feat: Add dependent: :adopt option for has_closure_tree

README.md

@@ -314,6 +314,7 @@ When you include ```has_closure_tree``` in your model, you can provide a hash to
 * ```:hierarchy_table_name``` to override the hierarchy table name. This defaults to the singular name of the model + "_hierarchies", like ```tag_hierarchies```.
 * ```:dependent``` determines what happens when a node is destroyed. Defaults to ```nullify```.
     * ```:nullify``` will simply set the parent column to null. Each child node will be considered a "root" node. This is the default.
+    * ```:adopt``` will move children to their grandparent (parent's parent). If there is no grandparent, children become root nodes. This is useful for maintaining tree structure when removing intermediate nodes.
     * ```:delete_all``` will delete all descendant nodes (which circumvents the destroy hooks)
     * ```:destroy``` will destroy all descendant nodes (which runs the destroy hooks on each child node)
     * ```nil``` does nothing with descendant nodes

lib/closure_tree/arel_helpers.rb

@@ -79,5 +79,13 @@ def build_hierarchy_delete_query(hierarchy_table, id)
 
       delete_manager
     end
+
+    # Convert an Arel AST to SQL using the correct connection's visitor
+    # This ensures proper quoting for the specific database adapter (MySQL uses backticks, PostgreSQL uses double quotes)
+    def to_sql_with_connection(arel_manager)
+      collector = Arel::Collectors::SQLString.new
+      visitor = connection.send(:arel_visitor)
+      visitor.accept(arel_manager.ast, collector).value
+    end
   end
 end

lib/closure_tree/association_setup.rb

@@ -20,7 +20,7 @@ module AssociationSetup
 
       has_many :children, *_ct.has_many_order_with_option, class_name: _ct.model_class.to_s,
                                                            foreign_key: _ct.parent_column_name,
-                                                           dependent: _ct.options[:dependent],
+                                                           dependent: _ct.options[:dependent] == :adopt ? :nullify : _ct.options[:dependent],
                                                            inverse_of: :parent do
         # We have to redefine hash_tree because the activerecord relation is already scoped to parent_id.
         def hash_tree(options = {})
@@ -47,4 +47,4 @@ def hash_tree(options = {})
                source: :descendant
     end
   end
-end
+end

lib/closure_tree/hierarchy_maintenance.rb

@@ -52,12 +52,26 @@ def _ct_after_save
 
     def _ct_before_destroy
       _ct.with_advisory_lock do
+        adopt_children_to_grandparent if _ct.options[:dependent] == :adopt
         delete_hierarchy_references
         self.class.find(id).children.find_each(&:rebuild!) if _ct.options[:dependent] == :nullify
       end
       true # don't prevent destruction
     end
 
+    def adopt_children_to_grandparent
+      grandparent_id = read_attribute(_ct.parent_column_name)
+      children_ids = self.class.where(_ct.parent_column_name => id).pluck(:id)
+
+      return if children_ids.empty?
+
+      # Update all children's parent_id in a single query
+      self.class.where(id: children_ids).update_all(_ct.parent_column_name => grandparent_id)
+
+      # Rebuild hierarchy for each child
+      self.class.where(id: children_ids).find_each(&:rebuild!)
+    end
+
     def rebuild!(called_by_rebuild = false)
       _ct.with_advisory_lock do
         delete_hierarchy_references unless (defined? @was_new_record) && @was_new_record
@@ -93,7 +107,7 @@ def delete_hierarchy_references
 
         hierarchy_table = hierarchy_class.arel_table
         delete_query = _ct.build_hierarchy_delete_query(hierarchy_table, id)
-        _ct.connection.execute(delete_query.to_sql)
+        _ct.connection.execute(_ct.to_sql_with_connection(delete_query))
       end
     end
 

lib/closure_tree/support.rb

@@ -16,7 +16,7 @@ def initialize(model_class, options)
 
