本文档包含 Field 类的所有 API 参考，包括 field options 和 field types。
以下参数对所以字段类型均有效，且是可选的。
\nnullLink to this heading#如果设置为 True， 当该字段为空时，Django 会将数据库中该字段设置为 NULL，默认为 False。
避免在基于字符串的字段（例如 CharField 和 TextField）上使用 null。如果字符串字段的 null=True，那意味着对于“无数据”有两个可能的值：NULL 和空字符串。在大多数情况下，对于“无数据”声明两个值是赘余的，Django 的惯例是使用空字符串而不是 NULL。 一个例外是当 CharField 同时具有 unique=True 和 blank=True 时。 在这种情况下，需要设置 null=True，以便在使用空白值保存多个对象时避免唯一的约束违规。
For both string-based and non-string-based fields, you will also need to\nset blank=True if you wish to permit empty values in forms, as the\nnull parameter only affects database storage\n(see blank).
blankLink to this heading#如果设置为 True ，该字段允许为空。默认为 False 。
Note that this is different than null. null is\npurely database-related, whereas blank is validation-related. If\na field has blank=True, form validation will allow entry of an empty value.\nIf a field has blank=False, the field will be required.
choicesLink to this heading#A sequence consisting itself of iterables of exactly two items (e.g.\n[(A, B), (A, B) ...]) to use as choices for this field. If choices are\ngiven, they're enforced by model validation and the\ndefault form widget will be a select box with these choices instead of the\nstandard text field.
The first element in each tuple is the actual value to be set on the model,\nand the second element is the human-readable name. For example:
\nYEAR_IN_SCHOOL_CHOICES = [\n ('FR', 'Freshman'),\n ('SO', 'Sophomore'),\n ('JR', 'Junior'),\n ('SR', 'Senior'),\n]\nGenerally, it's best to define choices inside a model class, and to\ndefine a suitably-named constant for each value:
\nfrom django.db import models\n\nclass Student(models.Model):\n FRESHMAN = 'FR'\n SOPHOMORE = 'SO'\n JUNIOR = 'JR'\n SENIOR = 'SR'\n YEAR_IN_SCHOOL_CHOICES = [\n (FRESHMAN, 'Freshman'),\n (SOPHOMORE, 'Sophomore'),\n (JUNIOR, 'Junior'),\n (SENIOR, 'Senior'),\n ]\n year_in_school = models.CharField(\n max_length=2,\n choices=YEAR_IN_SCHOOL_CHOICES,\n default=FRESHMAN,\n )\n\n def is_upperclass(self):\n return self.year_in_school in (self.JUNIOR, self.SENIOR)\nThough you can define a choices list outside of a model class and then\nrefer to it, defining the choices and names for each choice inside the\nmodel class keeps all of that information with the class that uses it,\nand makes the choices easy to reference (e.g, Student.SOPHOMORE\nwill work anywhere that the Student model has been imported).
You can also collect your available choices into named groups that can\nbe used for organizational purposes:
\nMEDIA_CHOICES = [\n ('Audio', (\n ('vinyl', 'Vinyl'),\n ('cd', 'CD'),\n )\n ),\n ('Video', (\n ('vhs', 'VHS Tape'),\n ('dvd', 'DVD'),\n )\n ),\n ('unknown', 'Unknown'),\n]\nThe first element in each tuple is the name to apply to the group. The\nsecond element is an iterable of 2-tuples, with each 2-tuple containing\na value and a human-readable name for an option. Grouped options may be\ncombined with ungrouped options within a single list (such as the\nunknown option in this example).
\nFor each model field that has choices set, Django will add a\nmethod to retrieve the human-readable name for the field's current value. See\nget_FOO_display() in the database API\ndocumentation.
Note that choices can be any sequence object -- not necessarily a list or\ntuple. This lets you construct choices dynamically. But if you find yourself\nhacking choices to be dynamic, you're probably better off using\na proper database table with a ForeignKey. choices is\nmeant for static data that doesn't change much, if ever.
