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Django 3.0
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モデルフィールドリファレンス

このドキュメントには、Django が提供する field options と field types を含む、Field の全ての API リファレンスが記載されています。

フィールドオプション

以下の引数は全てのフィールドタイプで有効です。全て省略可能です。

null

Field.null

True``の場合、Django はデータベース内に ``NULL として空の値を保持します。デフォルトは False です。

Avoid using null on string-based fields such as CharField and TextField. 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;" the Django convention is to use the empty string, not NULL. One exception is when a CharField has both unique=True and blank=True set. In this situation, null=True is required to avoid unique constraint violations when saving multiple objects with blank values.

文字列ベースと非文字列ベースのフィールドのどちらでも、フォーム内で空の値を許容したい場合には、blank=True をセットすることも必要となります。これは、null パラメータはデータベーストレー時のみに影響するためです (blank を参照してください)。

blank

Field.blank

True の場合、フィールドはブランクになることが許容されます。デフォルトは False です。

null とは異なる点に注意してください。null が純粋にデータベースに関連する一方で、blank はバリデーションに関連します。フィールドが blank=True を持つ場合、フォームバリデーションは空の値のエントリーを許容します。blank=False を持つ場合、フィールドは必須となります。

choices

Field.choices

A sequence consisting itself of iterables of exactly two items (e.g. [(A, B), (A, B) ...]) to use as choices for this field. If choices are given, they're enforced by model validation and the default form widget will be a select box with these choices instead of the standard text field.

各タプルの最初の要素は、モデル上でセットするための実際の値です。2 番目の要素は人間が読むための名前です。例えば:

Code
YEAR_IN_SCHOOL_CHOICES = [
    ('FR', 'Freshman'),
    ('SO', 'Sophomore'),
    ('JR', 'Junior'),
    ('SR', 'Senior'),
    ('GR', 'Graduate'),
]

一般的に、モデルクラスの内部で選択肢を定義し、それぞれの値に適切に名前づけられた定数を定義するのがベストです:

Code
from django.db import models

class Student(models.Model):
    FRESHMAN = 'FR'
    SOPHOMORE = 'SO'
    JUNIOR = 'JR'
    SENIOR = 'SR'
    GRADUATE = 'GR'
    YEAR_IN_SCHOOL_CHOICES = [
        (FRESHMAN, 'Freshman'),
        (SOPHOMORE, 'Sophomore'),
        (JUNIOR, 'Junior'),
        (SENIOR, 'Senior'),
        (GRADUATE, 'Graduate'),
    ]
    year_in_school = models.CharField(
        max_length=2,
        choices=YEAR_IN_SCHOOL_CHOICES,
        default=FRESHMAN,
    )

    def is_upperclass(self):
        return self.year_in_school in {self.JUNIOR, self.SENIOR}

Though you can define a choices list outside of a model class and then refer to it, defining the choices and names for each choice inside the model class keeps all of that information with the class that uses it, and helps reference the choices (e.g, Student.SOPHOMORE will work anywhere that the Student model has been imported).

組織化する目的に使用できる、名前付きグループに利用可能な選択肢を収集することもできます。

Code
MEDIA_CHOICES = [
    ('Audio', (
            ('vinyl', 'Vinyl'),
            ('cd', 'CD'),
        )
    ),
    ('Video', (
            ('vhs', 'VHS Tape'),
            ('dvd', 'DVD'),
        )
    ),
    ('unknown', 'Unknown'),
]

The first element in each tuple is the name to apply to the group. The second element is an iterable of 2-tuples, with each 2-tuple containing a value and a human-readable name for an option. Grouped options may be combined with ungrouped options within a single list (such as the 'unknown' option in this example).

choices がセットされているモデルフィールドごとに、Django はフィールドの現在の値に対して人間が読める名前を取得するメソッドを追加します。データベース API ドキュメントの get_FOO_display() を参照してください。

Note that choices can be any sequence 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.

blank=False が default とともにフィールド上にセットされない限り、"---------" を含むラベルがセレクトボックスに表示されます。この動作をオーバーライドするためには、None を含む choices にタプルを追加してください; 例えば (None, '表示専用の文字列'). もしくは、None の代わりに空の文字列を使うこともできます。これは特に CharField などに適しています。

Enumeration types

In addition, Django provides enumeration types that you can subclass to define choices in a concise way:

Code
from django.utils.translation import gettext_lazy as _

class Student(models.Model):

    class YearInSchool(models.TextChoices):
        FRESHMAN = 'FR', _('Freshman')
        SOPHOMORE = 'SO', _('Sophomore')
        JUNIOR = 'JR', _('Junior')
        SENIOR = 'SR', _('Senior')
        GRADUATE = 'GR', _('Graduate')

    year_in_school = models.CharField(
        max_length=2,
        choices=YearInSchool.choices,
        default=YearInSchool.FRESHMAN,
    )

    def is_upperclass(self):
        return self.year_in_school in {
            self.YearInSchool.JUNIOR,
            self.YearInSchool.SENIOR,
        }

These work similar to enum from Python's standard library, but with some modifications:

  • Enum member values are a tuple of arguments to use when constructing the concrete data type. Django supports adding an extra string value to the end of this tuple to be used as the human-readable name, or label. The label can be a lazy translatable string. Thus, in most cases, the member value will be a (value, label) two-tuple. See below for an example of subclassing choices using a more complex data type. If a tuple is not provided, or the last item is not a (lazy) string, the label is automatically generated from the member name.

  • A .label property is added on values, to return the human-readable name.

  • A number of custom properties are added to the enumeration classes -- .choices, .labels, .values, and .names -- to make it easier to access lists of those separate parts of the enumeration. Use .choices as a suitable value to pass to choices in a field definition.

  • The use of enum.unique() is enforced to ensure that values cannot be defined multiple times. This is unlikely to be expected in choices for a field.

Note that using YearInSchool.SENIOR, YearInSchool['SENIOR'], or YearInSchool('SR') to access or lookup enum members work as expected, as do the .name and .value properties on the members.