       @options = {
         parent_column_name: 'parent_id',
-        dependent: :nullify, # or :destroy or :delete_all -- see the README
+        dependent: :nullify, # or :destroy, :delete_all, or :adopt -- see the README
         name_column: 'name',
         with_advisory_lock: true, # This will be overridden by adapter support
         numeric_order: false

test/closure_tree/adopt_test.rb

@@ -0,0 +1,270 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+
+def run_adopt_tests_for(model_class)
+  describe "#{model_class} with dependent: :adopt" do
+    before do
+      model_class.delete_all
+      model_class.hierarchy_class.delete_all
+    end
+
+    it 'moves children to grandparent when parent is destroyed and updates hierarchy table' do
+      p1 = model_class.create!(name: 'p1')
+      p2 = model_class.create!(name: 'p2', parent: p1)
+      p3 = model_class.create!(name: 'p3', parent: p2)
+      p4 = model_class.create!(name: 'p4', parent: p3)
+
+      # Verify initial structure: p1 -> p2 -> p3 -> p4
+      assert_equal p2, p3.parent
+      assert_equal p3, p4.parent
+      assert_equal p1, p2.parent
+
+      # Verify initial hierarchy table entries
+      hierarchy = model_class.hierarchy_class
+      assert hierarchy.where(ancestor_id: p1.id, descendant_id: p4.id, generations: 3).exists?
+      assert hierarchy.where(ancestor_id: p2.id, descendant_id: p4.id, generations: 2).exists?
+      assert hierarchy.where(ancestor_id: p3.id, descendant_id: p4.id, generations: 1).exists?
+      assert hierarchy.where(ancestor_id: p3.id, descendant_id: p3.id, generations: 0).exists?
+
+      # Destroy p3
+      p3.destroy
+
+      # After destroying p3, p4 should be adopted by p2 (p3's parent)
+      p4.reload
+      p2.reload
+      assert_equal p2, p4.parent, 'p4 should be moved to p2 (grandparent)'
+      assert_equal p1, p2.parent, 'p2 should still have p1 as parent'
+      assert_equal [p4], p2.children.to_a, 'p2 should have p4 as child'
+
+      # Verify hierarchy table was updated correctly
+      # p3 should be removed from hierarchy
+      assert_empty hierarchy.where(ancestor_id: p3.id)
+      assert_empty hierarchy.where(descendant_id: p3.id)
+
+      # p4 should now have p2 as direct parent (generations: 1)
+      assert hierarchy.where(ancestor_id: p2.id, descendant_id: p4.id, generations: 1).exists?
+      # p4 should have p1 as ancestor (generations: 2)
+      assert hierarchy.where(ancestor_id: p1.id, descendant_id: p4.id, generations: 2).exists?
+      # p4 should have itself (generations: 0)
+      assert hierarchy.where(ancestor_id: p4.id, descendant_id: p4.id, generations: 0).exists?
+    end
+
+    it 'moves children to root when parent without grandparent is destroyed and updates hierarchy table' do
+      p1 = model_class.create!(name: 'p1')
+      p2 = model_class.create!(name: 'p2', parent: p1)
+      p3 = model_class.create!(name: 'p3', parent: p2)
+
+      # Verify initial structure: p1 -> p2 -> p3
+      assert_equal p1, p2.parent
+      assert_equal p2, p3.parent
+
+      hierarchy = model_class.hierarchy_class
+      initial_p2_hierarchies = hierarchy.where(ancestor_id: p2.id).count
+      initial_p3_hierarchies = hierarchy.where(descendant_id: p3.id).count
+
+      # Destroy p1 (root node)
+      p1.destroy
+
+      # After destroying p1, p2 should become root, and p3 should still be child of p2
+      p2.reload
+      p3.reload
+      assert_nil p2.parent, 'p2 should become root'
+      assert_equal p2, p3.parent, 'p3 should still have p2 as parent'
+      assert p2.root?, 'p2 should be a root node'
+      assert_equal [p3], p2.children.to_a, 'p2 should have p3 as child'
+
+      # Verify hierarchy table: p1 should be removed
+      assert_empty hierarchy.where(ancestor_id: p1.id)
+      assert_empty hierarchy.where(descendant_id: p1.id)
+
+      # p2 should now be a root (no ancestors)
+      assert hierarchy.where(ancestor_id: p2.id, descendant_id: p2.id, generations: 0).exists?
+      # p3 should still have p2 as parent
