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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:
1. **Emit a pre-save signal.** The :doc:`signal </ref/signals>`
:attr:`django.db.models.signals.pre_save` is sent, allowing any
functions listening for that signal to take some customized
action.
#. **Emit a pre-save signal.** The :data:`~django.db.models.signals.pre_save`
signal is sent, allowing any functions listening for that signal to do
something.
2. **Pre-process the data.** Each field on the object is asked to
perform any automated data modification that the field may need
to perform.
#. **Preprocess the data.** Each field's
:meth:`~django.db.models.Field.pre_save` method is called to perform any
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.
Pre-processing is only used on fields that have special behavior. For
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
#. **Prepare the data for the database.** Each field's
:meth:`~django.db.models.Field.get_db_prep_save` method is asked to provide
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
integers and strings, are 'ready to write' as a Python object. However,
more complex data types often require some modification.
Most fields don't require data preparation. Simple data types, such as
integers and strings, are 'ready to write' as a Python object. However, more
complex data types often require some modification.
For example, :class:`~django.db.models.DateField` fields use a Python
``datetime`` object to store data. Databases don't store ``datetime``
objects, so the field value must be converted into an ISO-compliant date
string for insertion into the database.
4. **Insert the data into the database.** The pre-processed, prepared
data is then composed into an SQL statement for insertion into the
database.
#. **Insert the data into the database.** The preprocessed, prepared data is
composed into an SQL statement for insertion into the database.
5. **Emit a post-save signal.** The signal
:attr:`django.db.models.signals.post_save` is sent, allowing
any functions listening for that signal to take some customized
action.
#. **Emit a post-save signal.** The :data:`~django.db.models.signals.post_save`
signal is sent, allowing any functions listening for that signal to do
something.
How Django knows to UPDATE vs. INSERT
-------------------------------------