86 lines
2.9 KiB
ReStructuredText
86 lines
2.9 KiB
ReStructuredText
===================
|
|
Documents instances
|
|
===================
|
|
To create a new document object, create an instance of the relevant document
|
|
class, providing values for its fields as its constructor keyword arguments.
|
|
You may provide values for any of the fields on the document::
|
|
|
|
>>> page = Page(title="Test Page")
|
|
>>> page.title
|
|
'Test Page'
|
|
|
|
You may also assign values to the document's fields using standard object
|
|
attribute syntax::
|
|
|
|
>>> page.title = "Example Page"
|
|
>>> page.title
|
|
'Example Page'
|
|
|
|
Saving and deleting documents
|
|
=============================
|
|
MongoEngine tracks changes to documents to provide efficient saving. To save
|
|
the document to the database, call the :meth:`~mongoengine.Document.save` method.
|
|
If the document does not exist in the database, it will be created. If it does
|
|
already exist, then any changes will be updated atomically. For example::
|
|
|
|
>>> page = Page(title="Test Page")
|
|
>>> page.save() # Performs an insert
|
|
>>> page.title = "My Page"
|
|
>>> page.save() # Performs an atomic set on the title field.
|
|
|
|
.. note::
|
|
|
|
Changes to documents are tracked and on the whole perform `set` operations.
|
|
|
|
* ``list_field.pop(0)`` - *sets* the resulting list
|
|
* ``del(list_field)`` - *unsets* whole list
|
|
|
|
To delete a document, call the :meth:`~mongoengine.Document.delete` method.
|
|
Note that this will only work if the document exists in the database and has a
|
|
valide :attr:`id`.
|
|
|
|
.. seealso::
|
|
:ref:`guide-atomic-updates`
|
|
|
|
Document IDs
|
|
============
|
|
Each document in the database has a unique id. This may be accessed through the
|
|
:attr:`id` attribute on :class:`~mongoengine.Document` objects. Usually, the id
|
|
will be generated automatically by the database server when the object is save,
|
|
meaning that you may only access the :attr:`id` field once a document has been
|
|
saved::
|
|
|
|
>>> page = Page(title="Test Page")
|
|
>>> page.id
|
|
>>> page.save()
|
|
>>> page.id
|
|
ObjectId('123456789abcdef000000000')
|
|
|
|
Alternatively, you may define one of your own fields to be the document's
|
|
"primary key" by providing ``primary_key=True`` as a keyword argument to a
|
|
field's constructor. Under the hood, MongoEngine will use this field as the
|
|
:attr:`id`; in fact :attr:`id` is actually aliased to your primary key field so
|
|
you may still use :attr:`id` to access the primary key if you want::
|
|
|
|
>>> class User(Document):
|
|
... email = StringField(primary_key=True)
|
|
... name = StringField()
|
|
...
|
|
>>> bob = User(email='bob@example.com', name='Bob')
|
|
>>> bob.save()
|
|
>>> bob.id == bob.email == 'bob@example.com'
|
|
True
|
|
|
|
You can also access the document's "primary key" using the :attr:`pk` field; in
|
|
is an alias to :attr:`id`::
|
|
|
|
>>> page = Page(title="Another Test Page")
|
|
>>> page.save()
|
|
>>> page.id == page.pk
|
|
|
|
.. note::
|
|
|
|
If you define your own primary key field, the field implicitly becomes
|
|
required, so a :class:`ValidationError` will be thrown if you don't provide
|
|
it.
|