If you don't need to have the human-readable names translated, you can have them inferred from the member name (replacing underscores with spaces and using title-case):

Code
>>> class Vehicle(models.TextChoices):
...     CAR = 'C'
...     TRUCK = 'T'
...     JET_SKI = 'J'
...
>>> Vehicle.JET_SKI.label
'Jet Ski'

Since the case where the enum values need to be integers is extremely common, Django provides an IntegerChoices class. For example:

Code
class Card(models.Model):

    class Suit(models.IntegerChoices):
        DIAMOND = 1
        SPADE = 2
        HEART = 3
        CLUB = 4

    suit = models.IntegerField(choices=Suit.choices)

It is also possible to make use of the Enum Functional API with the caveat that labels are automatically generated as highlighted above:

Code
>>> MedalType = models.TextChoices('MedalType', 'GOLD SILVER BRONZE')
>>> MedalType.choices
[('GOLD', 'Gold'), ('SILVER', 'Silver'), ('BRONZE', 'Bronze')]
>>> Place = models.IntegerChoices('Place', 'FIRST SECOND THIRD')
>>> Place.choices
[(1, 'First'), (2, 'Second'), (3, 'Third')]

If you require support for a concrete data type other than int or str, you can subclass Choices and the required concrete data type, e.g. date for use with DateField:

Code
class MoonLandings(datetime.date, models.Choices):
    APOLLO_11 = 1969, 7, 20, 'Apollo 11 (Eagle)'
    APOLLO_12 = 1969, 11, 19, 'Apollo 12 (Intrepid)'
    APOLLO_14 = 1971, 2, 5, 'Apollo 14 (Antares)'
    APOLLO_15 = 1971, 7, 30, 'Apollo 15 (Falcon)'
    APOLLO_16 = 1972, 4, 21, 'Apollo 16 (Orion)'
    APOLLO_17 = 1972, 12, 11, 'Apollo 17 (Challenger)'

There are some additional caveats to be aware of:

  • Enumeration types do not support named groups.

  • Because an enumeration with a concrete data type requires all values to match the type, overriding the blank label cannot be achieved by creating a member with a value of None. Instead, set the __empty__ attribute on the class:

    Code
    class Answer(models.IntegerChoices):
    NO = 0, _('No')
    YES = 1, _('Yes')

    __empty__ = _('(Unknown)')

db_column

Field.db_column

このフィールドを使用するためのデータベースのカラムの名前です。もし与えられなければ、Django はフィールド名を使用します。

データベースのカラム名が SQL の予約語だったり、Python の変数名として使用できない文字 (特に多いのがハイフン) が含まれていたとしても大丈夫です。Django はカラムとテーブルの名前を自動的にクオートして処理してくれます。

db_index

Field.db_index

True の場合、データベースインデックスがこのフィールドのために生成されます。

db_tablespace

Field.db_tablespace

The name of the database tablespace to use for this field's index, if this field is indexed. The default is the project's DEFAULT_INDEX_TABLESPACE setting, if set, or the db_tablespace of the model, if any. If the backend doesn't support tablespaces for indexes, this option is ignored.

default

Field.default

そのフィールドのデフォルト値です。このオプションには特定の値もしくは呼び出し可能オブジェクトを渡すことができます。もし渡した値が呼び出し可能であれば新しくオブジェクトが生成される度に呼び出されます。

The default can't be a mutable object (model instance, list, set, etc.), as a reference to the same instance of that object would be used as the default value in all new model instances. Instead, wrap the desired default in a callable. For example, if you want to specify a default dict for JSONField, use a function:

Code
def contact_default():
    return {"email": "to1@example.com"}

contact_info = JSONField("ContactInfo", default=contact_default)

lambdas can't be used for field options like default because they can't be serialized by migrations. See that documentation for other caveats.

For fields like ForeignKey that map to model instances, defaults should be the value of the field they reference (pk unless to_field is set) instead of model instances.

The default value is used when new model instances are created and a value isn't provided for the field. When the field is a primary key, the default is also used when the field is set to None.

editable

Field.editable

If False, the field will not be displayed in the admin or any other ModelForm. They are also skipped during model validation. Default is True.

error_messages

Field.error_messages

The error_messages argument lets you override the default messages that the field will raise. Pass in a dictionary with keys matching the error messages you want to override.

Error message keys include null, blank, invalid, invalid_choice, unique, and unique_for_date. Additional error message keys are specified for each field in the Field types section below.

These error messages often don't propagate to forms. See モデルの error_messages のレンダリングを考える.

help_text

Field.help_text

フォームウィジェットと共に表示される "補助" テキストになります。この値はフィールドがフォームとして利用されない場合でもドキュメント化する際に有用です。

Note that this value is not HTML-escaped in automatically-generated forms. This lets you include HTML in help_text if you so desire. For example:

Code
help_text="Please use the following format: <em>YYYY-MM-DD</em>."

Alternatively you can use plain text and django.utils.html.escape() to escape any HTML special characters. Ensure that you escape any help text that may come from untrusted users to avoid a cross-site scripting attack.

primary_key

Field.primary_key

True の場合、設定したフィールドはそのモデルの主キーとなります。

If you don't specify primary_key=True for any field in your model, Django will automatically add an AutoField to hold the primary key, so you don't need to set primary_key=True on any of your fields unless you want to override the default primary-key behavior. For more, see 自動インクリメントのプライマリーキーフィールド.

primary_key=True implies null=False and unique=True. Only one primary key is allowed on an object.

The primary key field is read-only. If you change the value of the primary key on an existing object and then save it, a new object will be created alongside the old one.

unique

Field.unique

True の場合、そのフィールドはテーブル上で一意となる制約を受けます。

This is enforced at the database level and by model validation. If you try to save a model with a duplicate value in a unique field, a django.db.IntegrityError will be raised by the model's save() method.

This option is valid on all field types except ManyToManyField and OneToOneField.

Note that when unique is True, you don't need to specify db_index, because unique implies the creation of an index.

unique_for_date

Field.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.

Note that if you set this to point to a DateTimeField, only the date portion of the field will be considered. Besides, when USE_TZ is True, the check will be performed in the current time zone at the time the object gets saved.

This is enforced by Model.validate_unique() during model validation but not at the database level. If any unique_for_date constraint involves fields that are not part of a ModelForm (for example, if one of the fields is listed in exclude or has editable=False), Model.validate_unique() will skip validation for that particular constraint.

unique_for_month

Field.unique_for_month

Like unique_for_date, but requires the field to be unique with respect to the month.

unique_for_year

Field.unique_for_year

Like unique_for_date and unique_for_month.

verbose_name

Field.verbose_name

A human-readable name for the field. If the verbose name isn't given, Django will automatically create it using the field's attribute name, converting underscores to spaces. See Verbose field names.

validators

Field.validators

A list of validators to run for this field. See the validators documentation for more information.

Registering and fetching lookups

Field implements the lookup registration API. The API can be used to customize which lookups are available for a field class, and how lookups are fetched from a field.

フィールドの型

AutoField

class AutoField(**options)

利用可能な ID に応じて、自動的にインクリメントする IntegerField です。通常は直接使う必要はありません; 指定しない場合は、主キーのフィールドが自動的にモデルに追加されます。自動インクリメントのプライマリーキーフィールド も参照してください。

BigAutoField

class BigAutoField(**options)

64 ビットの数値です。1 から 9223372036854775807 までの数を扱える以外は、AutoField と同じです。

BigIntegerField

class BigIntegerField(**options)

A 64-bit integer, much like an IntegerField except that it is guaranteed to fit numbers from -9223372036854775808 to 9223372036854775807. The default form widget for this field is a NumberInput.

