Model _meta API

• class Options
• The model _meta API is at the core of the Django ORM. It enables otherparts of the system such as lookups, queries, forms, and the admin tounderstand the capabilities of each model. The API is accessible throughthe _meta attribute of each model class, which is an instance of andjango.db.models.options.Options object.

Methods that it provides can be used to:

• Retrieve all field instances of a model
• Retrieve a single field instance of a model by name

Field access API

Retrieving a single field instance of a model by name

• Options.getfield(_field_name)
• Returns the field instance given a name of a field.

field_name can be the name of a field on the model, a fieldon an abstract or inherited model, or a field defined on anothermodel that points to the model. In the latter case, the field_namewill be (in order of preference) the related_query_nameset by the user, the related_name set by the user, orthe name automatically generated by Django.

Hidden fields cannot be retrievedby name.

If a field with the given name is not found aFieldDoesNotExist exception will beraised.

>>> 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'

Retrieving all field instances of a model

• Options.getfields(_include_parents=True, include_hidden=False)

• Returns a tuple of fields associated with a model. get_fields() acceptstwo parameters that can be used to control which fields are returned:

  • include_parents
  • True by default. Recursively includes fields defined on parentclasses. If set to False, get_fields() will only search forfields declared directly on the current model. Fields from models thatdirectly inherit from abstract models or proxy classes are consideredto be local, not on the parent.
  • include_hidden
  • False by default. If set to True, get_fields() will includefields that are used to back other field’s functionality. This willalso include any fields that have a related_name (suchas ManyToManyField, orForeignKey) that start with a “+”.

>>> 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>)