Unless blank=False is set on the field along with a\ndefault then a label containing "---------" will be rendered\nwith the select box. To override this behavior, add a tuple to choices\ncontaining None; e.g. (None, 'Your String For Display').\nAlternatively, you can use an empty string instead of None where this makes\nsense - such as on a CharField.
db_columnLink to this heading#The name of the database column to use for this field. If this isn't given,\nDjango will use the field's name.
\nIf your database column name is an SQL reserved word, or contains\ncharacters that aren't allowed in Python variable names -- notably, the\nhyphen -- that's OK. Django quotes column and table names behind the\nscenes.
\ndb_indexLink to this heading#If True, a database index will be created for this field.
db_tablespaceLink to this heading#The name of the database tablespace to use for\nthis field's index, if this field is indexed. The default is the project's\nDEFAULT_INDEX_TABLESPACE setting, if set, or the\ndb_tablespace of the model, if any. If the backend doesn't\nsupport tablespaces for indexes, this option is ignored.
defaultLink to this heading#该字段的默认值。可以是一个值或者是个可调用的对象，如果是个可调用对象，每次实例化模型时都会调用该对象。
\nThe default can't be a mutable object (model instance, list, set, etc.),\nas a reference to the same instance of that object would be used as the default\nvalue in all new model instances. Instead, wrap the desired default in a\ncallable. For example, if you want to specify a default dict for\nJSONField, use a function:
def contact_default():\n return {"email": "to1@example.com"}\n\ncontact_info = JSONField("ContactInfo", default=contact_default)\nlambdas can't be used for field options like default because they\ncan't be serialized by migrations. See that\ndocumentation for other caveats.
For fields like ForeignKey that map to model instances, defaults\nshould be the value of the field they reference (pk unless\nto_field is set) instead of model instances.
The default value is used when new model instances are created and a value\nisn't provided for the field. When the field is a primary key, the default is\nalso used when the field is set to None.
editableLink to this heading#If False, the field will not be displayed in the admin or any other\nModelForm. They are also skipped during model\nvalidation. Default is True.
error_messagesLink to this heading#The error_messages argument lets you override the default messages that the\nfield will raise. Pass in a dictionary with keys matching the error messages you\nwant to override.
Error message keys include null, blank, invalid, invalid_choice,\nunique, and unique_for_date. Additional error message keys are\nspecified for each field in the Field types section below.
These error messages often don't propagate to forms. See\n有关模型的 error_messages 的注意事项.
\nhelp_textLink to this heading#额外的“帮助”文本，随表单控件一同显示。即便你的字段未用于表单，它对于生成文档也是很有用的。
\nNote that this value is not HTML-escaped in automatically-generated\nforms. This lets you include HTML in help_text if you so\ndesire. For example:
help_text="Please use the following format: <em>YYYY-MM-DD</em>."\nAlternatively you can use plain text and\ndjango.utils.html.escape() to escape any HTML special characters. Ensure\nthat you escape any help text that may come from untrusted users to avoid a\ncross-site scripting attack.
primary_keyLink to this heading#如果设置为 True ，将该字段设置为该模型的主键。
If you don't specify primary_key=True for any field in your model, Django\nwill automatically add an AutoField to hold the primary key, so you\ndon't need to set primary_key=True on any of your fields unless you want to\noverride the default primary-key behavior. For more, see\n自动设置主键.
primary_key=True implies null=False and\nunique=True. Only one primary key is allowed on an\nobject.
The primary key field is read-only. If you change the value of the primary\nkey on an existing object and then save it, a new object will be created\nalongside the old one.
\nuniqueLink to this heading#如果设置为 True，这个字段必须在整个表中保持值唯一。
This is enforced at the database level and by model validation. If\nyou try to save a model with a duplicate value in a unique\nfield, a django.db.IntegrityError will be raised by the model's\nsave() method.
This option is valid on all field types except ManyToManyField and\nOneToOneField.
Note that when unique is True, you don't need to specify\ndb_index, because unique implies the creation of an index.
unique_for_dateLink to this heading#Set this to the name of a DateField or DateTimeField to\nrequire that this field be unique for the value of the date field.
