django官方文档——模型字段关系参考

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转自:http://docs.oneele.com/django/ref/models/fields.html#ref-foreignkey

Model field reference¶

This document contains all the gory details about all the field options and field types Django’s got to offer.

See also

If the built-in fields don’t do the trick, you can try django.contrib.localflavor, which contains assorted pieces of code that are useful for particular countries or cultures. Also, you can easilywrite your own custom model fields.

Note

Technically, these models are defined in django.db.models.fields, but for convenience they’re imported intodjango.db.models; the standard convention is to usefrom django.dbimport models and refer to fields asmodels.<Foo>Field.

Field options¶

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

null

Field.null

If True, Django will store empty values asNULL in the database. Default isFalse.

Note that empty string values will always get stored as empty strings, not as NULL. Only use null=True for non-string fields such as integers, booleans and dates. For both types of fields, you will also need to setblank=True if you wish to permit empty values in forms, as thenull parameter only affects database storage (seeblank).

Avoid using null on string-based fields such asCharField andTextField unless you have an excellent reason. If a string-based field hasnull=True, that means it has two possible values for “no data”:NULL, and the empty string. In most cases, it’s redundant to have two possible values for “no data;” Django convention is to use the empty string, notNULL.

Note

When using the Oracle database backend, the null=True option will be coerced for string-based fields that have the empty string as a possible value, and the valueNULL will be stored to denote the empty string.

blank

Field.blank

If True, the field is allowed to be blank. Default isFalse.

Note that this is different than null.null is purely database-related, whereasblank is validation-related. If a field hasblank=True, validation on Django’s admin site will allow entry of an empty value. If a field hasblank=False, the field will be required.

choices

Field.choices

An iterable (e.g., a list or tuple) of 2-tuples to use as choices for this field.

If this is given, Django’s admin will use a select box instead of the standard text field and will limit choices to the choices given.

A choices list looks like this:

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

The first element in each tuple is the actual value to be stored. The second element is the human-readable name for the option.

The choices list can be defined either as part of your model class:

class Foo(models.Model):    GENDER_CHOICES = (        ('M', 'Male'),        ('F', 'Female'),    )    gender = models.CharField(max_length=1, choices=GENDER_CHOICES)

or outside your model class altogether:

GENDER_CHOICES = (    ('M', 'Male'),    ('F', 'Female'),)class Foo(models.Model):    gender = models.CharField(max_length=1, choices=GENDER_CHOICES)

You can also collect your available choices into named groups that can be used for organizational purposes:

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).

For each model field that has choices set, Django will add a method to retrieve the human-readable name for the field's current value. Seeget_FOO_display() in the database API documentation.

Finally, note that choices can be any iterable object -- not necessarily a list or tuple. This lets you construct choices dynamically. But if you find yourself hackingchoices to be dynamic, you're probably better off using a proper database table with aForeignKey.choices is meant for static data that doesn't change much, if ever.

db_column

Field.db_column

The name of the database column to use for this field. If this isn't given, Django will use the field's name.

If your database column name is an SQL reserved word, or contains characters that aren't allowed in Python variable names -- notably, the hyphen -- that's OK. Django quotes column and table names behind the scenes.

db_index

Field.db_index

If True, djadmin:django-admin.py sqlindexes <sqlindexes> will output aCREATE INDEX statement for this field.

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'sDEFAULT_INDEX_TABLESPACE setting, if set, or thedb_tablespace of the model, if any. If the backend doesn't support tablespaces, this option is ignored.

default

Field.default

The default value for the field. This can be a value or a callable object. If callable it will be called every time a new object is created.

editable

Field.editable

If False, the field will not be editable in the admin or via forms automatically generated from the model class. Default isTrue.

error_messages

New in Django 1.2: Please, see the release notes
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.

help_text

Field.help_text

Extra "help" text to be displayed under the field on the object's admin form. It's useful for documentation even if your object doesn't have an admin form.

