问题
Given a Django model, I'm trying to list all of its fields. I've seen some examples of doing this using the _meta model attribute, but doesn't the underscore in front of meta indicate that the _meta attribute is a private attribute and shouldn't be accessed directly? ... Because, for example, the layout of _meta could change in the future and not be a stable API?
Is _meta an exception to this rule? Is it stable and ready to use or is it considered bad practice to access it? Or is there a function or some other way to introspect the fields of a model without using the _meta attribute? Below is a list of some links showing how to do this using the _meta attribute
Any advice is much appreciated.
django object get/set field
http://www.djangofoo.com/80/get-list-model-fields
How to introspect django model fields?
回答1:
_meta is private, but it's relatively stable. There are efforts to formalise it, document it and remove the underscore, which might happen before 1.3 or 1.4. I imagine effort will be made to ensure things are backwards compatible, because lots of people have been using it anyway.
If you're particularly concerned about compatibility, write a function that takes a model and returns the fields. This means if something does change in the future, you only have to change one function.
def get_model_fields(model):
return model._meta.fields
I believe this will return a list of Field objects. To get the value of each field from the instance, use getattr(instance, field.name).
Update: Django contributors are working on an API to replace the _Meta object as part of a Google Summer of Code. See:
- https://groups.google.com/forum/#!topic/django-developers/hD4roZq0wyk
- https://code.djangoproject.com/wiki/new_meta_api
回答2:
I know this post is pretty old, but I just cared to tell anyone who is searching for the same thing that there is a public and official API to do this: get_fields() and get_field()
Usage:
fields = model._meta.get_fields()
my_field = model._meta.get_field('my_field')
https://docs.djangoproject.com/en/1.8/ref/models/meta/
回答3:
This is something that is done by Django itself when building a form from a model. It is using the _meta attribute, but as Bernhard noted, it uses both _meta.fields and _meta.many_to_many. Looking at django.forms.models.fields_for_model, this is how you could do it:
opts = model._meta
for f in sorted(opts.fields + opts.many_to_many):
print '%s: %s' % (f.name, f)
回答4:
Now there is special method - get_fields()
>>> from django.contrib.auth.models import User
>>> User._meta.get_fields()
It accepts two parameters that can be used to control which fields are returned:
include_parents
True by default. Recursively includes fields defined on parent classes. If set to False, get_fields() will only search for fields declared directly on the current model. Fields from models that directly inherit from abstract models or proxy classes are considered to be local, not on the parent.
include_hidden
False by default. If set to True, get_fields() will include fields that are used to back other field’s functionality. This will also include any fields that have a related_name (such as ManyToManyField, or ForeignKey) that start with a “+”
回答5:
get_fields() returns a tuple and each element is a Model field type, which can't be used directly as a string. So, field.name will return the field name
my_model_fields = [field.name for field in MyModel._meta.get_fields()]
The above code will return a list conatining all fields name
Example
In [11]: from django.contrib.auth.models import User
In [12]: User._meta.get_fields()
Out[12]:
(<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>)
In [13]: [field.name for field in User._meta.get_fields()]
Out[13]:
['logentry',
'id',
'password',
'last_login',
'is_superuser',
'username',
'first_name',
'last_name',
'email',
'is_staff',
'is_active',
'date_joined',
'groups',
'user_permissions']
回答6:
The model fields contained by _meta are listed in multiple locations as lists of the respective field objects. It may be easier to work with them as a dictionary where the keys are the field names.
In my opinion, this is most irredundant and expressive way to collect and organize the model field objects:
def get_model_fields(model):
fields = {}
options = model._meta
for field in sorted(options.concrete_fields + options.many_to_many + options.virtual_fields):
fields[field.name] = field
return fields
(See This example usage in django.forms.models.fields_for_model.)
回答7:
How about this one.
fields = Model._meta.fields
回答8:
As per the django documentation 2.2 you can use:
To get all fields: Model._meta.get_fields()
To get an individual field: Model._meta.get_field('field name')
ex. Session._meta.get_field('expire_date')
回答9:
If you need this for your admin site, there is also the ModelAdmin.get_fields method (docs), which returns a list of field name strings.
For example:
class MyModelAdmin(admin.ModelAdmin):
# extending change_view, just as an example
def change_view(self, request, object_id=None, form_url='', extra_context=None):
# get the model field names
field_names = self.get_fields(request)
# use the field names
...
回答10:
Another way is add functions to the model and when you want to override the date you can call the function.
class MyModel(models.Model):
name = models.CharField(max_length=256)
created = models.DateTimeField(auto_now_add=True)
modified = models.DateTimeField(auto_now=True)
def set_created_date(self, created_date):
field = self._meta.get_field('created')
field.auto_now_add = False
self.created = created_date
def set_modified_date(self, modified_date):
field = self._meta.get_field('modified')
field.auto_now = False
self.modified = modified_date
my_model = MyModel(name='test')
my_model.set_modified_date(new_date)
my_model.set_created_date(new_date)
my_model.save()
来源：https://stackoverflow.com/questions/3647805/get-models-fields-in-django