For example, if you have a field title that has\nunique_for_date="pub_date", then Django wouldn't allow the entry of two\nrecords with the same title and pub_date.
Note that if you set this to point to a DateTimeField, only the date\nportion of the field will be considered. Besides, when USE_TZ is\nTrue, 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\nbut not at the database level. If any unique_for_date constraint\ninvolves fields that are not part of a ModelForm (for\nexample, if one of the fields is listed in exclude or has\neditable=False), Model.validate_unique() will\nskip validation for that particular constraint.
unique_for_monthLink to this heading#Like unique_for_date, but requires the field to be unique with\nrespect to the month.
unique_for_yearLink to this heading#Like unique_for_date and unique_for_month.
verbose_nameLink to this heading#A human-readable name for the field. If the verbose name isn't given, Django\nwill automatically create it using the field's attribute name, converting\nunderscores to spaces. See Verbose field names.
\nvalidatorsLink to this heading#A list of validators to run for this field. See the validators\ndocumentation for more information.
\nField implements the lookup registration API.\nThe API can be used to customize which lookups are available for a field class, and\nhow lookups are fetched from a field.
AutoFieldLink to this heading#An IntegerField that automatically increments\naccording to available IDs. You usually won't need to use this directly; a\nprimary key field will automatically be added to your model if you don't specify\notherwise. See 自动设置主键.
BigAutoFieldLink to this heading#A 64-bit integer, much like an AutoField except that it is\nguaranteed to fit numbers from 1 to 9223372036854775807.
BigIntegerFieldLink to this heading#A 64-bit integer, much like an IntegerField except that it is\nguaranteed to fit numbers from -9223372036854775808 to\n9223372036854775807. The default form widget for this field is a\nTextInput.
BinaryFieldLink to this heading#A field to store raw binary data. It can be assigned bytes,\nbytearray, or memoryview.
By default, BinaryField sets editable to False, in which\ncase it can't be included in a ModelForm.
BinaryField has one extra optional argument:
The maximum length (in characters) of the field. The maximum length is\nenforced in Django's validation using\nMaxLengthValidator.
BooleanFieldLink to this heading#A true/false field.
\nThe default form widget for this field is CheckboxInput,\nor NullBooleanSelect if null=True.
The default value of BooleanField is None when Field.default\nisn't defined.
CharFieldLink to this heading#A string field, for small- to large-sized strings.
\nFor large amounts of text, use TextField.
The default form widget for this field is a TextInput.
CharField has one extra required argument:
The maximum length (in characters) of the field. The max_length is enforced\nat the database level and in Django's validation using\nMaxLengthValidator.
DateFieldLink to this heading#A date, represented in Python by a datetime.date instance. Has a few extra,\noptional arguments:
Automatically set the field to now every time the object is saved. Useful\nfor "last-modified" timestamps. Note that the current date is always\nused; it's not just a default value that you can override.
\nThe field is only automatically updated when calling Model.save(). The field isn't updated when making updates\nto other fields in other ways such as QuerySet.update(), though you can specify a custom\nvalue for the field in an update like that.
Automatically set the field to now when the object is first created. Useful\nfor creation of timestamps. Note that the current date is always used;\nit's not just a default value that you can override. So even if you\nset a value for this field when creating the object, it will be ignored.\nIf you want to be able to modify this field, set the following instead of\nauto_now_add=True:
For DateField: default=date.today - from\ndatetime.date.today()
For DateTimeField: default=timezone.now - from\ndjango.utils.timezone.now()
The default form widget for this field is a\nTextInput. The admin adds a JavaScript calendar,\nand a shortcut for "Today". Includes an additional invalid_date error\nmessage key.
The options auto_now_add, auto_now, and default are mutually exclusive.\nAny combination of these options will result in an error.
DateTimeFieldLink to this heading#A date and time, represented in Python by a datetime.datetime instance.\nTakes the same extra arguments as DateField.
The default form widget for this field is a single\nTextInput. The admin uses two separate\nTextInput widgets with JavaScript shortcuts.
