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[1.10.x] Made cosmetic edits to the "What happens when you save?" docs.

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Backport of e2112a5e1a from master
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Tim Graham
2016-12-17 10:24:08 -05:00
parent 0d019287ee
commit 2f95b91bbe
1 changed files with 19 additions and 26 deletions
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docs/ref/models/instances.txt
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@@ -413,43 +413,36 @@ What happens when you save?
When you save an object, Django performs the following steps: When you save an object, Django performs the following steps:
1. **Emit a pre-save signal.** The :doc:`signal </ref/signals>` #. **Emit a pre-save signal.** The :data:`~django.db.models.signals.pre_save`
:attr:`django.db.models.signals.pre_save` is sent, allowing any signal is sent, allowing any functions listening for that signal to do
functions listening for that signal to take some customized something.
action.
2. **Pre-process the data.** Each field on the object is asked to #. **Preprocess the data.** Each field's
perform any automated data modification that the field may need :meth:`~django.db.models.Field.pre_save` method is called to perform any
to perform. automated data modification that's needed. For example, the date/time fields
override ``pre_save()`` to implement
:attr:`~django.db.models.DateField.auto_now_add` and
:attr:`~django.db.models.DateField.auto_now`.
Most fields do *no* pre-processing — the field data is kept as-is. #. **Prepare the data for the database.** Each field's
Pre-processing is only used on fields that have special behavior. For :meth:`~django.db.models.Field.get_db_prep_save` method is asked to provide
example, if your model has a :class:`~django.db.models.DateField` with
``auto_now=True``, the pre-save phase will alter the data in the object
to ensure that the date field contains the current date stamp. (Our
documentation doesn't yet include a list of all the fields with this
"special behavior.")
3. **Prepare the data for the database.** Each field is asked to provide
its current value in a data type that can be written to the database. its current value in a data type that can be written to the database.
Most fields require *no* data preparation. Simple data types, such as Most fields don't require data preparation. Simple data types, such as
integers and strings, are 'ready to write' as a Python object. However, integers and strings, are 'ready to write' as a Python object. However, more
more complex data types often require some modification. complex data types often require some modification.
For example, :class:`~django.db.models.DateField` fields use a Python For example, :class:`~django.db.models.DateField` fields use a Python
``datetime`` object to store data. Databases don't store ``datetime`` ``datetime`` object to store data. Databases don't store ``datetime``
objects, so the field value must be converted into an ISO-compliant date objects, so the field value must be converted into an ISO-compliant date
string for insertion into the database. string for insertion into the database.
4. **Insert the data into the database.** The pre-processed, prepared #. **Insert the data into the database.** The preprocessed, prepared data is
data is then composed into an SQL statement for insertion into the composed into an SQL statement for insertion into the database.
database.
5. **Emit a post-save signal.** The signal #. **Emit a post-save signal.** The :data:`~django.db.models.signals.post_save`
:attr:`django.db.models.signals.post_save` is sent, allowing signal is sent, allowing any functions listening for that signal to do
any functions listening for that signal to take some customized something.
action.
How Django knows to UPDATE vs. INSERT How Django knows to UPDATE vs. INSERT
------------------------------------- -------------------------------------