BinaryField

class BinaryField(max_length=None, **options)

A field to store raw binary data. It can be assigned bytes, bytearray, or memoryview.

By default, BinaryField sets editable to False, in which case it can't be included in a ModelForm.

BinaryField has one extra optional argument:

BinaryField.max_length

The maximum length (in characters) of the field. The maximum length is enforced in Django's validation using MaxLengthValidator.

BooleanField

class BooleanField(**options)

true/false のフィールドです。

The default form widget for this field is CheckboxInput, or NullBooleanSelect if null=True.

Field.default が定義されていないときの BooleanField のデフォルト値は None です。

CharField

class CharField(max_length=None, **options)

小 - 大サイズの文字列のフィールドです。

多量のテキストを扱うときは TextField を使ってください。

このフィールドのデフォルトのフォームウィジェットは TextInput です。

CharField には追加的な必須の引数があります:

CharField.max_length

The maximum length (in characters) of the field. The max_length is enforced at the database level and in Django's validation using MaxLengthValidator.

DateField

class DateField(auto_now=False, auto_now_add=False, **options)

Python で datetime.date インスタンスによって表される日付です。多少の追加的な省略可能な引数を持ちます:

DateField.auto_now

オブジェクトが保存される度に自動的に現在の日付をセットします。"最後の変更" タイムスタンプに役立ちます。現在の日付が常に使われる点に注意してください; オーバーライドできる単なるデフォルト値ではありません。

Model.save() が呼ばれたとき、フィールドは自動的に更新されるだけです。QuerySet.update() のような別の方法で他のフィールドに更新を加えるとき、フィールドは更新されません。あのように更新の中でフィールドの独自の値を指定できるとしてもです。

DateField.auto_now_add

オブジェクトが最初に作成されるとき、自動的にフィールドに現在の日付をセットします。タイムスタンプの作成に役立ちます。現在の日付が 常に 使われる点に注意してください; オーバーライドできる単なるデフォルト値ではありません。たとえオブジェクトを作成するときに値をセットしたとしても無視されます。このフィールドを修正できるようにしておきたい場合は、auto_now_add=True の代わりに以下をセットしてください:

The default form widget for this field is a DateInput. The admin adds a JavaScript calendar, and a shortcut for "Today". Includes an additional invalid_date error message key.

オプション auto_now_add、auto_now、default` は相互に排他的です。これらのオプションを組み合わせるとエラーが発生します。

DateTimeField

class DateTimeField(auto_now=False, auto_now_add=False, **options)

Python で datetime.datetime インスタンスによって表される日付と時刻です。DateField と同じくいくつかの追加的な引数を持ちます:

The default form widget for this field is a single DateTimeInput. The admin uses two separate TextInput widgets with JavaScript shortcuts.

DecimalField

class DecimalField(max_digits=None, decimal_places=None, **options)

A fixed-precision decimal number, represented in Python by a Decimal instance. It validates the input using DecimalValidator.

Has two required arguments:

DecimalField.max_digits

数値内で使える桁数の最大値です。 decimal_places 以上でなければならない点に注意してください。

DecimalField.decimal_places

数値とともに保持される小数点以下の位の数です。

例えば、小数点以下第2位の精度で 999 までの数値を保持するためには、以下を指定します:

Code
models.DecimalField(..., max_digits=5, decimal_places=2)

小数点以下第10位の精度で約10億までを保持するには:

Code
models.DecimalField(..., max_digits=19, decimal_places=10)

このフィールドのデフォルトのフォームウィジェットは、localize が False のとき NumberInput で、そうでなければ TextInput となります。

DurationField

class DurationField(**options)

時刻の期間を保持するフィールドで、 Python の timedelta によってモデル化されます。PostgreSQL で使われるときに用いられるデータ型は interval で、Oracle でのデータ型は INTERVAL DAY(9) TO SECOND(6)``です。 それ以外では、マイクロ秒の ``bigint が使われます。

EmailField

class EmailField(max_length=254, **options)

A CharField that checks that the value is a valid email address using EmailValidator.

FileField

class FileField(upload_to=None, max_length=100, **options)

ファイルアップロードのフィールドです。

2 つの省略可能な引数があります:

FileField.upload_to

この属性は、アップロードディレクトリとファイル名を設定する方法を提供し、2 つの方法でセットできます。どちらの場合も、値は Storage.save() メソッドに渡されます。

If you specify a string value or a Path, it 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). For example:

Code
class MyModel(models.Model):
    # file will be uploaded to MEDIA_ROOT/uploads
    upload = models.FileField(upload_to='uploads/')
    # or...
    # file will be saved to MEDIA_ROOT/uploads/2015/01/30
    upload = models.FileField(upload_to='uploads/%Y/%m/%d/')

If you are using the default FileSystemStorage, the string value will be appended to your MEDIA_ROOT path to form the location on the local filesystem where uploaded files will be stored. If you are using a different storage, check that storage's documentation to see how it handles upload_to.

upload_to may also be a callable, such as a function. This will be called to obtain the upload path, including the filename. This callable must accept two arguments and return a Unix-style path (with forward slashes) to be passed along to the storage system. The two arguments are:

Argument

説明

instance

An instance of the model where the FileField is defined. More specifically, this is the particular instance where the current file is being attached.

In most cases, this object will not have been saved to the database yet, so if it uses the default AutoField, it might not yet have a value for its primary key field.

filename

The filename that was originally given to the file. This may or may not be taken into account when determining the final destination path.

例:

Code
def user_directory_path(instance, filename):
    # file will be uploaded to MEDIA_ROOT/user_<id>/<filename>
    return 'user_{0}/{1}'.format(instance.user.id, filename)

class MyModel(models.Model):
    upload = models.FileField(upload_to=user_directory_path)
FileField.storage

A storage object, which handles the storage and retrieval of your files. See ファイルの管理 for details on how to provide this object.

このフィールドのデフォルトのフォームウィジェットは ClearableFileInput です。

モデル内で a FileField や ImageField (後述) 使うにはいくつかのステップを取ります:

  1. 設定ファイル内で MEDIA_ROOT を指定します。この値は、Django がアップロードされたファイルを置く場所にします (パフォーマン ス上の理由から、ファイルをデータベースに置くことはありません)。 MEDIA_URL をそのディレクトリの公開 URL にします。ディレク トリは Web サーバのユーザアカウントに対して書き込み可能にしておかねばなりません。

  2. Add the FileField or ImageField to your model, defining the upload_to option to specify a subdirectory of MEDIA_ROOT to use for uploaded files.

