Django:model类的objects属性
A model class's objects attribute is an instance of django.db.models.manager.Manager. A manager has the following methods, all of which return a QuerySet instance.
- all() -- Returns a QuerySet of all objects in the database. This is like the old get_list(). Takes no arguments.
- filter(**kwargs) -- Returns a QuerySet, filtered by the given keyword arguments. Lookup arguments are in the same style as previously, e.g. pubdate__year=2005, except you can leave off __exact as a convenience. For example, name='John' and name__exact='John' are equivalent. Note that for lookups between applications you can't omit __exact.
- exclude(**kwargs) is the same as filter(), but returns objects where the given arguments are not true.
- order_by(*fieldnames) -- Returns a QuerySet
- count() -- Returns the count of all objects in the database.
- dates(field_name, kind) -- Like the old get_FIELD_list() for date fields. For example, old-school get_pubdate_list('year') is now dates('pubdate', 'year').
- delete() -- Deletes all objects.
- distinct() -- Returns a QuerySet with DISTINCT set.
- extra(select=None, where=None, params=None, tables=None) -- Sets the select, where, paramsand tables arguments, which are in the same format as before.
- get(**kwargs) -- Like the old get_object(). Returns an object or raises DoesNotExist on error.
- in_bulk(id_list) -- Like the old get_in_bulk().
- iterator() -- Returns a generator that iterators over results.
- select_related() -- Returns a QuerySet with the "select related" option (which acts the same as before) set.
- values(*fieldnames) -- Like the old get_values().
Each QuerySet has the following methods, which return a clone of the query set with the appropriate changes made:
- filter(**kwargs)
- order_by(*fieldnames)
- iterator()
- count()
- get(**kwargs)
- delete()
- filter(**kwargs)
- select_related()
- order_by(*fieldnames)
- distinct()
- extra(select=None, where=None, params=None, tables=None)
Here are some examples, which use the following models:
class Reporter(models.Model):
fname = models.CharField(maxlength=30)
lname = models.CharField(maxlength=30)class Site(models.Model):
name = models.CharField(maxlength=20)class Article(models.Model):
headline = models.CharField(maxlength=50)
reporter = models.ForeignKey(Reporter)
pub_date = models.DateField()
sites = models.ManyToManyField(Site)Old syntax | New syntax |
|---|---|
reporters.get_list() | Reporter.objects.all() |
reporters.get_list(fname__exact='John') | Reporter.objects.filter(fname='John') |
reporters.get_list(order_by=('-lname', 'fname')) | Reporter.objects.order_by('-lname', 'fname') |
reporters.get_list(fname__exact='John', order_by=('lname',)) | Reporter.objects.filter(fname='John').order_by('lname') |
reporters.get_object(pk=3) | Reporter.objects.get(pk=3) |
reporters.get_object(complex=(Q(...)|Q(...))) | Reporter.objects.get(Q(...)|Q(...)) |
reporters.get_object(fname__contains='John') | Reporter.objects.get(fname__contains='John') |
reporters.get_list(fname__ne='John') | Reporter.objects.exclude(fname='John') (note that ne is no longer a valid lookup type) |
(not previously possible) | Reporter.objects.exclude(fname__contains='n') |
reporters.get_list(distinct=True) | Reporter.objects.distinct() |
reporters.get_list(offset=10, limit=5) | Reporter.objects.all()[10:15] |
reporters.get_values() | Reporter.objects.values() |
reporters.get_in_bulk([1, 2]) | Reporter.objects.in_bulk([1, 2]) |
reporters.get_in_bulk([1, 2], fname__exact='John') | Reporter.objects.filter(fname='John').in_bulk([1, 2]) |
Date lookup | |
articles.get_pub_date_list('year') | Article.objects.dates('pub_date', 'year') |
Latest-object lookup | |
articles.get_latest() (required get_latest_by in model) | Article.objects.latest() (with get_latest_by in model) |
(Not previously possible) | Article.objects.latest('pub_date') # Latest by pub_date (overrides get_latest_by field in model) |
Many-to-one related lookup | |
article_obj.reporter_id | article_obj.reporter.id |
article_obj.get_reporter() | article_obj.reporter |
reporter_obj.get_article_list() | reporter_obj.article_set.all() |
reporter_obj.get_article_list(headline__exact='Hello') | reporter_obj.article_set.filter(headline='Hello') |
reporter_obj.get_article_count() | reporter_obj.article_set.count() |
reporter_obj.add_article(headline='Foo') | reporter_obj.article_set.create(headline='Foo') |
(Alternate syntax) | reporter_obj.article_set.add(article_obj) |
("values" lookup, etc., not previously possible) | reporter_obj.article_set.values() |
Many-to-many related lookup | |
article_obj.get_site_list() | article_obj.sites.all() |
article_obj.set_sites([s1.id, s2.id]) | article_obj.sites.clear(); article_obj.sites.add(s1); article_obj.sites.add(s2) |
article_obj.set_sites([s1.id]) # deletion | article_obj.sites.remove(s2) |
site_obj.get_article_list() | site_obj.article_set.all() |
Note that related-object lookup uses the default manager of the related object, which means the API for accessing related objects is completely consistent with the API for accessing objects via a manager.
Also note that managers can't be accessed from instances:
p = Person.objects.get(pk=1)p.objects.all() # Raises AttributeErrorOverride default manager name ('objects') ¶
If a model already has an objects attribute, you'll need to specify an alternate name for theobjects manager.
class Person(models.Model):
first_name = models.CharField(maxlength=30)
last_name = models.CharField(maxlength=30)
objects = models.TextField()
people = models.Manager()p = Person(first_name='Mary', last_name='Jones', objects='Hello there.')p.save()p.objects == 'Hello there.'Person.people.all()