DecimalFieldLink to this heading#A fixed-precision decimal number, represented in Python by a\nDecimal instance. It validates the input using\nDecimalValidator.
Has two required arguments:
\nThe maximum number of digits allowed in the number. Note that this number\nmust be greater than or equal to decimal_places.
The number of decimal places to store with the number.
\nFor example, to store numbers up to 999 with a resolution of 2 decimal\nplaces, you'd use:
models.DecimalField(..., max_digits=5, decimal_places=2)\nAnd to store numbers up to approximately one billion with a resolution of 10\ndecimal places:
\nmodels.DecimalField(..., max_digits=19, decimal_places=10)\nThe default form widget for this field is a NumberInput\nwhen localize is False or\nTextInput otherwise.
DurationFieldLink to this heading#A field for storing periods of time - modeled in Python by\ntimedelta. When used on PostgreSQL, the data type\nused is an interval and on Oracle the data type is INTERVAL DAY(9) TO\nSECOND(6). Otherwise a bigint of microseconds is used.
EmailFieldLink to this heading#A CharField that checks that the value is a valid email address using\nEmailValidator.
FileFieldLink to this heading#A file-upload field.
\n\nHas two optional arguments:
\nThis attribute provides a way of setting the upload directory and file name,\nand can be set in two ways. In both cases, the value is passed to the\nStorage.save() method.
If you specify a string value, it may contain strftime()\nformatting, which will be replaced by the date/time of the file upload (so\nthat uploaded files don't fill up the given directory). For example:
class MyModel(models.Model):\n # file will be uploaded to MEDIA_ROOT/uploads\n upload = models.FileField(upload_to='uploads/')\n # or...\n # file will be saved to MEDIA_ROOT/uploads/2015/01/30\n upload = models.FileField(upload_to='uploads/%Y/%m/%d/')\nIf you are using the default\nFileSystemStorage, the string value\nwill be appended to your MEDIA_ROOT path to form the location on\nthe local filesystem where uploaded files will be stored. If you are using\na different storage, check that storage's documentation to see how it\nhandles upload_to.
upload_to may also be a callable, such as a function. This will be\ncalled to obtain the upload path, including the filename. This callable must\naccept two arguments and return a Unix-style path (with forward slashes)\nto be passed along to the storage system. The two arguments are:
Argument | \n描述 | \n
|---|---|
| \nAn instance of the model where the\n In most cases, this object will not have been\nsaved to the database yet, so if it uses the\ndefault | \n
| \nThe filename that was originally given to the\nfile. This may or may not be taken into account\nwhen determining the final destination path. | \n
例子:
\ndef user_directory_path(instance, filename):\n # file will be uploaded to MEDIA_ROOT/user_<id>/<filename>\n return 'user_{0}/{1}'.format(instance.user.id, filename)\n\nclass MyModel(models.Model):\n upload = models.FileField(upload_to=user_directory_path)\nA storage object, which handles the storage and retrieval of your\nfiles. See 管理文件 for details on how to provide this object.
\nThe default form widget for this field is a\nClearableFileInput.
Using a FileField or an ImageField (see below) in a model\ntakes a few steps:
在你的 setting 文件中，你需要定义：setting: MEDIA_ROOT 作为 Django 存储上传文件目录的完整路径。（为了提高性能，这些文件不会储存在数据库中）定义： setting: MEDIA_URL 作为该目录的基本公共 URL， 确保该目录能够被 Web 服务器的是用户写入。
Add the FileField or ImageField to your model, defining\nthe upload_to option to specify a subdirectory of\nMEDIA_ROOT to use for uploaded files.
All that will be stored in your database is a path to the file\n(relative to MEDIA_ROOT). You'll most likely want to use the\nconvenience url attribute\nprovided by Django. For example, if your ImageField is called\nmug_shot, you can get the absolute path to your image in a template with\n{{ object.mug_shot.url }}.
For example, say your MEDIA_ROOT is set to '/home/media', and\nupload_to is set to 'photos/%Y/%m/%d'. The '%Y/%m/%d'\npart of upload_to is strftime() formatting;\n'%Y' is the four-digit year, '%m' is the two-digit month and '%d' is\nthe two-digit day. If you upload a file on Jan. 15, 2007, it will be saved in\nthe directory /home/media/photos/2007/01/15.