  3. All that will be stored in your database is a path to the file (relative to MEDIA_ROOT). You'll most likely want to use the convenience url attribute provided by Django. For example, if your ImageField is called mug_shot, you can get the absolute path to your image in a template with {{ object.mug_shot.url }}.

For example, say your MEDIA_ROOT is set to '/home/media', and upload_to is set to 'photos/%Y/%m/%d'. The '%Y/%m/%d' part of upload_to is strftime() formatting; '%Y' is the four-digit year, '%m' is the two-digit month and '%d' is the two-digit day. If you upload a file on Jan. 15, 2007, it will be saved in the directory /home/media/photos/2007/01/15.

If you wanted to retrieve the uploaded file's on-disk filename, or the file's size, you could use the name and size attributes respectively; for more information on the available attributes and methods, see the File class reference and the ファイルの管理 topic guide.

The uploaded file's relative URL can be obtained using the url attribute. Internally, this calls the url() method of the underlying Storage class.

Note that whenever you deal with uploaded files, you should pay close attention to where you're uploading them and what type of files they are, to avoid security holes. Validate all uploaded files so that you're sure the files are what you think they are. For example, if you blindly let somebody upload files, without validation, to a directory that's within your Web server's document root, then somebody could upload a CGI or PHP script and execute that script by visiting its URL on your site. Don't allow that.

Also note that even an uploaded HTML file, since it can be executed by the browser (though not by the server), can pose security threats that are equivalent to XSS or CSRF attacks.

FileField instances are created in your database as varchar columns with a default max length of 100 characters. As with other fields, you can change the maximum length using the max_length argument.

FileField と FieldFile

class FieldFile

モデル上の FileField にアクセスするとき、元となるファイルにアアクセスするためのプロキシとして、FieldFile のインスタンスが与えられます。

FieldFile の API は File の API を反映していますが、主な違いが 1 つあります: クラスによってラップされたオブジェクトは必ずしも Python のビルトインのファイルオブジェクトのラッパーであるとは限りません。 代わりに、Storage.open() メソッドの結果を包むラッパーで、これは File オブジェクトもしくは File API の独自ストレージの実装となります。

In addition to the API inherited from File such as read() and write(), FieldFile includes several methods that can be used to interact with the underlying file:

FieldFile.name

関連する FileField の Storage のルートからの相対パスを含むファイル名です。

FieldFile.size

元となる Storage.size() メソッドの結果です。

FieldFile.url

元となる Storage クラス の url() メソッドを呼ぶことによって、ファイルの相対 URL にアクセスするための読み取り専用プロパティです。

FieldFile.open(mode='rb')

このインスタンスに関連付けられたファイルを、指定された モード で開くか、開き直します。標準の Python の open() メソッドとは違い、ファイルのデスクリプタを返しません。

元となるファイルはアクセスするときに暗黙的に開かれるので、元となるファイルにポインタをリセットするためか モード を変更するため以外には、このメソッドを呼ぶ必要はないでしょう。

FieldFile.close()

標準の Python の file.close() メソッドのように動作し、このインスタンスに関連付けられたファイルを閉じます。

FieldFile.save(name, content, save=True)

このメソッドは、ファイル名とファイルの内容を取り、それらをフィールドのストレージクラスに渡し、格納されたファイルをモデルフィールドに関連付けます。 手動でファイルデータをモデル上の FileField インスタンスに関連付けるには、save() メソッドを使用してそのファイルデータを保持します。

2 つの必要な引数をとります: name はファイルの名前で、content はファイルの内容を含むオブジェクトです。 省略可能な save 引数は、このフィールドに関連付けられたファイルが変更された後にモデルインスタンスが保存されるかどうかをコントロールします。 デフォルトは True です。

content 引数は、Python のビルトインのファイルオブジェクトではなく、django.core.files.File のインスタンスでなければならないことに注意してください。 以下のように、既存の Python ファイルオブジェクトから File を構築することができます:

Code
from django.core.files import File
# Open an existing file using Python's built-in open()
f = open('/path/to/hello.world')
myfile = File(f)

もしくは、以下のように Python の文字列から構築することもできます:

Code
from django.core.files.base import ContentFile
myfile = ContentFile("hello world")

より詳しくは ファイルの管理 をご覧ください。

FieldFile.delete(save=True)

このインスタンスに関連付けられているファイルを削除し、フィールドのすべての属性をクリアします。 注: このメソッドは、delete() が呼び出されたときにファイルが開いた場合、ファイルを閉じます。

省略可能な save 引数は、このフィールドに関連付けられたファイルが削除された後にモデルインスタンスを保存するかどうかをコントロールします。 デフォルトは True です。

モデルを削除するとき、関連ファイルは削除されない点に注意してください。 孤立したファイルをクリーンアップする必要がある場合、自分で処理する必要があります (例えば、手動で実行したり、例えば cron などを通して定期的に実行される、独自の管理コマンドです)。

FilePathField

class FilePathField(path='', match=None, recursive=False, allow_files=True, allow_folders=False, max_length=100, **options)

A CharField whose choices are limited to the filenames in a certain directory on the filesystem. Has some special arguments, of which the first is required:

FilePathField.path

必須です。FilePathField が選択肢から取得するディレクトリへの、ファイルシステムの絶対パスです。例: "/home/images"。

path may also be a callable, such as a function to dynamically set the path at runtime. Example:

Code
import os
from django.conf import settings
from django.db import models

def images_path():
    return os.path.join(settings.LOCAL_FILE_DIR, 'images')

class MyModel(models.Model):
    file = models.FilePathField(path=images_path)
FilePathField.match

省略可能です。正規表現で、文字列として、FilePathField がファイル名をフィルタリングするために使用します。 正規表現は、フルパスではなくベースファイル名に適用される点に注意してください。 例: "foo.*\.txt$"。これは foo23.txt とは合致しますが、bar.txt や foo23.png とは合致しません。

FilePathField.recursive

省略可能です。True か False のどちらかを取り、デフォルトは False です。path の全てのサブディレクトリを含むかどうかを指定します。

FilePathField.allow_files

省略可能です。True か False を取り、デフォルトは True です。指定された場所にあるファイルを含むかどうかを指定します。 これか allow_folders のどちらかを True にする必要があります。

FilePathField.allow_folders

省略可能です。True か False を取り、デフォルトは False です。指定した場所にあるフォルダーを含むかどうかを指定します。これか allow_files のどちらかを True にする必要があります。

もちろん、これらの引数は同時に使うことができます。

1つの可能性は、フルパスではなく、ベースファイル名に match が適用されることです。 したがって、この例:

