Implement depth as a subquery

The main reason I introduced depth sql is to improve rebuild_depth_cache_sql!
Throwing this into the scopes is a bonus. (but not really)

This works great for the update, but the extra scopes will not perform well.
If you need to use them, consider adding an index on that equation

lib/ancestry/class_methods.rb

@@ -225,6 +225,10 @@ def rebuild_depth_cache!
       end
     end
 
+    def rebuild_depth_cache_sql!
+      update_all("#{depth_cache_column} = #{ancestry_depth_sql}")
+    end
+
     def unscoped_where
       yield ancestry_base_class.default_scoped.unscope(:where)
     end

lib/ancestry/has_ancestry.rb

@@ -103,7 +103,12 @@ def has_ancestry options = {}
         scope :from_depth,   lambda { |depth| where("#{depth_cache_column} >= ?", depth) }
         scope :after_depth,  lambda { |depth| where("#{depth_cache_column} > ?", depth) }
       else
-        # TODO: pure sql implementation of these scopse around depth_sql (from strategy)
+        # this is not efficient, but it works
+        scope :before_depth, lambda { |depth| where("#{ancestry_depth_sql} < ?", depth) }
+        scope :to_depth,     lambda { |depth| where("#{ancestry_depth_sql} <= ?", depth) }
+        scope :at_depth,     lambda { |depth| where("#{ancestry_depth_sql} = ?", depth) }
+        scope :from_depth,   lambda { |depth| where("#{ancestry_depth_sql} >= ?", depth) }
+        scope :after_depth,  lambda { |depth| where("#{ancestry_depth_sql} > ?", depth) }
       end
 
       # Create counter cache column accessor and set to option or default

lib/ancestry/materialized_path.rb

@@ -92,6 +92,15 @@ def ancestry_root
       nil
     end
 
+    def ancestry_depth_sql
+      @ancestry_depth_sql ||=
+        begin
+          tmp = %{(LENGTH(#{table_name}.#{ancestry_column}) - LENGTH(REPLACE(#{table_name}.#{ancestry_column},'#{ancestry_delimiter}','')))}
+          tmp = tmp + "/#{ancestry_delimiter.size}" if ancestry_delimiter.size > 1
+          "(CASE WHEN #{table_name}.#{ancestry_column} IS NULL THEN 0 ELSE 1 + #{tmp} END)"
+        end
+    end
+
     private
 
     def ancestry_validation_options(ancestry_primary_key_format)

lib/ancestry/materialized_path2.rb

@@ -28,6 +28,15 @@ def ancestry_root
       ancestry_delimiter
     end
 
+    def ancestry_depth_sql
+      @ancestry_depth_sql ||=
+        begin
+          tmp = %{(LENGTH(#{table_name}.#{ancestry_column}) - LENGTH(REPLACE(#{table_name}.#{ancestry_column},'#{ancestry_delimiter}','')))}
+          tmp = tmp + "/#{ancestry_delimiter.size}" if ancestry_delimiter.size > 1
+          "(#{tmp} -1)"
+        end
+    end
+
     private
 
     def ancestry_nil_allowed?

test/concerns/depth_caching_test.rb

@@ -36,19 +36,19 @@ def test_depth_scopes
     end
   end
 
-  def test_depth_scopes_unavailable
-    AncestryTestDatabase.with_model do |model|
-      refute model.respond_to?(:before_depth)
-      refute model.respond_to?(:to_depth)
-      refute model.respond_to?(:at_depth)
-      refute model.respond_to?(:from_depth)
-      refute model.respond_to?(:after_depth)
+  def test_depth_scopes_without_depth_cache
+    AncestryTestDatabase.with_model :depth => 4, :width => 2 do |model, _roots|
+      model.before_depth(2).all? { |node| assert node.depth < 2 }
+      model.to_depth(2).all?     { |node| assert node.depth <= 2 }
+      model.at_depth(2).all?     { |node| assert node.depth == 2 }
+      model.from_depth(2).all?   { |node| assert node.depth >= 2 }
+      model.after_depth(2).all?  { |node| assert node.depth > 2 }
     end
   end
 
   def test_rebuild_depth_cache
     AncestryTestDatabase.with_model :depth => 3, :width => 3, :cache_depth => :depth_cache do |model, _roots|
-      model.connection.execute("update test_nodes set depth_cache = null;")
+      model.update_all(:depth_cache => nil)
 
       # Assert cache was emptied correctly
       model.all.each do |test_node|
@@ -65,6 +65,27 @@ def test_rebuild_depth_cache
     end
   end
 
+  def test_rebuild_depth_cache_with_sql
+    AncestryTestDatabase.with_model :depth => 3, :width => 3, :cache_depth => :depth_cache do |model, _roots|
+      model.update_all(:depth_cache => nil)
+
+      # Assert cache was emptied correctly
+      model.all.each do |test_node|
+        assert_nil test_node.depth_cache
+      end
+
+      # Rebuild cache
+      # require "byebug"
+      # byebug
+      model.rebuild_depth_cache_sql!
+
+      # Assert cache was rebuild correctly
+      model.all.each do |test_node|
+        assert_equal test_node.depth, test_node.depth_cache
+      end
+    end
+  end
+
   def test_exception_when_rebuilding_depth_cache_for_model_without_depth_caching
     AncestryTestDatabase.with_model do |model|
       assert_raise Ancestry::AncestryException do
@@ -80,4 +101,4 @@ def test_exception_on_unknown_depth_column
       end
     end
   end
-end
+end