Note that this value is not HTML-escaped when it's displayed in the admin interface. This lets you include HTML inhelp_text if you so desire. For example:

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.

primary_key

Field.primary_key

If True, this field is the primary key for the model.

If you don't specify primary_key=True for any fields in your model, Django will automatically add anIntegerField to hold the primary key, so you don't need to setprimary_key=True on any of your fields unless you want to override the default primary-key behavior. For more, see自动主键字段.

primary_key=True impliesnull=False andunique=True. Only one primary key is allowed on an object.

unique

Field.unique

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

This is enforced at the database level and at the Django admin-form level. If you try to save a model with a duplicate value in aunique field, adjango.db.IntegrityError will be raised by the model'ssave() method.

This option is valid on all field types except ManyToManyField andFileField.

unique_for_date

Field.unique_for_date

Set this to the name of a DateField orDateTimeField to require that this field be unique for the value of the date field.

For example, if you have a field title that hasunique_for_date="pub_date", then Django wouldn't allow the entry of two records with the sametitle and pub_date.

This is enforced at the Django admin-form level but not at the database level.

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 andunique_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. SeeVerbose field names.

validators

New in Django 1.2: Please, see the release notes
Field.validators

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

Field types¶

AutoField

class AutoField(**options

An IntegerField that automatically increments according to available IDs. You usually won't need to use this directly; a primary key field will automatically be added to your model if you don't specify otherwise. See 自动主键字段.

BigIntegerField

New in Django 1.2: Please, see the release notes
classBigIntegerField([**options]

A 64 bit integer, much like an IntegerField except that it is guaranteed to fit numbers from -9223372036854775808 to 9223372036854775807. The admin represents this as an<input type="text"> (a single-line input).

BooleanField

classBooleanField(**options

A true/false field.

The admin represents this as a checkbox.

Changed in Django 1.2: Please, see the release notes

CharField

class CharField(max_length=None[,**options]

A string field, for small- to large-sized strings.

For large amounts of text, use TextField.

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

CharField has one extra required argument:

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.

Note

If you are writing an application that must be portable to multiple database backends, you should be aware that there are restrictions onmax_length for some backends. Refer to thedatabase backend notes for details.

MySQL users

If you are using this field with MySQLdb 1.2.2 and the utf8_bin collation (which is not the default), there are some issues to be aware of. Refer to theMySQL database notes for details.

CommaSeparatedIntegerField

classCommaSeparatedIntegerField(max_length=None[,**options]

A field of integers separated by commas. As in CharField, themax_length argument is required and the note about database portability mentioned there should be heeded.

DateField

class DateField([auto_now=False,auto_now_add=False, **options]

A date, represented in Python by a datetime.date instance. Has a few extra, optional arguments:

DateField.auto_now

Automatically set the field to now every time the object is saved. Useful for "last-modified" timestamps. Note that the current date isalways used; it's not just a default value that you can override.

DateField.auto_now_add

Automatically set the field to now when the object is first created. Useful for creation of timestamps. Note that the current date isalways used; it's not just a default value that you can override.

The admin represents this as an <inputtype="text"> with a JavaScript calendar, and a shortcut for "Today". The JavaScript calendar will always start the week on a Sunday.

Note

As currently implemented, setting auto_now orauto_now_add to True will cause the field to have editable=False and blank=True set.

DateTimeField

classDateTimeField([auto_now=False,auto_now_add=False, **options]

A date and time, represented in Python by a datetime.datetime instance. Takes the same extra arguments asDateField.

The admin represents this as two <inputtype="text"> fields, with JavaScript shortcuts.

DecimalField

classDecimalField(max_digits=None, decimal_places=None[,**options]

A fixed-precision decimal number, represented in Python by a Decimal instance. Has two required arguments:

DecimalField.max_digits

The maximum number of digits allowed in the number. Note that this number must be greater thandecimal_places, if it exists.