Code
FilePathField(path="/home/images", match="foo.*", recursive=True)

...は、/home/images/foo/bar.png ではなく /home/images/foo.png とマッチします。これは、match がベースのファイル名に適用されるからです (foo.png と bar.png)。

FilePathField のインスタンスは、デフォルトが最大 100 文字の varchar カラムとして、データベース上に生成されます。他のフィールドと同様に、max_length 引数を使って最大文字数を変更することができます。

FloatField

class FloatField(**options)

float インスタンスによって表される Python の浮動小数点数です。

このフィールドのデフォルトのフォームウィジェットは、localize が False のとき NumberInput で、そうでなければ TextInput となります。

ImageField

class ImageField(upload_to=None, height_field=None, width_field=None, max_length=100, **options)

FileField から全ての属性とメソッドを継承して、さらにアップロードされたオブジェクトが有効な画像であることを検証します。

FileField で使える専用の属性に加えて、ImageField には height と width 属性があります。

これらの属性の照会を容易にするために、ImageField には 2 つの追加的な省略可能な引数があります:

ImageField.height_field

モデルインスタンスが保存される度に画像の高さで自動入力される、モデルフィールドの名前です。

ImageField.width_field

モデルインスタンスが保存される度に画像の幅で自動入力される、モデルフィールドの名前です。

Pillow ライブラリを必要とします。

ImageField のインスタンスは、デフォルトが最大 100 文字の varchar カラムとして、データベース上に生成されます。他のフィールドと同様に、max_length 引数を使って最大文字数を変更することができます。

このフィールドのデフォルトのフォームウィジェットは ClearableFileInput です。

IntegerField

class IntegerField(**options)

An integer. Values from -2147483648 to 2147483647 are safe in all databases supported by Django.

It uses MinValueValidator and MaxValueValidator to validate the input based on the values that the default database supports.

このフィールドのデフォルトのフォームウィジェットは、localize が False のとき NumberInput で、そうでなければ TextInput となります。

GenericIPAddressField

class GenericIPAddressField(protocol='both', unpack_ipv4=False, **options)

IPv4 か IPv6 のアドレスで、文字列フォーマットです (例: 192.0.2.30 ないし 2a02:42fe::4)。このフィールドのデフォルトのフォームウィジェットは TextInput です。

IPv6 アドレスは、 RFC 4291 Section 2.2 section 2.2 (同セクションの paragraph 3 で提案された IPv4 のフォーマットの使用を含む) にしたがって、 ::ffff:192.0.2.0 のように正規化します。たとえば、 2001:0::0:01 は 2001::1 と正規化され、 ::ffff:0a0a:0a0a は ::ffff:10.10.10.10 と正規化されます。そして、すべての文字は小文字に変換されます。

GenericIPAddressField.protocol

有効なインプットを、指定したプロトコルに制限します。 使用可能な値は 'both' (デフォルト)、'IPv4'、'IPv6' のどれかです。マッチングは大文字と小文字を区別しません。

GenericIPAddressField.unpack_ipv4

IPv4 にマッピングされた ::ffff:192.0.2.1 のようなアドレスをアンパックします。このオプションを有効にすると、このアドレスは 192.0.2.1 とアンパックされます。デフォルトは無効です。protocol が 'both' に設定されている場合にだけ使用できます。

ブランク値を要する場合、ブランク値は null として保持されるため、null 値を許容する必要があります。

NullBooleanField

class NullBooleanField(**options)

Like BooleanField with null=True. Use that instead of this field as it's likely to be deprecated in a future version of Django.

PositiveIntegerField

class PositiveIntegerField(**options)

IntegerField とほぼ同じですが、正の値かゼロ (0) でなければなりません。Django によってサポートされる全てのデータベースで、0 から 2147483647 までの値は安全です。後方互換性の理由から、値 0 が有効となっています。

PositiveSmallIntegerField

class PositiveSmallIntegerField(**options)

PositiveIntegerField とほぼ同じですが、特定の (データベースに依存した) ポイントより下の値のみを許容します。Django でサポートされている全てのデータベースで、0 から 32767 までの値は安全です。

SlugField

class SlugField(max_length=50, **options)

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.

CharField のように、max_length を指定することもできます (データベースの可搬性についてのノートとそのセクションの max_length も参照してください)。max_length が指定されていないとき、Django はデフォルトの文字数 50 を使います。

暗黙的に Field.db_index を True にセットします。

It is often useful to automatically prepopulate a SlugField based on the value of some other value. You can do this automatically in the admin using prepopulated_fields.

It uses validate_slug or validate_unicode_slug for validation.

SlugField.allow_unicode

If True, the field accepts Unicode letters in addition to ASCII letters. Defaults to False.

SmallAutoField

class SmallAutoField(**options)

Like an AutoField, but only allows values under a certain (database-dependent) limit. Values from 1 to 32767 are safe in all databases supported by Django.

SmallIntegerField

class SmallIntegerField(**options)

IntegerField とほぼ同じですが、特定の (データベースに依存した) ポイントより下の値のみを許容します。Django でサポートされている全てのデータベースで、-32768 から 32767 までの値は安全です。

TextField

class TextField(**options)

多量のテキストのフィールドです。このフィールドのデフォルトのフォームウィジェットは Textarea です。

max_length 属性を指定した場合、自動生成されたフォームフィールドの Textarea ウィジェット内で反映されます。ただし、モデルやデータベースのレベルでは施行されません。そのためには CharField を使用してください。

TimeField

class TimeField(auto_now=False, auto_now_add=False, **options)

Python で datetime.time インスタンスによって表される時刻です。DateField と同じ自動入力されるオプションを受け入れます。

The default form widget for this field is a TimeInput. The admin adds some JavaScript shortcuts.

URLField

class URLField(max_length=200, **options)

A CharField for a URL, validated by URLValidator.

The default form widget for this field is a URLInput.

全ての CharField サブクラスと同じく、URLField は省略可能な max_length 引数を取ります。max_length を指定しない場合、デフォルトの 200 が使われます。

UUIDField

class UUIDField(**options)

UUID (Universally Unique Identifier) を保持するためのフィールドです。Python's UUID クラスを使います。 PostgreSQL 上で使われるとき、uuid データ型の中に保持します。それ以外は char(32) の中に保持します。

UUID は attr:~Field.primary_key に代わる AutoField への良い選択肢です。 データベースはあなたのための UUID を生成しないため、default を使うことが推奨されます:

Code
import uuid
from django.db import models

class MyUUIDModel(models.Model):
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    # other fields

Callable (括弧が省略されている場合) は UUID のインスタンスではなく、default に渡されます。

リレーションシップフィールド

Djangoは、リレーションを表すフィールドのセットも定義しています。

ForeignKey

class ForeignKey(to, on_delete, **options)

A many-to-one relationship. Requires two positional arguments: the class to which the model is related and the on_delete option.

