MONGOID-5467 MONGOID-5320 Change usage of ActiveModel::MissingAttributeError to Mongoid::Errors:AttributeNotLoaded (#5437)

* Change usage of ActiveModel::MissingAttributeError to Mongoid::Errors::AttributeNotLoaded.

* Fix specs

* Improve release notes

Co-authored-by: shields <[email protected]>

Author: johnnyshields

source/reference/crud.txt

@@ -657,7 +657,7 @@ Mongoid provides several ways of accessing field values.
 .. note::
 
   All of the access methods described below raise
-  ``ActiveModel::MissingAttributeError`` when the field being accessed is
+  ``Mongoid::Errors::AttributeNotLoaded`` when the field being accessed is
   :ref:`projected out <projection>`, either by virtue of not being included in
   :ref:`only <only>` or by virtue of being included in
   :ref:`without <without>`. This applies to both reads and writes.

source/reference/queries.txt

@@ -775,12 +775,12 @@ operation is sometimes called "projection".
   band = Band.only(:name).first
 
 Attempting to reference attributes which have not been loaded results in
-``ActiveModel::MissingAttributeError``.
+``Mongoid::Errors::AttributeNotLoaded``.
 
 .. code-block:: ruby
 
   band.label
-  # ActiveModel::MissingAttributeError (Missing attribute: 'label'.)
+  #=> raises Mongoid::Errors::AttributeNotLoaded
 
 Even though Mongoid currently allows writing to attributes that have not
 been loaded, such writes will not be persisted

source/release-notes/mongoid-9.0.txt

@@ -0,0 +1,42 @@
+***********
+Mongoid 9.0
+***********
+
+.. default-domain:: mongodb
+
+.. contents:: On this page
+   :local:
+   :backlinks: none
+   :depth: 2
+   :class: singlecol
+
+This page describes significant changes and improvements in Mongoid 9.0.
+The complete list of releases is available `on GitHub
+<https://github.com/mongodb/mongoid/releases>`_ and `in JIRA
+<https://jira.mongodb.org/projects/MONGOID?selectedItem=com.atlassian.jira.jira-projects-plugin:release-page>`_;
+please consult GitHub releases for detailed release notes and JIRA for
+the complete list of issues fixed in each release, including bug fixes.
+
+
+Raise AttributeNotLoaded error when accessing fields omitted from query projection
+----------------------------------------------------------------------------------
+
+When attempting to access a field on a model instance which was
+excluded with the ``.only`` or ``.without`` query projections methods
+when the instance was loaded, Mongoid will now raise a
+``Mongoid::Errors::AttributeNotLoaded`` error.
+
+.. code-block:: ruby
+
+  Band.only(:name).first.label
+  #=> raises Mongoid::Errors::AttributeNotLoaded
+
+  Band.without(:label).first.label = 'Sub Pop Records'
+  #=> raises Mongoid::Errors::AttributeNotLoaded
+
+In earlier Mongoid versions, the same conditions would raise an
+``ActiveModel::MissingAttributeError``. Please check your code for
+any Mongoid-specific usages of this class, and change them to
+``Mongoid::Errors::AttributeNotLoaded``. Note additionally that
+``AttributeNotLoaded`` inherits from ``Mongoid::Errors::MongoidError``,
+while ``ActiveModel::MissingAttributeError`` does not.