DecimalField.decimal_places

The number of decimal places to store with the number.

For example, to store numbers up to 999 with a resolution of 2 decimal places, you'd use:

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

And to store numbers up to approximately one billion with a resolution of 10 decimal places:

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

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

Note

For more information about the differences between the FloatField andDecimalField classes, please seeFloatField vs. DecimalField.

EmailField

classEmailField([max_length=75,**options]

A CharField that checks that the value is a valid e-mail address.

FileField

class FileField(upload_to=None[,max_length=100, **options]

A file-upload field.

Note

The primary_key andunique arguments are not supported, and will raise aTypeError if used.

Has one required argument:

FileField.upload_to

A local filesystem path that will be appended to your MEDIA_ROOT setting to determine the value of theurl attribute.

This path may contain strftime formatting, which will be replaced by the date/time of the file upload (so that uploaded files don't fill up the given directory).

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

ArgumentDescriptioninstance

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 defaultAutoField, it might not yet have a value for its primary key field.

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

Also has one optional argument:

FileField.storage

Optional. A storage object, which handles the storage and retrieval of your files. See管理文件 for details on how to provide this object.

The admin represents this field as an <inputtype="file"> (a file-upload widget).

Using a FileField or anImageField (see below) in a model takes a few steps:

  1. In your settings file, you'll need to define MEDIA_ROOT as the full path to a directory where you'd like Django to store uploaded files. (For performance, these files are not stored in the database.) DefineMEDIA_URL as the base public URL of that directory. Make sure that this directory is writable by the Web server's user account.
  2. Add the FileField orImageField to your model, making sure to define theupload_to option to tell Django to which subdirectory ofMEDIA_ROOT it should upload files.
  3. All that will be stored in your database is a path to the file (relative to MEDIA_ROOT). You'll most likely want to use the convenienceurl function provided by Django. For example, if yourImageField is calledmug_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 isstrftime 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 thename andsize attributes respectively; for more information on the available attributes and methods, see theFile class reference and the管理文件 topic guide.

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

By default, FileField instances are created asvarchar(100) columns in your database. As with other fields, you can change the maximum length using themax_length argument.

FileField and FieldFile¶

When you access a FileField on a model, you are given an instance ofFieldFile as a proxy for accessing the underlying file. This class has several methods that can be used to interact with file data:

FieldFile.open(mode='rb'

Behaves like the standard Python open() method and opens the file associated with this instance in the mode specified bymode.

FieldFile.close()¶

Behaves like the standard Python file.close() method and closes the file associated with this instance.

FieldFile.save(name,content, save=True

This method takes a filename and file contents and passes them to the storage class for the field, then associates the stored file with the model field. If you want to manually associate file data withFileField instances on your model, thesave() method is used to persist that file data.

Takes two required arguments: name which is the name of the file, andcontent which is a file-like object containing the file's contents. The optionalsave argument controls whether or not the instance is saved after the file has been altered. Defaults toTrue.

FieldFile.delete(save=True

Deletes the file associated with this instance and clears all attributes on the field. Note: This method will close the file if it happens to be open whendelete() is called.

The optional save argument controls whether or not the instance is saved after the file has been deleted. Defaults toTrue.

FilePathField

classFilePathField(path=None[,match=None, recursive=False, max_length=100, **options]

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

FilePathField.path

Required. The absolute filesystem path to a directory from which this FilePathField should get its choices. Example:"/home/images".

FilePathField.match

Optional. A regular expression, as a string, that FilePathField will use to filter filenames. Note that the regex will be applied to the base filename, not the full path. Example:"foo.*\.txt$", which will match a file calledfoo23.txt but not bar.txt or foo23.gif.

FilePathField.recursive

Optional. Either True orFalse. Default isFalse. Specifies whether all subdirectories ofpath should be included

Of course, these arguments can be used together.

