_meta APILink para este cabeçalho#The model _meta API is at the core of the Django ORM. It enables other\nparts of the system such as lookups, queries, forms, and the admin to\nunderstand the capabilities of each model. The API is accessible through\nthe _meta attribute of each model class, which is an instance of an\ndjango.db.models.options.Options object.
Methods that it provides can be used to:
\nRetrieve all field instances of a model
Retrieve a single field instance of a model by name
Returns the field instance given a name of a field.
\nfield_name can be the name of a field on the model, a field\non an abstract or inherited model, or a field defined on another\nmodel that points to the model. In the latter case, the field_name\nwill be the related_name defined by the user or the name automatically\ngenerated by Django itself.
Hidden fields cannot be retrieved\nby name.
If a field with the given name is not found a\nFieldDoesNotExist exception will be\nraised.
>>> from django.contrib.auth.models import User\n\n# A field on the model\n>>> User._meta.get_field('username')\n<django.db.models.fields.CharField: username>\n\n# A field from another model that has a relation with the current model\n>>> User._meta.get_field('logentry')\n<ManyToOneRel: admin.logentry>\n\n# A non existent field\n>>> User._meta.get_field('does_not_exist')\nTraceback (most recent call last):\n ...\nFieldDoesNotExist: User has no field named 'does_not_exist'\nReturns a tuple of fields associated with a model. get_fields() accepts\ntwo parameters that can be used to control which fields are returned:
include_parentsTrue by default. Recursively includes fields defined on parent\nclasses. If set to False, get_fields() will only search for\nfields declared directly on the current model. Fields from models that\ndirectly inherit from abstract models or proxy classes are considered\nto be local, not on the parent.
include_hiddenFalse by default. If set to True, get_fields() will include\nfields that are used to back other field’s functionality. This will\nalso include any fields that have a related_name (such\nas ManyToManyField, or\nForeignKey) that start with a “+”.
>>> from django.contrib.auth.models import User\n>>> User._meta.get_fields()\n(<ManyToOneRel: admin.logentry>,\n <django.db.models.fields.AutoField: id>,\n <django.db.models.fields.CharField: password>,\n <django.db.models.fields.DateTimeField: last_login>,\n <django.db.models.fields.BooleanField: is_superuser>,\n <django.db.models.fields.CharField: username>,\n <django.db.models.fields.CharField: first_name>,\n <django.db.models.fields.CharField: last_name>,\n <django.db.models.fields.EmailField: email>,\n <django.db.models.fields.BooleanField: is_staff>,\n <django.db.models.fields.BooleanField: is_active>,\n <django.db.models.fields.DateTimeField: date_joined>,\n <django.db.models.fields.related.ManyToManyField: groups>,\n <django.db.models.fields.related.ManyToManyField: user_permissions>)\n\n# Also include hidden fields.\n>>> User._meta.get_fields(include_hidden=True)\n(<ManyToOneRel: auth.user_groups>,\n <ManyToOneRel: auth.user_user_permissions>,\n <ManyToOneRel: admin.logentry>,\n <django.db.models.fields.AutoField: id>,\n <django.db.models.fields.CharField: password>,\n <django.db.models.fields.DateTimeField: last_login>,\n <django.db.models.fields.BooleanField: is_superuser>,\n <django.db.models.fields.CharField: username>,\n <django.db.models.fields.CharField: first_name>,\n <django.db.models.fields.CharField: last_name>,\n <django.db.models.fields.EmailField: email>,\n <django.db.models.fields.BooleanField: is_staff>,\n <django.db.models.fields.BooleanField: is_active>,\n <django.db.models.fields.DateTimeField: date_joined>,\n <django.db.models.fields.related.ManyToManyField: groups>,\n <django.db.models.fields.related.ManyToManyField: user_permissions>)\nAs part of the formalization of the Model._meta API (from the\ndjango.db.models.options.Options class), a number of methods and\nproperties have been deprecated and will be removed in Django 1.10.