If you wanted to retrieve the uploaded file's on-disk filename, or the file's\nsize, you could use the name and\nsize attributes respectively; for more\ninformation on the available attributes and methods, see the\nFile class reference and the 管理文件\ntopic guide.
The uploaded file's relative URL can be obtained using the\nurl attribute. Internally,\nthis calls the url() method of the\nunderlying Storage class.
Note that whenever you deal with uploaded files, you should pay close attention\nto where you're uploading them and what type of files they are, to avoid\nsecurity holes. Validate all uploaded files so that you're sure the files are\nwhat you think they are. For example, if you blindly let somebody upload files,\nwithout validation, to a directory that's within your Web server's document\nroot, then somebody could upload a CGI or PHP script and execute that script by\nvisiting its URL on your site. Don't allow that.
\nAlso note that even an uploaded HTML file, since it can be executed by the\nbrowser (though not by the server), can pose security threats that are\nequivalent to XSS or CSRF attacks.
\nFileField instances are created in your database as varchar\ncolumns with a default max length of 100 characters. As with other fields, you\ncan change the maximum length using the max_length argument.
FileField``和``FieldFileLink to this heading#When you access a FileField on a model, you are\ngiven an instance of FieldFile as a proxy for accessing the underlying\nfile.
The API of FieldFile mirrors that of File,\nwith one key difference: The object wrapped by the class is not necessarily a\nwrapper around Python's built-in file object. Instead, it is a wrapper around\nthe result of the Storage.open()\nmethod, which may be a File object, or it may be a\ncustom storage's implementation of the File API.
In addition to the API inherited from File such as\nread() and write(), FieldFile includes several methods that\ncan be used to interact with the underlying file:
The name of the file including the relative path from the root of the\nStorage of the associated\nFileField.
The result of the underlying Storage.size() method.
A read-only property to access the file's relative URL by calling the\nurl() method of the underlying\nStorage class.
Opens or reopens the file associated with this instance in the specified\nmode. Unlike the standard Python open() method, it doesn't return a\nfile descriptor.
Since the underlying file is opened implicitly when accessing it, it may be\nunnecessary to call this method except to reset the pointer to the underlying\nfile or to change the mode.
Behaves like the standard Python file.close() method and closes the file\nassociated with this instance.
This method takes a filename and file contents and passes them to the storage\nclass for the field, then associates the stored file with the model field.\nIf you want to manually associate file data with\nFileField instances on your model, the save()\nmethod is used to persist that file data.
Takes two required arguments: name which is the name of the file, and\ncontent which is an object containing the file's contents. The\noptional save argument controls whether or not the model instance is\nsaved after the file associated with this field has been altered. Defaults to\nTrue.
Note that the content argument should be an instance of\ndjango.core.files.File, not Python's built-in file object.\nYou can construct a File from an existing\nPython file object like this:
from django.core.files import File\n# Open an existing file using Python's built-in open()\nf = open('/path/to/hello.world')\nmyfile = File(f)\nOr you can construct one from a Python string like this:
\nfrom django.core.files.base import ContentFile\nmyfile = ContentFile("hello world")\nFor more information, see 管理文件.
\nDeletes the file associated with this instance and clears all attributes on\nthe field. Note: This method will close the file if it happens to be open when\ndelete() is called.
The optional save argument controls whether or not the model instance is\nsaved after the file associated with this field has been deleted. Defaults to\nTrue.
Note that when a model is deleted, related files are not deleted. If you need\nto cleanup orphaned files, you'll need to handle it yourself (for instance,\nwith a custom management command that can be run manually or scheduled to run\nperiodically via e.g. cron).
\nFilePathFieldLink to this heading#A CharField whose choices are limited to the filenames in a certain\ndirectory on the filesystem. Has three special arguments, of which the first is\nrequired:
Required. The absolute filesystem path to a directory from which this\nFilePathField should get its choices. Example: "/home/images".