To create a recursive relationship -- an object that has a many-to-one relationship with itself -- use models.ForeignKey('self', on_delete=models.CASCADE).

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:

Code
from django.db import models

class Car(models.Model):
    manufacturer = models.ForeignKey(
        'Manufacturer',
        on_delete=models.CASCADE,
    )
    # ...

class Manufacturer(models.Model):
    # ...
    pass

Relationships defined this way on abstract models are resolved when the model is subclassed as a concrete model and are not relative to the abstract model's app_label:

products/models.py
Python
from django.db import models

class AbstractCar(models.Model):
    manufacturer = models.ForeignKey('Manufacturer', on_delete=models.CASCADE)

    class Meta:
        abstract = True
production/models.py
Python
from django.db import models
from products.models import AbstractCar

class Manufacturer(models.Model):
    pass

class Car(AbstractCar):
    pass

# Car.manufacturer will point to `production.Manufacturer` here.

To refer to models defined in another application, you can explicitly specify a model with the full application label. For example, if the Manufacturer model above is defined in another application called production, you'd need to use:

Code
class Car(models.Model):
    manufacturer = models.ForeignKey(
        'production.Manufacturer',
        on_delete=models.CASCADE,
    )

This sort of reference, called a lazy relationship, can be useful when resolving circular import dependencies between two applications.

A database index is automatically created on the ForeignKey. You can disable this by setting db_index to False. You may want to avoid the overhead of an index if you are creating a foreign key for consistency rather than joins, or if you will be creating an alternative index like a partial or multiple column index.

Database Representation

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) 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.

引数

ForeignKey accepts other arguments that define the details of how the relation works.

ForeignKey.on_delete

When an object referenced by a ForeignKey is deleted, Django will emulate the behavior of the SQL constraint specified by the on_delete argument. For example, if you have a nullable ForeignKey and you want it to be set null when the referenced object is deleted:

Code
user = models.ForeignKey(
    User,
    models.SET_NULL,
    blank=True,
    null=True,
)

on_delete doesn't create an SQL constraint in the database. Support for database-level cascade options may be implemented later.

The possible values for on_delete are found in django.db.models:

  • CASCADE

    Cascade deletes. Django emulates the behavior of the SQL constraint ON DELETE CASCADE and also deletes the object containing the ForeignKey.

    Model.delete() isn't called on related models, but the pre_delete and post_delete signals are sent for all deleted objects.

  • PROTECT

    Prevent deletion of the referenced object by raising ProtectedError, a subclass of django.db.IntegrityError.

  • SET_NULL

    Set the ForeignKey null; this is only possible if null is True.

  • SET_DEFAULT

    Set the ForeignKey to its default value; a default for the ForeignKey must be set.

  • SET()

    Set the ForeignKey to the value passed to SET(), or if a callable is passed in, the result of calling it. In most cases, passing a callable will be necessary to avoid executing queries at the time your models.py is imported:

    Code
    from django.conf import settings
from django.contrib.auth import get_user_model
from django.db import models

def get_sentinel_user():
    return get_user_model().objects.get_or_create(username='deleted')[0]

class MyModel(models.Model):
    user = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.SET(get_sentinel_user),
    )
  • DO_NOTHING

    Take no action. If your database backend enforces referential integrity, this will cause an IntegrityError unless you manually add an SQL ON DELETE constraint to the database field.

ForeignKey.limit_choices_to

Sets a limit to the available choices for this field when this field is rendered using a ModelForm or the admin (by default, all objects in the queryset are available to choose). Either a dictionary, a Q object, or a callable returning a dictionary or Q object can be used.

例:

Code
staff_member = models.ForeignKey(
    User,
    on_delete=models.CASCADE,
    limit_choices_to={'is_staff': True},
)

causes the corresponding field on the ModelForm to list only Users that have is_staff=True. This may be helpful in the Django admin.

The callable form can be helpful, for instance, when used in conjunction with the Python datetime module to limit selections by date range. For example:

Code
def limit_pub_date_choices():
    return {'pub_date__lte': datetime.date.utcnow()}

limit_choices_to = limit_pub_date_choices

If limit_choices_to is or returns a Q object, which is useful for complex queries, then it will only have an effect on the choices available in the admin when the field is not listed in raw_id_fields in the ModelAdmin for the model.

ForeignKey.related_name

The name to use for the relation from the related object back to this one. It's also the default value for related_query_name (the name to use for the reverse filter name from the target model). See the related objects documentation for a full explanation and example. Note that you must set this value when defining relations on abstract models; and when you do so some special syntax is available.

If you'd prefer Django not to create a backwards relation, set related_name to '+' or end it with '+'. For example, this will ensure that the User model won't have a backwards relation to this model:

Code
user = models.ForeignKey(
    User,
    on_delete=models.CASCADE,
    related_name='+',
)
ForeignKey.related_query_name

The name to use for the reverse filter name from the target model. It defaults to the value of related_name or default_related_name if set, otherwise it defaults to the name of the model:

Code
# Declare the ForeignKey with related_query_name
class Tag(models.Model):
    article = models.ForeignKey(
        Article,
        on_delete=models.CASCADE,
        related_name="tags",
        related_query_name="tag",
    )
    name = models.CharField(max_length=255)

# That's now the name of the reverse filter
Article.objects.filter(tag__name="important")

Like related_name, related_query_name supports app label and class interpolation via some special syntax.

ForeignKey.to_field

The field on the related object that the relation is to. By default, Django uses the primary key of the related object. If you reference a different field, that field must have unique=True.

ForeignKey.db_constraint

Controls whether or not a constraint should be created in the database for this foreign key. The default is True, and that's almost certainly what you want; setting this to False can be very bad for data integrity. That said, here are some scenarios where you might want to do this:

  • You have legacy data that is not valid.

  • You're sharding your database.

If this is set to False, accessing a related object that doesn't exist will raise its DoesNotExist exception.

ForeignKey.swappable

Controls the migration framework's reaction if this ForeignKey is pointing at a swappable model. If it is True - the default - then if the ForeignKey is pointing at a model which matches the current value of settings.AUTH_USER_MODEL (or another swappable model setting) the relationship will be stored in the migration using a reference to the setting, not to the model directly.

You only want to override this to be False if you are sure your model should always point towards the swapped-in model - for example, if it is a profile model designed specifically for your custom user model.

Setting it to False does not mean you can reference a swappable model even if it is swapped out - False means that the migrations made with this ForeignKey will always reference the exact model you specify (so it will fail hard if the user tries to run with a User model you don't support, for example).

