docs: add user guide

Author: kenjis

user_guide_src/source/changelogs/v4.5.0.rst

@@ -317,6 +317,12 @@ not changed.
 
 See :ref:`Using CodeIgniter’s Model <model-update-only-changed>` for details.
 
+Saving Dates
+------------
+
+Now you can configure the date/time format when you save :doc:`Time <../libraries/time>`
+instances. See :ref:`model-saving-dates` for details.
+
 Libraries
 =========
 

user_guide_src/source/database/configuration.rst

@@ -191,7 +191,8 @@ Explanation of Values:
                  * ``datetime-us`` - date and time with microsecond format
                  * ``time``        - time format
                  This can be used since v4.5.0, and you can get the value, e.g., ``$db->dateFormat['datetime']``.
-                 Currently, the database drivers do not use these values directly, but just provide the values.
+                 Currently, the database drivers do not use these values directly,
+                 but :ref:`Model <model-saving-dates>` uses them.
 ================ ===========================================================================================================
 
 .. _DateTime format: https://www.php.net/manual/en/datetime.format.php

user_guide_src/source/models/model.rst

@@ -458,6 +458,21 @@ model's ``save()`` method to inspect the class, grab any public and private prop
 .. note:: If you find yourself working with Entities a lot, CodeIgniter provides a built-in :doc:`Entity class </models/entities>`
     that provides several handy features that make developing Entities simpler.
 
+.. _model-saving-dates:
+
+Saving Dates
+------------
+
+.. versionadded:: 4.5.0
+
+When saving data, if you pass :doc:`Time <../libraries/time>` instances, they are
+converted to strings with the format defined in ``dateFormat['datetime']`` and
+``dateFormat['date']`` in the
+:ref:`database configuration <database-config-explanation-of-values>`.
+
+.. note:: Prior to v4.5.0, the date/time formats were hard coded as ``Y-m-d H:i:s``
+    and ``Y-m-d`` in the Model class.
+
 Deleting Data
 =============