The one potential gotcha is that match applies to the base filename, not the full path. So, this example:

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

...will match /home/images/foo.gif but not/home/images/foo/bar.gif because thematch applies to the base filename (foo.gif andbar.gif).

By default, FilePathField instances are created asvarchar(100) columns in your database. As with other fields, you can change the maximum length using themax_length argument.

FloatField

classFloatField([**options]

A floating-point number represented in Python by a float instance.

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

FloatField vs.DecimalField

The FloatField class is sometimes mixed up with theDecimalField class. Although they both represent real numbers, they represent those numbers differently.FloatField uses Python'sfloat type internally, whileDecimalField uses Python'sDecimal type. For information on the difference between the two, see Python's documentation onDecimal fixed point and floating point arithmetic.

ImageField

classImageField(upload_to=None[,height_field=None, width_field=None, max_length=100, **options]

Inherits all attributes and methods from FileField, but also validates that the uploaded object is a valid image.

In addition to the special attributes that are available for FileField, anImageField also hasheight andwidth attributes.

To facilitate querying on those attributes, ImageField has two extra optional arguments:

ImageField.height_field

Name of a model field which will be auto-populated with the height of the image each time the model instance is saved.

ImageField.width_field

Name of a model field which will be auto-populated with the width of the image each time the model instance is saved.

Requires the Python Imaging Library.

By default, ImageField instances are created asvarchar(100) columns in your database. As with other fields, you can change the maximum length using themax_length argument.

IntegerField

classIntegerField([**options]

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

IPAddressField

classIPAddressField([**options]

An IP address, in string format (e.g. "192.0.2.30"). The admin represents this as an<input type="text"> (a single-line input).

NullBooleanField

classNullBooleanField([**options]

Like a BooleanField, but allowsNULL as one of the options. Use this instead of aBooleanField withnull=True. The admin represents this as a<select> box with "Unknown", "Yes" and "No" choices.

PositiveIntegerField

classPositiveIntegerField([**options]

Like an IntegerField, but must be positive.

PositiveSmallIntegerField

classPositiveSmallIntegerField([**options]

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

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.

Like a CharField, you can specify max_length (read the note about database portability andmax_length in that section, too). Ifmax_length is not specified, Django will use a default length of 50.

Implies setting Field.db_index toTrue.

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 usingprepopulated_fields.

SmallIntegerField

classSmallIntegerField([**options]

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

TextField

class TextField([**options]

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

MySQL users

If you are using this field with MySQLdb 1.2.1p2 and the utf8_bin collation (which is not the default), there are some issues to be aware of. Refer to theMySQL database notes for details.

TimeField

class TimeField([auto_now=False,auto_now_add=False, **options]

A time, represented in Python by a datetime.time instance. Accepts the same auto-population options asDateField.

The admin represents this as an <inputtype="text"> with some JavaScript shortcuts.

URLField

class URLField([verify_exists=True,max_length=200, **options]

A CharField for a URL. Has one extra optional argument:

URLField.verify_exists

If True (the default), the URL given will be checked for existence (i.e., the URL actually loads and doesn't give a 404 response).

Note that when you're using the single-threaded development server, validating a URL being served by the same server will hang. This should not be a problem for multithreaded servers.

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

Like all CharField subclasses,URLField takes the optionalmax_length, a default of 200 is used.

XMLField

Deprecated in Django 1.3: XMLField is deprecated. Use TextField instead.
class XMLField(schema_path=None[,**options]

A TextField that stores XML data and a path to a schema. Takes one optional argument:

schema_path

The filesystem path to a schema for the field.

Relationship fields¶

Django also defines a set of fields that represent relations.

ForeignKey

classForeignKey(othermodel[,**options]

A many-to-one relationship. Requires a positional argument: the class to which the model is related.

To create a recursive relationship -- an object that has a many-to-one relationship with itself -- usemodels.ForeignKey('self').