Optional. A regular expression, as a string, that FilePathField\nwill use to filter filenames. Note that the regex will be applied to the\nbase filename, not the full path. Example: "foo.*\\.txt$", which will\nmatch a file called foo23.txt but not bar.txt or foo23.png.
Optional. Either True or False. Default is False. Specifies\nwhether all subdirectories of path should be included
Optional. Either True or False. Default is True. Specifies\nwhether files in the specified location should be included. Either this or\nallow_folders must be True.
Optional. Either True or False. Default is False. Specifies\nwhether folders in the specified location should be included. Either this\nor allow_files must be True.
当然，这些参数能够同时使用。
\nThe one potential gotcha is that match applies to the\nbase filename, not the full path. So, this example:
FilePathField(path="/home/images", match="foo.*", recursive=True)\n...will match /home/images/foo.png but not /home/images/foo/bar.png\nbecause the match applies to the base filename\n(foo.png and bar.png).
FilePathField instances are created in your database as varchar\ncolumns with a default max length of 100 characters. As with other fields, you\ncan change the maximum length using the max_length argument.
FloatFieldLink to this heading#A floating-point number represented in Python by a float instance.
The default form widget for this field is a NumberInput\nwhen localize is False or\nTextInput otherwise.
ImageFieldLink to this heading#Inherits all attributes and methods from FileField, but also\nvalidates that the uploaded object is a valid image.
In addition to the special attributes that are available for FileField,\nan ImageField also has height and width attributes.
To facilitate querying on those attributes, ImageField has two extra\noptional arguments:
Name of a model field which will be auto-populated with the height of the\nimage each time the model instance is saved.
\nName of a model field which will be auto-populated with the width of the\nimage each time the model instance is saved.
\nRequires the Pillow library.
\nImageField instances are created in your database as varchar\ncolumns with a default max length of 100 characters. As with other fields, you\ncan change the maximum length using the max_length argument.
The default form widget for this field is a\nClearableFileInput.
IntegerFieldLink to this heading#An integer. Values from -2147483648 to 2147483647 are safe in all\ndatabases supported by Django.
It uses MinValueValidator and\nMaxValueValidator to validate the input based\non the values that the default database supports.
The default form widget for this field is a NumberInput\nwhen localize is False or\nTextInput otherwise.
GenericIPAddressFieldLink to this heading#An IPv4 or IPv6 address, in string format (e.g. 192.0.2.30 or\n2a02:42fe::4). The default form widget for this field is a\nTextInput.
The IPv6 address normalization follows RFC 4291 Section 2.2 section 2.2,\nincluding using the IPv4 format suggested in paragraph 3 of that section, like\n::ffff:192.0.2.0. For example, 2001:0::0:01 would be normalized to\n2001::1, and ::ffff:0a0a:0a0a to ::ffff:10.10.10.10. All characters\nare converted to lowercase.
Limits valid inputs to the specified protocol.\nAccepted values are 'both' (default), 'IPv4'\nor 'IPv6'. Matching is case insensitive.
Unpacks IPv4 mapped addresses like ::ffff:192.0.2.1.\nIf this option is enabled that address would be unpacked to\n192.0.2.1. Default is disabled. Can only be used\nwhen protocol is set to 'both'.
If you allow for blank values, you have to allow for null values since blank\nvalues are stored as null.
\nNullBooleanFieldLink to this heading#Like BooleanField with null=True. Use that instead of this field\nas it's likely to be deprecated in a future version of Django.
PositiveIntegerFieldLink to this heading#Like an IntegerField, but must be either positive or zero (0).\nValues from 0 to 2147483647 are safe in all databases supported by\nDjango. The value 0 is accepted for backward compatibility reasons.
PositiveSmallIntegerFieldLink to this heading#Like a PositiveIntegerField, but only allows values under a certain\n(database-dependent) point. Values from 0 to 32767 are safe in all\ndatabases supported by Django.
SlugFieldLink to this heading#Slug is a newspaper term. A slug is a short label for something,\ncontaining only letters, numbers, underscores or hyphens. They're generally used\nin URLs.