These old APIs can be replicated by either:
\ninvoking Options.get_field(), or;
invoking Options.get_fields() to retrieve a list of all\nfields, and then filtering this list using the field attributes that describe (or retrieve, in the case of\n_with_model variants) the properties of the desired fields.
Although it’s possible to make strictly equivalent replacements of the old\nmethods, that might not be the best approach. Taking the time to refactor any\nfield loops to make better use of the new API - and possibly include fields\nthat were previously excluded - will almost certainly result in better code.
\nAssuming you have a model named MyModel, the following substitutions\ncan be made to convert your code to the new API:
MyModel._meta.get_field(name) becomes:
f = MyModel._meta.get_field(name)\nthen check if:
\nf.auto_created == False, because the new get_field()\nAPI will find “reverse” relations, and:
f.is_relation and f.related_model is None, because the new\nget_field() API will find\nGenericForeignKey relations.
MyModel._meta.get_field_by_name(name) returns a tuple of these four\nvalues with the following replacements:
field can be found by MyModel._meta.get_field(name)
model can be found through the\nmodel attribute on the field.
direct can be found by: not field.auto_created or field.concrete
The auto_created check excludes\nall “forward” and “reverse” relations that are created by Django, but\nthis also includes AutoField and OneToOneField on proxy models.\nWe avoid filtering out these attributes using the\nconcrete attribute.
m2m can be found through the\nmany_to_many attribute on the field.
MyModel._meta.get_fields_with_model() becomes:
[\n (f, f.model if f.model != MyModel else None)\n for f in MyModel._meta.get_fields()\n if not f.is_relation\n or f.one_to_one\n or (f.many_to_one and f.related_model)\n]\nMyModel._meta.get_concrete_fields_with_model() becomes:
[\n (f, f.model if f.model != MyModel else None)\n for f in MyModel._meta.get_fields()\n if f.concrete and (\n not f.is_relation\n or f.one_to_one\n or (f.many_to_one and f.related_model)\n )\n]\nMyModel._meta.get_m2m_with_model() becomes:
[\n (f, f.model if f.model != MyModel else None)\n for f in MyModel._meta.get_fields()\n if f.many_to_many and not f.auto_created\n]\nMyModel._meta.get_all_related_objects() becomes:
[\n f for f in MyModel._meta.get_fields()\n if (f.one_to_many or f.one_to_one)\n and f.auto_created and not f.concrete\n]\nMyModel._meta.get_all_related_objects_with_model() becomes:
[\n (f, f.model if f.model != MyModel else None)\n for f in MyModel._meta.get_fields()\n if (f.one_to_many or f.one_to_one)\n and f.auto_created and not f.concrete\n]\nMyModel._meta.get_all_related_many_to_many_objects() becomes:
[\n f for f in MyModel._meta.get_fields(include_hidden=True)\n if f.many_to_many and f.auto_created\n]\nMyModel._meta.get_all_related_m2m_objects_with_model() becomes:
[\n (f, f.model if f.model != MyModel else None)\n for f in MyModel._meta.get_fields(include_hidden=True)\n if f.many_to_many and f.auto_created\n]\nMyModel._meta.get_all_field_names() becomes:
from itertools import chain\nlist(set(chain.from_iterable(\n (field.name, field.attname) if hasattr(field, 'attname') else (field.name,)\n for field in MyModel._meta.get_fields()\n # For complete backwards compatibility, you may want to exclude\n # GenericForeignKey from the results.\n if not (field.many_to_one and field.related_model is None)\n)))\nThis provides a 100% backwards compatible replacement, ensuring that both\nfield names and attribute names ForeignKeys are included, but fields\nassociated with GenericForeignKeys are not. A simpler version would be:
[f.name for f in MyModel._meta.get_fields()]\nWhile this isn’t 100% backwards compatible, it may be sufficient in many\nsituations.
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