If you need to create a relationship on a model that has not yet been defined, you can use the name of the model, rather than the model object itself:

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

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

class Car(models.Model):    manufacturer = models.ForeignKey('production.Manufacturer')

This sort of reference can be useful when resolving circular import dependencies between two applications.

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 theCar model will have a manufacturer_id column. (You can change this explicitly by specifyingdb_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.

Arguments¶

ForeignKey accepts an extra set of arguments -- all optional -- that define the details of how the relation works.

ForeignKey.limit_choices_to

A dictionary of lookup arguments and values (see 构造查询) that limit the available admin choices for this object. Use this with functions from the Pythondatetime module to limit choices of objects by date. For example:

limit_choices_to = {'pub_date__lte': datetime.now}

only allows the choice of related objects with a pub_date before the current date/time to be chosen.

Instead of a dictionary this can also be a Q object for more complex queries. However, if limit_choices_to is aQ object then it will only have an effect on the choices available in the admin when the field is not listed inraw_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. See therelated objects documentation for a full explanation and example. Note that you must set this value when defining relations onabstract models; and when you do so some special syntax is available.

If you'd prefer Django didn't create a backwards relation, set related_name to '+'. For example, this will ensure that theUser model won't get a backwards relation to this model:

user = models.ForeignKey(User, related_name='+')
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.

New in Django Development version.
ForeignKey.on_delete

When an object referenced by a ForeignKey is deleted, Django by default emulates the behavior of the SQL constraintON DELETECASCADE and also deletes the object containing the ForeignKey. This behavior can be overridden by specifying theon_delete argument. For example, if you have a nullableForeignKey and you want it to be set null when the referenced object is deleted:

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

The possible values for on_delete are found indjango.db.models:

  • CASCADE: Cascade deletes; the default.

  • PROTECT: Prevent deletion of the referenced object by raisingdjango.db.models.ProtectedError, a subclass ofdjango.db.IntegrityError.

  • SET_NULL: Set theForeignKey null; this is only possible ifnull isTrue.

  • SET_DEFAULT: Set theForeignKey to its default value; a default for theForeignKey must be set.

  • SET(): Set theForeignKey to the value passed toSET(), 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:

    def get_sentinel_user():    return User.objects.get_or_create(username='deleted')[0]class MyModel(models.Model):    user = models.ForeignKey(User, on_delete=models.SET(get_sentinel_user))
  • DO_NOTHING: Take no action. If your database backend enforces referential integrity, this will cause anIntegrityError unless you manually add a SQLON DELETE constraint to the database field (perhaps usinginitial sql).

ManyToManyField

classManyToManyField(othermodel[,**options]

A many-to-many relationship. Requires a positional argument: the class to which the model is related. This works exactly the same as it does forForeignKey, including all the options regardingrecursive and lazy relationships.

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 model that contains it. Since some databases don't support table names above a certain length, these table names will be automatically truncated to 64 characters and a uniqueness hash will be used. This means you might see table names likeauthor_books_9cdf4; this is perfectly normal. You can manually provide the name of the join table using thedb_table option.

Arguments¶

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

ManyToManyField.related_name

Same as ForeignKey.related_name.

ManyToManyField.limit_choices_to

Same as ForeignKey.limit_choices_to.

limit_choices_to has no effect when used on aManyToManyField with a custom intermediate table specified using thethrough parameter.

ManyToManyField.symmetrical

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

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 aperson_set attribute to thePerson class. Instead, theManyToManyField 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 toFalse. This will force Django to add the descriptor for the reverse relationship, allowingManyToManyField 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 thethrough 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.

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 two tables being joined.

OneToOneField

classOneToOneField(othermodel[,parent_link=False, **options]

A one-to-one relationship. Conceptually, this is similar to a ForeignKey withunique=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;多表继承 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 forForeignKey, including all the options regardingrecursive and lazy relationships.

Additionally, OneToOneField accepts all of the extra arguments accepted byForeignKey, 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 extraOneToOneField which would normally be implicitly created by subclassing.

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