The model _meta API is at the core of the Django ORM. It enables other parts of the system such as lookups, queries, forms, and the admin to understand the capabilities of each model. The API is accessible through the _meta attribute of each model class, which is an instance of an django.db.models.options.Options object.
Methods that it provides can be used to:
The Model _meta API has always existed as a Django internal, but wasn’t formally documented and supported. As part of the effort to make this API public, some of the already existing API entry points have changed slightly. A migration guide has been provided to assist in converting your code to use the new, official API.
Returns the field instance given a name of a field.
field_name can be the name of a field on the model, a field on an abstract or inherited model, or a field defined on another model that points to the model. In the latter case, the field_name will be the related_name defined by the user or the name automatically generated by Django itself.
Hidden fields cannot be retrieved by name.
If a field with the given name is not found a FieldDoesNotExist exception will be raised.
>>> from django.contrib.auth.models import User
# A field on the model
>>> User._meta.get_field('username')
<django.db.models.fields.CharField: username>
# A field from another model that has a relation with the current model
>>> User._meta.get_field('logentry')
<ManyToOneRel: admin.logentry>
# A non existent field
>>> User._meta.get_field('does_not_exist')
Traceback (most recent call last):
...
FieldDoesNotExist: User has no field named 'does_not_exist'
Не рекомендуется, начиная с версии 1.8: Options.get_field() previously accepted a many_to_many parameter which could be set to False to avoid searching ManyToManyFields. The old behavior has been preserved for backwards compatibility; however, the parameter and this behavior has been deprecated.
If you wish to filter out ManyToManyFields, you can inspect the Field.many_to_many attribute after calling get_field().
Returns a tuple of fields associated with a model. get_fields() accepts two parameters that can be used to control which fields are returned:
>>> from django.contrib.auth.models import User
>>> User._meta.get_fields()
(<ManyToOneRel: admin.logentry>,
<django.db.models.fields.AutoField: id>,
<django.db.models.fields.CharField: password>,
<django.db.models.fields.DateTimeField: last_login>,
<django.db.models.fields.BooleanField: is_superuser>,
<django.db.models.fields.CharField: username>,
<django.db.models.fields.CharField: first_name>,
<django.db.models.fields.CharField: last_name>,
<django.db.models.fields.EmailField: email>,
<django.db.models.fields.BooleanField: is_staff>,
<django.db.models.fields.BooleanField: is_active>,
<django.db.models.fields.DateTimeField: date_joined>,
<django.db.models.fields.related.ManyToManyField: groups>,
<django.db.models.fields.related.ManyToManyField: user_permissions>)
# Also include hidden fields.
>>> User._meta.get_fields(include_hidden=True)
(<ManyToOneRel: auth.user_groups>,
<ManyToOneRel: auth.user_user_permissions>,
<ManyToOneRel: admin.logentry>,
<django.db.models.fields.AutoField: id>,
<django.db.models.fields.CharField: password>,
<django.db.models.fields.DateTimeField: last_login>,
<django.db.models.fields.BooleanField: is_superuser>,
<django.db.models.fields.CharField: username>,
<django.db.models.fields.CharField: first_name>,
<django.db.models.fields.CharField: last_name>,
<django.db.models.fields.EmailField: email>,
<django.db.models.fields.BooleanField: is_staff>,
<django.db.models.fields.BooleanField: is_active>,
<django.db.models.fields.DateTimeField: date_joined>,
<django.db.models.fields.related.ManyToManyField: groups>,
<django.db.models.fields.related.ManyToManyField: user_permissions>)
As part of the formalization of the Model._meta API (from the django.db.models.options.Options class), a number of methods and properties have been deprecated and will be removed in Django 1.10.
These old APIs can be replicated by either:
Although it’s possible to make strictly equivalent replacements of the old methods, that might not be the best approach. Taking the time to refactor any field loops to make better use of the new API - and possibly include fields that were previously excluded - will almost certainly result in better code.
Assuming you have a model named MyModel, the following substitutions can be made to convert your code to the new API:
MyModel._meta.get_field(name):
f = MyModel._meta.get_field(name)
then check if:
MyModel._meta.get_field_by_name(name):
get_field_by_name() returned four values: (field, model, direct, m2m):
field can be found by MyModel._meta.get_field(name)
model can be found through the model attribute on the field.
direct can be found by: not field.auto_created or field.concrete
The auto_created check excludes all “forward” and “reverse” relations that are created by Django, but this also includes AutoField and OneToOneField on proxy models. We avoid filtering out these attributes using the concrete attribute.
m2m can be found through the many_to_many attribute on the field.
MyModel._meta.get_fields_with_model():
[
(f, f.model if f.model != MyModel else None)
for f in MyModel._meta.get_fields()
if not f.is_relation
or f.one_to_one
or (f.many_to_one and f.related_model)
]
MyModel._meta.get_concrete_fields_with_model():
[
(f, f.model if f.model != MyModel else None)
for f in MyModel._meta.get_fields()
if f.concrete and (
not f.is_relation
or f.one_to_one
or (f.many_to_one and f.related_model)
)
]
MyModel._meta.get_m2m_with_model():
[
(f, f.model if f.model != MyModel else None)
for f in MyModel._meta.get_fields()
if f.many_to_many and not f.auto_created
]
MyModel._meta.get_all_related_objects():
[
f for f in MyModel._meta.get_fields()
if (f.one_to_many or f.one_to_one) and f.auto_created
]
MyModel._meta.get_all_related_objects_with_model():
[
(f, f.model if f.model != MyModel else None)
for f in MyModel._meta.get_fields()
if (f.one_to_many or f.one_to_one) and f.auto_created
]
MyModel._meta.get_all_related_many_to_many_objects():
[
f for f in MyModel._meta.get_fields(include_hidden=True)
if f.many_to_many and f.auto_created
]
MyModel._meta.get_all_related_m2m_objects_with_model():
[
(f, f.model if f.model != MyModel else None)
for f in MyModel._meta.get_fields(include_hidden=True)
if f.many_to_many and f.auto_created
]
MyModel._meta.get_all_field_names():
from itertools import chain
list(set(chain.from_iterable(
(field.name, field.attname) if hasattr(field, 'attname') else (field.name,)
for field in MyModel._meta.get_fields()
# For complete backwards compatibility, you may want to exclude
# GenericForeignKey from the results.
if not (field.many_to_one and field.related_model is None)
)))
This provides a 100% backwards compatible replacement, ensuring that both field names and attribute names ForeignKeys are included, but fields associated with GenericForeignKeys are not. A simpler version would be:
[f.name for f in MyModel._meta.get_fields()]
While this isn’t 100% backwards compatible, it may be sufficient in many situations.
Mar 31, 2016