MONGOID-5151 Respect aliased fields in pluck/distinct by having Document.database_field_name recursively consider embedded docs (#5047)

* MONGOID-???? database_field_name should work with embedded fields

database_field_name does not currently handle "." delimiter char.
As an improvement, it should consider embedded doc "store_as" and
embedded field aliases.

This is a precursor to further improvements on "distinct" and "pluck" methods.

* add integration tests

* add documentation

* add release note

* relations -> associations

* mark private

* replace freezes with dup

* Comment out the where test

* relations -> associations

* remove commented out test

Co-authored-by: shields <[email protected]>
Co-authored-by: Oleg Pudeyev <[email protected]>
Co-authored-by: Dmitry Rybakov <[email protected]>

Author: 3 people

source/reference/queries.txt

@@ -1324,6 +1324,12 @@ Mongoid also has some helpful methods on criteria.
 
        *Get a list of distinct values for a single field. Note this will always hit
        the database for the distinct values.*
+       
+       *This method accepts the dot notation, thus permitting referencing
+       fields in embedded associations.*
+       
+       *This method respects :ref:`field aliases <field-aliases>`,
+       including those defined in embedded documents.*
 
      -
         .. code-block:: ruby
@@ -1332,6 +1338,18 @@ Mongoid also has some helpful methods on criteria.
           Band.where(:fans.gt => 100000).
             distinct(:name)
 
+          Band.distinct('cities.name')
+          
+          # Assuming an aliased field:
+          class Manager
+            include Mongoid::Document
+            embedded_in :band
+            field :name, as: :n
+          end
+          
+          # Expands out to "managers.name" in the query:
+          Band.distinct('managers.n')
+
    * - ``Criteria#each``
 
        *Iterate over all matching documents in the criteria.*
@@ -1477,12 +1495,24 @@ Mongoid also has some helpful methods on criteria.
 
        *Get all the values for the provided field.
        Returns nil for unset fields and for non-existent fields.*
+       
+       *This method accepts the dot notation, thus permitting referencing
+       fields in embedded associations.*
+       
+       *This method respects :ref:`field aliases <field-aliases>`,
+       including those defined in embedded documents.*
 
      -
         .. code-block:: ruby
 
           Band.all.pluck(:name)
 
+          Band.all.pluck('cities.name')
+
+          # Using the earlier definition of Manager,
+          # expands out to "managers.name" in the query:
+          Band.all.pluck('managers.n')
+
 
 Eager Loading
 =============

source/release-notes/mongoid-7.4.txt

@@ -111,3 +111,43 @@ which is `under consideration <https://jira.mongodb.org/browse/MONGOID-5158>`_,
 Mongoid 7.4 and later will inherit the new implementation provided by
 ``bson-ruby`` while Mongoid 7.3 and earlier will continue with the
 implementation returning a hash of ``{"$oid" => "..."}``.
+
+
+``distinct`` and ``pluck`` Respect Field Aliases In Embedded Documents
+----------------------------------------------------------------------
+
+When ``distinct`` and ``pluck`` are used with aliased fields in embedded
+documents, the aliases are now expanded. Given the following definitions:
+
+.. code-block:: ruby
+
+  class Band
+    include Mongoid::Document
+    embeds_many :managers
+  end
+  
+  class Manager
+    include Mongoid::Document
+    embedded_in :band
+    
+    field :name, as: :n
+  end
+
+Mongoid 7.4 behavior:
+
+.. code-block:: ruby
+
+  # Expands out to "managers.name" in the query:
+  Band.distinct('managers.n')
+  Band.pluck('managers.n')
+
+Mongoid 7.3 behavior:
+
+.. code-block:: ruby
+
+  # Sends "managers.n" without expanding the alias:
+  Band.distinct('managers.n')
+  Band.pluck('managers.n')
+
+Note that the alias expansion for top-level fields has already been
+done by Mongoid 7.3.