitrary SQL that’s executed just after the CREATE TABLE statements. Use this hook, for example, if you want to populate default records, or create SQL functions, automatically.
The hook is simple: Django just looks for a file called <appname>/sql/<modelname>.sql, where <appname> is your app directory and <modelname> is the model’s name in lowercase.
In the Person example model at the top of this document, assuming it lives in an app called myapp, you could add arbitrary SQL to the file myapp/sql/person.sql. Here’s an example of what the file might contain:
INSERT INTO myapp_person (first_name, last_name) VALUES ('John', 'Lennon');
INSERT INTO myapp_person (first_name, last_name) VALUES ('Paul', 'McCartney');
Each SQL file, if given, is expected to contain valid SQL. The SQL files are piped directly into the database after all of the models’ table-creation statements have been executed.
The SQL files are read by the sqlinitialdata, sqlreset, sqlall and reset commands in manage.py. Refer to the manage.py documentation for more information.
Note that if you have multiple SQL data files, there’s no guarantee of the order in which they’re executed. The only thing you can assume is that, by the time your custom data files are executed, all the database tables already will have been created.
There’s also a hook for backend-specific SQL data. For example, you can have separate initial-data files for PostgreSQL and MySQL. For each app, Django looks for a file called <appname>/sql/<modelname>.<backend>.sql, where <appname> is your app directory, <modelname> is the model’s name in lowercase and <backend> is the value of DATABASE_ENGINE in your settings file (e.g., postgresql, mysql).
Backend-specific SQL data is executed before non-backend-specific SQL data. For example, if your app contains the files sql/person.sql and sql/person.postgresql.sql and you’re installing the app on PostgreSQL, Django will execute the contents of sql/person.postgresql.sql first, then sql/person.sql.
If you notice errors with this documentation, please open a ticket and let us know!
Please only use the ticket tracker for criticisms and improvements on the docs. For tech support, ask in the IRC channel or post to the django-users list.
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