+      assert hierarchy.where(ancestor_id: p2.id, descendant_id: p3.id, generations: 1).exists?
+    end
+
+    it 'handles multiple children being adopted and updates hierarchy table' do
+      p1 = model_class.create!(name: 'p1')
+      p2 = model_class.create!(name: 'p2', parent: p1)
+      c1 = model_class.create!(name: 'c1', parent: p2)
+      c2 = model_class.create!(name: 'c2', parent: p2)
+      c3 = model_class.create!(name: 'c3', parent: p2)
+
+      # Verify initial structure: p1 -> p2 -> [c1, c2, c3]
+      assert_equal [c1, c2, c3].sort, p2.children.to_a.sort
+
+      hierarchy = model_class.hierarchy_class
+      # Verify initial hierarchy: all children should have p1 and p2 as ancestors
+      [c1, c2, c3].each do |child|
+        assert hierarchy.where(ancestor_id: p1.id, descendant_id: child.id, generations: 2).exists?
+        assert hierarchy.where(ancestor_id: p2.id, descendant_id: child.id, generations: 1).exists?
+      end
+
+      # Destroy p2
+      p2.destroy
+
+      # All children should be adopted by p1
+      p1.reload
+      c1.reload
+      c2.reload
+      c3.reload
+
+      assert_equal p1, c1.parent, 'c1 should be moved to p1'
+      assert_equal p1, c2.parent, 'c2 should be moved to p1'
+      assert_equal p1, c3.parent, 'c3 should be moved to p1'
+      assert_equal [c1, c2, c3].sort, p1.children.to_a.sort, 'p1 should have all three children'
+
+      # Verify hierarchy table: p2 should be removed
+      assert_empty hierarchy.where(ancestor_id: p2.id)
+      assert_empty hierarchy.where(descendant_id: p2.id)
+
+      # All children should now have p1 as direct parent (generations: 1)
+      [c1, c2, c3].each do |child|
+        assert hierarchy.where(ancestor_id: p1.id, descendant_id: child.id, generations: 1).exists?
+        # Should not have p2 in their ancestry anymore
+        assert_empty hierarchy.where(ancestor_id: p2.id, descendant_id: child.id)
+      end
+    end
+
+    it 'maintains hierarchy relationships after adoption' do
+      p1 = model_class.create!(name: 'p1')
+      p2 = model_class.create!(name: 'p2', parent: p1)
+      p3 = model_class.create!(name: 'p3', parent: p2)
+      p4 = model_class.create!(name: 'p4', parent: p3)
+      p5 = model_class.create!(name: 'p5', parent: p4)
+
+      # Verify initial structure: p1 -> p2 -> p3 -> p4 -> p5
+      assert_equal %w[p1 p2 p3 p4 p5], p5.ancestry_path
+
+      hierarchy = model_class.hierarchy_class
+      # Verify p5 has all ancestors in hierarchy
+      assert hierarchy.where(ancestor_id: p1.id, descendant_id: p5.id, generations: 4).exists?
+      assert hierarchy.where(ancestor_id: p2.id, descendant_id: p5.id, generations: 3).exists?
+      assert hierarchy.where(ancestor_id: p3.id, descendant_id: p5.id, generations: 2).exists?
+      assert hierarchy.where(ancestor_id: p4.id, descendant_id: p5.id, generations: 1).exists?
+
+      # Destroy p3
+      p3.destroy
+
+      # After adoption, p4 and p5 should still maintain their relationship
+      p4.reload
+      p5.reload
+      assert_equal p2, p4.parent, 'p4 should be adopted by p2'
+      assert_equal p4, p5.parent, 'p5 should still have p4 as parent'
+      assert_equal %w[p1 p2 p4 p5], p5.ancestry_path, 'ancestry path should be updated correctly'
+
+      # Verify hierarchy table: p3 should be removed
+      assert_empty hierarchy.where(ancestor_id: p3.id)
+      assert_empty hierarchy.where(descendant_id: p3.id)
+
+      # p5 should now have p2 as ancestor (generations: 2) and p4 as parent (generations: 1)
+      assert hierarchy.where(ancestor_id: p2.id, descendant_id: p5.id, generations: 2).exists?
+      assert hierarchy.where(ancestor_id: p4.id, descendant_id: p5.id, generations: 1).exists?
+      assert hierarchy.where(ancestor_id: p1.id, descendant_id: p5.id, generations: 3).exists?
+      # p5 should not have p3 in its ancestry anymore
+      assert_empty hierarchy.where(ancestor_id: p3.id, descendant_id: p5.id)
+    end
+
+    it 'handles deep nested structures correctly and updates hierarchy table' do
