General field options

The following arguments are available to all field types. All are optional.

null

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.

blank

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.

choices

A list 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.

core

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.

db_column

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.

db_index

If True, django-admin.py sqlindexes will output a CREATE INDEX statement for this field.

default

The default value for the field.

editable

If False, the field will not be editable in the admin. Default is True.

help_text

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.

primary_key

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 = meta.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.

radio_admin

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.

unique

If True, this field must be unique throughout the table.

This is enforced at the database level and at the Django admin-form level.

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.

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.

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.

validator_list

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.

Field types

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:

• The database column type (e.g. INTEGER, VARCHAR).
• The widget to use in Django's admin (e.g. <input type="text">, <select>).
• The minimal validation requirements, used in Django's admin and in manipulators.

Here are all available field types:

AutoField

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 primary_key in General field options above.)

BooleanField

A true/false field.

The admin represents this as a checkbox.

CharField

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.

CommaSeparatedIntegerField

A field of integers separated by commas. As in CharField, the maxlength argument is required.

DateField

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.
auto_now_add	Automatically set the field to now when the object is first created. Useful for creation of timestamps.

The admin represents this as an <input type="text"> with a JavaScript calendar and a shortcut for "Today."

DateTimeField

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.

EmailField

A CharField that checks that the value is a valid e-mail address. This doesn't accept maxlength.

FileField

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:

1. In your settings file, you'll need to define MEDIA_ROOT as the full path to a directory where you'd like Django to store uploaded files. (For performance, these files are not stored in the database.) Define MEDIA_URL as the base public URL of that directory. Make sure that this directory is writable by the Web server's user account.
2. Add the FileField or ImageField to your model, making sure to define the upload_to option to tell Django to which subdirectory of MEDIA_ROOT it should upload files.
3. All that will be stored in your database is a path to the file (relative to MEDIA_ROOT). You'll must likely want to use the convenience get_<fieldname>_url function provided by Django. For example, if your ImageField is called mug_shot, you can get the absolute URL to your image in a template with {{ object.get_mug_shot_url }}.

FilePathField

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).

FloatField

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:

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)

The admin represents this as an <input type="text"> (a single-line input).

ImageField

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.

IntegerField

An integer.

The admin represents this as an <input type="text"> (a single-line input).

IPAddressField

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).

NullBooleanField

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.

PhoneNumberField

A CharField that checks that the value is a valid U.S.A.-style phone number (in the format XXX-XXX-XXXX).

PositiveIntegerField

Like an IntegerField, but must be positive.

PositiveSmallIntegerField

Like a PositiveIntegerField, but only allows values under a certain (database-dependent) point.

SlugField

"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.

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, via JavaScript, in the object's admin form:

meta.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).

SmallIntegerField

Like an IntegerField, but only allows values under a certain (database-dependent) point.

TextField

A large text field.

The admin represents this as a <textarea> (a multi-line input).

TimeField

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.

URLField

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).

USStateField

A two-letter U.S. state abbreviation.

The admin represents this as an <input type="text"> (a single-line input).

XMLField

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.

Relationships

Clearly, the power of relational databases lies in relating tables to each other. Django offers ways to define the most common types of database relationships: Many-to-one, many-to-many and one-to-one.

class City(meta.Model):
    # ...

class Place(meta.Model):
    # ...
    city = meta.ForeignKey(City)

class Topping(meta.Model):
    # ...

class Pizza(meta.Model):
    # ...
    toppings = meta.ManyToManyField(Topping)

Module-level methods

Since each data class effectively turns into a "magic" Python module under django.models, 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 function:

class Pizza(meta.Model):
    # ...

    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 as the module scope. These methods do NOT have access to globals within your model's module.

Manipulator methods

Similarly, you can add methods to the object's manipulators by defining methods that being with "_manipulator_". This is most useful for providing custom validators for certain fields, because manipulators automatically call any method that begins with "validate":

class Pizza(meta.Model):
    # ...

    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."

Executing custom SQL

Feel free to write custom SQL statements in custom model methods and module-level methods. Each custom method automatically has access to the variable db, which is the current database connection. To use it, call db.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):
    cursor = db.cursor()
    cursor.execute("SELECT foo FROM bar WHERE baz = %s", [self.baz])
    row = cursor.fetchone()
    return row

If your custom SQL statement alters the data in your database -- for example, via a DELETE or UPDATE -- you'll need to call db.commit(). Example:

def my_custom_sql2(self):
    cursor = db.cursor()
    cursor.execute("DELETE FROM bar WHERE baz = %s", [self.baz])
    db.commit()

db 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.