If in doubt, leave it to its default of True.

ManyToManyField

class ManyToManyField(to, **options)

A many-to-many relationship. Requires a positional argument: the class to which the model is related, which works exactly the same as it does for ForeignKey, including recursive and lazy relationships.

Related objects can be added, removed, or created with the field's RelatedManager.

Database Representation

Behind the scenes, Django creates an intermediary join table to represent the many-to-many relationship. By default, this table name is generated using the name of the many-to-many field and the name of the table for the model that contains it. Since some databases don't support table names above a certain length, these table names will be automatically truncated and a uniqueness hash will be used, e.g. author_books_9cdf. You can manually provide the name of the join table using the db_table option.

引数

ManyToManyField accepts an extra set of arguments -- all optional -- that control how the relationship functions.

ManyToManyField.related_name

Same as ForeignKey.related_name.

ManyToManyField.related_query_name

Same as ForeignKey.related_query_name.

ManyToManyField.limit_choices_to

Same as ForeignKey.limit_choices_to.

limit_choices_to has no effect when used on a ManyToManyField with a custom intermediate table specified using the through parameter.

ManyToManyField.symmetrical

Only used in the definition of ManyToManyFields on self. Consider the following model:

Code
from django.db import models

class Person(models.Model):
    friends = models.ManyToManyField("self")

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 many-to-many relationships with self, set symmetrical to False. This will force Django to add the descriptor for the reverse relationship, allowing ManyToManyField relationships to be non-symmetrical.

ManyToManyField.through

Django will automatically generate a table to manage many-to-many relationships. However, if you want to manually specify the intermediary table, you can use the through option to specify the Django model that represents the intermediate table that you want to use.

The most common use for this option is when you want to associate extra data with a many-to-many relationship.

If you don't specify an explicit through model, there is still an implicit through model class you can use to directly access the table created to hold the association. It has three fields to link the models.

If the source and target models differ, the following fields are generated:

  • id: the primary key of the relation.

  • <containing_model>_id: the id of the model that declares the ManyToManyField.

  • <other_model>_id: the id of the model that the ManyToManyField points to.

If the ManyToManyField points from and to the same model, the following fields are generated:

  • id: the primary key of the relation.

  • from_<model>_id: the id of the instance which points at the model (i.e. the source instance).

  • to_<model>_id: the id of the instance to which the relationship points (i.e. the target model instance).

This class can be used to query associated records for a given model instance like a normal model:

Code
Model.m2mfield.through.objects.all()
ManyToManyField.through_fields

Only used when a custom intermediary model is specified. Django will normally determine which fields of the intermediary model to use in order to establish a many-to-many relationship automatically. However, consider the following models:

Code
from django.db import models

class Person(models.Model):
    name = models.CharField(max_length=50)

class Group(models.Model):
    name = models.CharField(max_length=128)
    members = models.ManyToManyField(
        Person,
        through='Membership',
        through_fields=('group', 'person'),
    )

class Membership(models.Model):
    group = models.ForeignKey(Group, on_delete=models.CASCADE)
    person = models.ForeignKey(Person, on_delete=models.CASCADE)
    inviter = models.ForeignKey(
        Person,
        on_delete=models.CASCADE,
        related_name="membership_invites",
    )
    invite_reason = models.CharField(max_length=64)

Membership has two foreign keys to Person (person and inviter), which makes the relationship ambiguous and Django can't know which one to use. In this case, you must explicitly specify which foreign keys Django should use using through_fields, as in the example above.

through_fields accepts a 2-tuple ('field1', 'field2'), where field1 is the name of the foreign key to the model the ManyToManyField is defined on (group in this case), and field2 the name of the foreign key to the target model (person in this case).

When you have more than one foreign key on an intermediary model to any (or even both) of the models participating in a many-to-many relationship, you must specify through_fields. This also applies to recursive relationships when an intermediary model is used and there are more than two foreign keys to the model, or you want to explicitly specify which two Django should use.

ManyToManyField.db_table

The name of the table to create for storing the many-to-many data. If this is not provided, Django will assume a default name based upon the names of: the table for the model defining the relationship and the name of the field itself.

ManyToManyField.db_constraint

Controls whether or not constraints should be created in the database for the foreign keys in the intermediary table. The default is True, and that's almost certainly what you want; setting this to False can be very bad for data integrity. That said, here are some scenarios where you might want to do this:

  • You have legacy data that is not valid.

  • You're sharding your database.

It is an error to pass both db_constraint and through.

ManyToManyField.swappable

Controls the migration framework's reaction if this ManyToManyField is pointing at a swappable model. If it is True - the default - then if the ManyToManyField is pointing at a model which matches the current value of settings.AUTH_USER_MODEL (or another swappable model setting) the relationship will be stored in the migration using a reference to the setting, not to the model directly.

You only want to override this to be False if you are sure your model should always point towards the swapped-in model - for example, if it is a profile model designed specifically for your custom user model.

If in doubt, leave it to its default of True.

ManyToManyField does not support validators.

null has no effect since there is no way to require a relationship at the database level.

OneToOneField

class OneToOneField(to, on_delete, parent_link=False, **options)

A one-to-one relationship. Conceptually, this is similar to a ForeignKey with unique=True, but the "reverse" side of the relation will directly return a single object.

This is most useful as the primary key of a model which "extends" another model in some way; 複数テーブルの継承 is implemented by adding an implicit one-to-one relation from the child model to the parent model, for example.

One positional argument is required: the class to which the model will be related. This works exactly the same as it does for ForeignKey, including all the options regarding recursive and lazy relationships.

If you do not specify the related_name argument for the OneToOneField, Django will use the lowercase name of the current model as default value.

With the following example:

Code
from django.conf import settings
from django.db import models

class MySpecialUser(models.Model):
    user = models.OneToOneField(
        settings.AUTH_USER_MODEL,
        on_delete=models.CASCADE,
    )
    supervisor = models.OneToOneField(
        settings.AUTH_USER_MODEL,
        on_delete=models.CASCADE,
        related_name='supervisor_of',
    )

your resulting User model will have the following attributes:

Code
>>> user = User.objects.get(pk=1)
>>> hasattr(user, 'myspecialuser')
True
>>> hasattr(user, 'supervisor_of')
True

A RelatedObjectDoesNotExist exception is raised when accessing the reverse relationship if an entry in the related table doesn't exist. This is a subclass of the target model's Model.DoesNotExist exception. For example, if a user doesn't have a supervisor designated by MySpecialUser:

Code
>>> user.supervisor_of
Traceback (most recent call last):
    ...
RelatedObjectDoesNotExist: User has no supervisor_of.

