Merge pull request rails#48023 from p8/docs/headers-active-record

Add more missing headers to Active Record docs [ci-skip]

Author: p8

activerecord/lib/active_record/aggregations.rb

@@ -23,6 +23,8 @@ def init_internals
         @aggregation_cache = {}
       end
 
+      # = Active Record \Aggregations
+      #
       # Active Record implements aggregation through a macro-like class method called #composed_of
       # for representing attributes as value objects. It expresses relationships like "Account [is]
       # composed of Money [among other things]" or "Person [is] composed of [an] address". Each call

activerecord/lib/active_record/associations.rb

@@ -333,6 +333,8 @@ def association_instance_set(name, association)
         @association_cache[name] = association
       end
 
+      # = Active Record \Associations
+      #
       # \Associations are a set of macro-like class methods for tying objects together through
       # foreign keys. They express relationships like "Project has one Project Manager"
       # or "Project belongs to a Portfolio". Each macro adds a number of methods to the

activerecord/lib/active_record/attributes.rb

@@ -10,7 +10,7 @@ module Attributes
     included do
       class_attribute :attributes_to_define_after_schema_loads, instance_accessor: false, default: {} # :internal:
     end
-
+    # = Active Record \Attributes
     module ClassMethods
       # Defines an attribute with a type on this model. It will override the
       # type of existing attributes if needed. This allows control over how

activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb

@@ -5,7 +5,7 @@
 
 module ActiveRecord
   module ConnectionAdapters
-    # = Active Record Connection Adapters Connection Handler
+    # = Active Record Connection Handler
     #
     # ConnectionHandler is a collection of ConnectionPool objects. It is used
     # for keeping separate connection pools that connect to different databases.

activerecord/lib/active_record/connection_adapters/abstract_adapter.rb

@@ -13,6 +13,8 @@
 
 module ActiveRecord
   module ConnectionAdapters # :nodoc:
+    # = Active Record Abstract Adapter
+    #
     # Active Record supports multiple database systems. AbstractAdapter and
     # related classes form the abstraction layer which makes this possible.
     # An AbstractAdapter represents a connection to a database, and provides an

activerecord/lib/active_record/fixtures.rb

@@ -15,6 +15,8 @@ module ActiveRecord
   class FixtureClassNotFound < ActiveRecord::ActiveRecordError # :nodoc:
   end
 
+  # = Active Record \Fixtures
+  #
   # \Fixtures are a way of organizing data that you want to test against; in short, sample data.
   #
   # They are stored in YAML files, one file per model, which are placed in the directories

activerecord/lib/active_record/inheritance.rb

@@ -4,7 +4,7 @@
 require "active_support/core_ext/hash/indifferent_access"
 
 module ActiveRecord
-  # == Single table inheritance
+  # = Single table inheritance
   #
   # Active Record allows inheritance by storing the name of the class in a column that by
   # default is named "type" (can be changed by overwriting <tt>Base.inheritance_column</tt>).

activerecord/lib/active_record/locking/optimistic.rb

@@ -2,7 +2,7 @@
 
 module ActiveRecord
   module Locking
-    # == What is Optimistic Locking
+    # == What is \Optimistic \Locking
     #
     # Optimistic locking allows multiple users to access the same record for edits, and assumes a minimum of
     # conflicts with the data. It does this by checking whether another process has made changes to a record since

activerecord/lib/active_record/locking/pessimistic.rb

@@ -2,6 +2,8 @@
 
 module ActiveRecord
   module Locking
+    # = \Pessimistic \Locking
+    #
     # Locking::Pessimistic provides support for row-level locking using
     # SELECT ... FOR UPDATE and other lock types.
     #

activerecord/lib/active_record/middleware/database_selector.rb

@@ -4,6 +4,8 @@
 
 module ActiveRecord
   module Middleware
+    # = Database Selector \Middleware
+    #
     # The DatabaseSelector Middleware provides a framework for automatically
     # swapping from the primary to the replica database connection. Rails
     # provides a basic framework to determine when to swap and allows for