\nLike a CharField, you can specify max_length (read the note\nabout database portability and max_length in that section,\ntoo). If max_length is not specified, Django will use a\ndefault length of 50.
Implies setting Field.db_index to True.
It is often useful to automatically prepopulate a SlugField based on the value\nof some other value. You can do this automatically in the admin using\nprepopulated_fields.
It uses validate_slug or\nvalidate_unicode_slug for validation.
If True, the field accepts Unicode letters in addition to ASCII\nletters. Defaults to False.
SmallIntegerFieldLink to this heading#Like an IntegerField, but only allows values under a certain\n(database-dependent) point. Values from -32768 to 32767 are safe in all\ndatabases supported by Django.
TextFieldLink to this heading#A large text field. The default form widget for this field is a\nTextarea.
If you specify a max_length attribute, it will be reflected in the\nTextarea widget of the auto-generated form field.\nHowever it is not enforced at the model or database level. Use a\nCharField for that.
TimeFieldLink to this heading#A time, represented in Python by a datetime.time instance. Accepts the same\nauto-population options as DateField.
The default form widget for this field is a TextInput.\nThe admin adds some JavaScript shortcuts.
URLFieldLink to this heading#A CharField for a URL, validated by\nURLValidator.
The default form widget for this field is a TextInput.
Like all CharField subclasses, URLField takes the optional\nmax_length argument. If you don't specify\nmax_length, a default of 200 is used.
UUIDFieldLink to this heading#A field for storing universally unique identifiers. Uses Python's\nUUID class. When used on PostgreSQL, this stores in a\nuuid datatype, otherwise in a char(32).
Universally unique identifiers are a good alternative to AutoField for\nprimary_key. The database will not generate the UUID for you, so\nit is recommended to use default:
import uuid\nfrom django.db import models\n\nclass MyUUIDModel(models.Model):\n id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)\n # other fields\nNote that a callable (with the parentheses omitted) is passed to default,\nnot an instance of UUID.
Field is an abstract class that represents a database table column.\nDjango uses fields to create the database table (db_type()), to map\nPython types to database (get_prep_value()) and vice-versa\n(from_db_value()).
A field is thus a fundamental piece in different Django APIs, notably,\nmodels and querysets.
In models, a field is instantiated as a class attribute and represents a\nparticular table column, see 模型. It has attributes\nsuch as null and unique, and methods that Django uses to\nmap the field value to database-specific values.
A Field is a subclass of\nRegisterLookupMixin and thus both\nTransform and\nLookup can be registered on it to be used\nin QuerySets (e.g. field_name__exact="foo"). All built-in\nlookups are registered by default.
All of Django's built-in fields, such as CharField, are particular\nimplementations of Field. If you need a custom field, you can either\nsubclass any of the built-in fields or write a Field from scratch. In\neither case, see 编写自定义模型字段(model fields).
A verbose description of the field, e.g. for the\ndjango.contrib.admindocs application.
The description can be of the form:
\ndescription = _("String (up to %(max_length)s)")\nwhere the arguments are interpolated from the field's __dict__.
To map a Field to a database-specific type, Django exposes several\nmethods:
Returns a string naming this field for backend specific purposes.\nBy default, it returns the class name.
\nSee 仿造内置字段类型 for usage in custom fields.
\nReturns the database column data type for the Field, taking\ninto account the connection.
See 自定义数据库类型 for usage in custom fields.
\nReturns the database column data type for fields such as ForeignKey\nand OneToOneField that point to the Field, taking\ninto account the connection.
See 自定义数据库类型 for usage in custom fields.
\nThere are three main situations where Django needs to interact with the\ndatabase backend and fields:
\nwhen it queries the database (Python value -> database backend value)
when it loads data from the database (database backend value -> Python\nvalue)
when it saves to the database (Python value -> database backend value)
When querying, get_db_prep_value() and get_prep_value() are used:
value is the current value of the model's attribute, and the method\nshould return data in a format that has been prepared for use as a\nparameter in a query.
See 将 Python 转为查询值 for usage.