Additionally, OneToOneField accepts all of the extra arguments accepted by ForeignKey, plus one extra argument:

When True and used in a model which inherits from another concrete model, indicates that this field should be used as the link back to the parent class, rather than the extra OneToOneField which would normally be implicitly created by subclassing.

See One-to-one relationships for usage examples of OneToOneField.

Field API reference

class Field

Field is an abstract class that represents a database table column. Django uses fields to create the database table (db_type()), to map Python types to database (get_prep_value()) and vice-versa (from_db_value()).

A field is thus a fundamental piece in different Django APIs, notably, models and querysets.

In models, a field is instantiated as a class attribute and represents a particular table column, see モデル. It has attributes such as null and unique, and methods that Django uses to map the field value to database-specific values.

A Field is a subclass of RegisterLookupMixin and thus both Transform and Lookup can be registered on it to be used in QuerySets (e.g. field_name__exact="foo"). All built-in lookups are registered by default.

All of Django's built-in fields, such as CharField, are particular implementations of Field. If you need a custom field, you can either subclass any of the built-in fields or write a Field from scratch. In either case, see カスタム model fieldsの実装.

description

A verbose description of the field, e.g. for the django.contrib.admindocs application.

The description can be of the form:

Code
description = _("String (up to %(max_length)s)")

where the arguments are interpolated from the field's __dict__.

descriptor_class

A class implementing the descriptor protocol that is instantiated and assigned to the model instance attribute. The constructor must accept a single argument, the Field instance. Overriding this class attribute allows for customizing the get and set behavior.

To map a Field to a database-specific type, Django exposes several methods:

get_internal_type()

Returns a string naming this field for backend specific purposes. By default, it returns the class name.

See Emulating built-in field types for usage in custom fields.

db_type(connection)

Returns the database column data type for the Field, taking into account the connection.

See カスタムデータベースタイプ for usage in custom fields.

rel_db_type(connection)

Returns the database column data type for fields such as ForeignKey and OneToOneField that point to the Field, taking into account the connection.

See カスタムデータベースタイプ for usage in custom fields.

There are three main situations where Django needs to interact with the database backend and fields:

  • when it queries the database (Python value -> database backend value)

  • when it loads data from the database (database backend value -> Python value)

  • when it saves to the database (Python value -> database backend value)

When querying, get_db_prep_value() and get_prep_value() are used:

get_prep_value(value)

value is the current value of the model's attribute, and the method should return data in a format that has been prepared for use as a parameter in a query.

See Converting Python objects to query values for usage.

get_db_prep_value(value, connection, prepared=False)

Converts value to a backend-specific value. By default it returns value if prepared=True and get_prep_value() if is False.

See Converting query values to database values for usage.

When loading data, from_db_value() is used:

from_db_value(value, expression, connection)

Converts a value as returned by the database to a Python object. It is the reverse of get_prep_value().

This method is not used for most built-in fields as the database backend already returns the correct Python type, or the backend itself does the conversion.

expression is the same as self.

See Converting values to Python objects for usage.

When saving, pre_save() and get_db_prep_save() are used:

get_db_prep_save(value, connection)

Same as the get_db_prep_value(), but called when the field value must be saved to the database. By default returns get_db_prep_value().

pre_save(model_instance, add)

Method called prior to get_db_prep_save() to prepare the value before being saved (e.g. for DateField.auto_now).

model_instance is the instance this field belongs to and add is whether the instance is being saved to the database for the first time.

It should return the value of the appropriate attribute from model_instance for this field. The attribute name is in self.attname (this is set up by Field).

See Preprocessing values before saving for usage.

Fields often receive their values as a different type, either from serialization or from forms.

to_python(value)

Converts the value into the correct Python object. It acts as the reverse of value_to_string(), and is also called in clean().

See Converting values to Python objects for usage.

Besides saving to the database, the field also needs to know how to serialize its value:

value_from_object(obj)

Returns the field's value for the given model instance.

This method is often used by value_to_string().

value_to_string(obj)

Converts obj to a string. Used to serialize the value of the field.

See Converting field data for serialization for usage.

When using model forms, the Field needs to know which form field it should be represented by:

formfield(form_class=None, choices_form_class=None, **kwargs)

Returns the default django.forms.Field of this field for ModelForm.

By default, if both form_class and choices_form_class are None, it uses CharField. If the field has choices and choices_form_class isn't specified, it uses TypedChoiceField.

See Specifying the form field for a model field for usage.

deconstruct()

Returns a 4-tuple with enough information to recreate the field:

  1. The name of the field on the model.

  2. The import path of the field (e.g. "django.db.models.IntegerField"). This should be the most portable version, so less specific may be better.

  3. A list of positional arguments.

  4. A dict of keyword arguments.

This method must be added to fields prior to 1.7 to migrate its data using マイグレーション.

Field attribute reference

Every Field instance contains several attributes that allow introspecting its behavior. Use these attributes instead of isinstance checks when you need to write code that depends on a field's functionality. These attributes can be used together with the Model._meta API to narrow down a search for specific field types. Custom model fields should implement these flags.

Attributes for fields

Field.auto_created

Boolean flag that indicates if the field was automatically created, such as the OneToOneField used by model inheritance.

Field.concrete

Boolean flag that indicates if the field has a database column associated with it.

Field.hidden

Boolean flag that indicates if a field is used to back another non-hidden field's functionality (e.g. the content_type and object_id fields that make up a GenericForeignKey). The hidden flag is used to distinguish what constitutes the public subset of fields on the model from all the fields on the model.

Field.is_relation

Boolean flag that indicates if a field contains references to one or more other models for its functionality (e.g. ForeignKey, ManyToManyField, OneToOneField, etc.).

Field.model

Returns the model on which the field is defined. If a field is defined on a superclass of a model, model will refer to the superclass, not the class of the instance.

Attributes for fields with relations

These attributes are used to query for the cardinality and other details of a relation. These attribute are present on all fields; however, they will only have boolean values (rather than None) if the field is a relation type (Field.is_relation=True).

Field.many_to_many

Boolean flag that is True if the field has a many-to-many relation; False otherwise. The only field included with Django where this is True is ManyToManyField.

Field.many_to_one

Boolean flag that is True if the field has a many-to-one relation, such as a ForeignKey; False otherwise.

Field.one_to_many

Boolean flag that is True if the field has a one-to-many relation, such as a GenericRelation or the reverse of a ForeignKey; False otherwise.

Field.one_to_one

Boolean flag that is True if the field has a one-to-one relation, such as a OneToOneField; False otherwise.

Field.related_model

Points to the model the field relates to. For example, Author in ForeignKey(Author, on_delete=models.CASCADE). The related_model for a GenericForeignKey is always None.

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