Add support for virtual depth column

still need to consider whether to keep depth_cache_column as deprecated

Author: kbrock

lib/ancestry/has_ancestry.rb

@@ -70,26 +70,30 @@ def has_ancestry options = {}
 
       # Create ancestry column accessor and set to option or default
       if options[:cache_depth]
-        # Create accessor for column name and set to option or default
-        self.cattr_accessor :depth_cache_column
-        self.depth_cache_column =
-          if options[:cache_depth] == true
-            options[:depth_cache_column]&.to_s || 'ancestry_depth'
-          else
-            options[:cache_depth].to_s
+        if options[:cache_depth] == :virtual
+          # NOTE: not setting self.depth_cache_column so the code does not try to update the column
+          depth_cache_sql = options[:depth_cache_column]&.to_s || 'ancestry_depth'
+        else
+          # Create accessor for column name and set to option or default
+          self.cattr_accessor :depth_cache_column
+          self.depth_cache_column =
+            if options[:cache_depth] == true
+              options[:depth_cache_column]&.to_s || 'ancestry_depth'
+            else
+              options[:cache_depth].to_s
+            end
+          if options[:depth_cache_column]
+            ActiveSupport::Deprecation.warn("has_ancestry :depth_cache_column is deprecated. Use :cache_depth instead.")
           end
-        if options[:depth_cache_column]
-          ActiveSupport::Deprecation.warn("has_ancestry :depth_cache_column is deprecated. Use :cache_depth instead.")
-        end
-
-        # Cache depth in depth cache column before save
-        before_validation :cache_depth
-        before_save :cache_depth
 
-        # Validate depth column
-        validates_numericality_of depth_cache_column, :greater_than_or_equal_to => 0, :only_integer => true, :allow_nil => false
+          # Cache depth in depth cache column before save
+          before_validation :cache_depth
+          before_save :cache_depth
 
-        depth_cache_sql = depth_cache_column
+          # Validate depth column
+          validates_numericality_of depth_cache_column, :greater_than_or_equal_to => 0, :only_integer => true, :allow_nil => false
+          depth_cache_sql = depth_cache_column
+        end
       else
         # this is not efficient, but it works
         depth_cache_sql = ancestry_depth_sql

test/environment.rb

@@ -126,7 +126,21 @@ def self.with_model options = {}
 
     ActiveRecord::Base.connection.create_table 'test_nodes', **table_options do |table|
       table.send(column_type, options[:ancestry_column], **column_options(force_allow_nil: skip_ancestry))
-      table.integer options[:cache_depth] == true ? :ancestry_depth : options[:cache_depth] if options[:cache_depth]
+      case options[:cache_depth]
+      when true
+        table.integer :ancestry_depth
+      when :virtual
+        # sorry, this duplicates has_ancestry a little
+        ancestry_format = options[:ancestry_format] || Ancestry.default_ancestry_format
+        path_module = ancestry_format == :materialized_path2 ? Ancestry::MaterializedPath2 : Ancestry::MaterializedPath
+        ancestry_depth_sql = path_module.construct_depth_sql("test_nodes", options[:ancestry_column], '/')
+
+        table.virtual :ancestry_depth, type: :integer, as: ancestry_depth_sql, stored: true
+      when nil, false
+        # no column
+      else
+        table.integer options[:cache_depth]
+      end
       if options[:counter_cache]
         counter_cache_column = options[:counter_cache] == true ? :children_count : options[:counter_cache]
         table.integer counter_cache_column, default: 0, null: false