\nConverts value to a backend-specific value. By default it returns\nvalue if prepared=True and get_prep_value() if is\nFalse.
See 将查询值转为数据库值 for usage.
\nWhen loading data, from_db_value() is used:
Converts a value as returned by the database to a Python object. It is\nthe reverse of get_prep_value().
This method is not used for most built-in fields as the database\nbackend already returns the correct Python type, or the backend itself\ndoes the conversion.
\nSee 将值转为 Python 对象 for usage.
\n\nWhen saving, pre_save() and get_db_prep_save() are used:
Same as the get_db_prep_value(), but called when the field value\nmust be saved to the database. By default returns\nget_db_prep_value().
Method called prior to get_db_prep_save() to prepare the value\nbefore being saved (e.g. for DateField.auto_now).
model_instance is the instance this field belongs to and add\nis whether the instance is being saved to the database for the first\ntime.
It should return the value of the appropriate attribute from\nmodel_instance for this field. The attribute name is in\nself.attname (this is set up by Field).
See 在保存前预处理数值 for usage.
\nFields often receive their values as a different type, either from\nserialization or from forms.
\nConverts the value into the correct Python object. It acts as the\nreverse of value_to_string(), and is also called in\nclean().
See 将值转为 Python 对象 for usage.
\nBesides saving to the database, the field also needs to know how to\nserialize its value:
\nReturns the field's value for the given model instance.
\nThis method is often used by value_to_string().
Converts obj to a string. Used to serialize the value of the field.
See 为序列化转换字段数据 for usage.
\nWhen using model forms, the Field\nneeds to know which form field it should be represented by:
Returns the default django.forms.Field of this field for\nModelForm.
By default, if both form_class and choices_form_class are\nNone, it uses CharField. If the field has\nchoices and choices_form_class\nisn't specified, it uses TypedChoiceField.
See 为模型字段指定表单字段 for usage.
\nReturns a 4-tuple with enough information to recreate the field:
\nThe name of the field on the model.
The import path of the field (e.g. "django.db.models.IntegerField").\nThis should be the most portable version, so less specific may be better.
A list of positional arguments.
A dict of keyword arguments.
This method must be added to fields prior to 1.7 to migrate its data\nusing 迁移.
\nEvery Field instance contains several attributes that allow\nintrospecting its behavior. Use these attributes instead of isinstance\nchecks when you need to write code that depends on a field's functionality.\nThese attributes can be used together with the Model._meta API to narrow down a search for specific field types.\nCustom model fields should implement these flags.
Boolean flag that indicates if the field was automatically created, such\nas the OneToOneField used by model inheritance.
Boolean flag that indicates if the field has a database column associated\nwith it.
\nBoolean flag that indicates if a field is used to back another non-hidden\nfield's functionality (e.g. the content_type and object_id fields\nthat make up a GenericForeignKey). The hidden flag is used to\ndistinguish what constitutes the public subset of fields on the model from\nall the fields on the model.
Boolean flag that indicates if a field contains references to one or\nmore other models for its functionality (e.g. ForeignKey,\nManyToManyField, OneToOneField, etc.).
Returns the model on which the field is defined. If a field is defined on\na superclass of a model, model will refer to the superclass, not the\nclass of the instance.
These attributes are used to query for the cardinality and other details of a\nrelation. These attribute are present on all fields; however, they will only\nhave boolean values (rather than None) if the field is a relation type\n(Field.is_relation=True).
Boolean flag that is True if the field has a many-to-many relation;\nFalse otherwise. The only field included with Django where this is\nTrue is ManyToManyField.
Boolean flag that is True if the field has a many-to-one relation, such\nas a ForeignKey; False otherwise.
Boolean flag that is True if the field has a one-to-many relation, such\nas a GenericRelation or the reverse of a ForeignKey; False\notherwise.
Boolean flag that is True if the field has a one-to-one relation, such\nas a OneToOneField; False otherwise.
Points to the model the field relates to. For example, Author in\nForeignKey(Author, on_delete=models.CASCADE). The related_model for\na GenericForeignKey is always None.