+      root = model_class.create!(name: 'root')
+      level1 = model_class.create!(name: 'level1', parent: root)
+      level2 = model_class.create!(name: 'level2', parent: level1)
+      level3 = model_class.create!(name: 'level3', parent: level2)
+      level4 = model_class.create!(name: 'level4', parent: level3)
+
+      hierarchy = model_class.hierarchy_class
+      # Verify initial hierarchy for level4
+      assert hierarchy.where(ancestor_id: root.id, descendant_id: level4.id, generations: 4).exists?
+      assert hierarchy.where(ancestor_id: level1.id, descendant_id: level4.id, generations: 3).exists?
+      assert hierarchy.where(ancestor_id: level2.id, descendant_id: level4.id, generations: 2).exists?
+      assert hierarchy.where(ancestor_id: level3.id, descendant_id: level4.id, generations: 1).exists?
+
+      # Destroy level2
+      level2.destroy
+
+      # level3 should be adopted by level1, and level4 should still be child of level3
+      level1.reload
+      level3.reload
+      level4.reload
+
+      assert_equal level1, level3.parent, 'level3 should be adopted by level1'
+      assert_equal level3, level4.parent, 'level4 should still have level3 as parent'
+      assert_equal %w[root level1 level3 level4], level4.ancestry_path
+
+      # Verify hierarchy table: level2 should be removed
+      assert_empty hierarchy.where(ancestor_id: level2.id)
+      assert_empty hierarchy.where(descendant_id: level2.id)
+
+      # level4 should now have correct ancestry without level2
+      assert hierarchy.where(ancestor_id: root.id, descendant_id: level4.id, generations: 3).exists?
+      assert hierarchy.where(ancestor_id: level1.id, descendant_id: level4.id, generations: 2).exists?
+      assert hierarchy.where(ancestor_id: level3.id, descendant_id: level4.id, generations: 1).exists?
+      # level4 should not have level2 in its ancestry anymore
+      assert_empty hierarchy.where(ancestor_id: level2.id, descendant_id: level4.id)
+    end
+
+    it 'handles destroying a node with no children' do
+      p1 = model_class.create!(name: 'p1')
+      p2 = model_class.create!(name: 'p2', parent: p1)
+      leaf = model_class.create!(name: 'leaf', parent: p2)
+
+      hierarchy = model_class.hierarchy_class
+      initial_count = hierarchy.count
+
+      # Destroy leaf (has no children)
+      leaf.destroy
+
+      # Should not raise any errors
+      p1.reload
+      p2.reload
+      assert_equal [p2], p1.children.to_a
+      assert_equal [], p2.children.to_a
+
+      # Hierarchy should be cleaned up
+      assert_empty hierarchy.where(ancestor_id: leaf.id)
+      assert_empty hierarchy.where(descendant_id: leaf.id)
+    end
+
+    it 'works with find_or_create_by_path' do
+      level3 = model_class.find_or_create_by_path(%w[root level1 level2 level3])
+      root = level3.root
+      level1 = root.children.find_by(name: 'level1')
+      level2 = level1.children.find_by(name: 'level2')
+
+      hierarchy = model_class.hierarchy_class
+      # Verify initial hierarchy
+      assert hierarchy.where(ancestor_id: root.id, descendant_id: level3.id).exists?
+      assert hierarchy.where(ancestor_id: level2.id, descendant_id: level3.id, generations: 1).exists?
+
+      # Destroy level2
+      level2.destroy
+
+      # level3 should be adopted by level1
+      level1.reload
+      level3.reload
+      assert_equal level1, level3.parent
+      assert_equal %w[root level1 level3], level3.ancestry_path
+
+      # Verify hierarchy table
+      assert_empty hierarchy.where(ancestor_id: level2.id)
+      assert hierarchy.where(ancestor_id: level1.id, descendant_id: level3.id, generations: 1).exists?
+      assert hierarchy.where(ancestor_id: root.id, descendant_id: level3.id, generations: 2).exists?
+    end
+  end
+end
+
+# Test with PostgreSQL
+if postgresql?(ApplicationRecord.connection)
+  run_adopt_tests_for(AdoptableTag)
+end
+
+# Test with MySQL
+if mysql?(MysqlRecord.connection)
+  run_adopt_tests_for(MysqlAdoptableTag)
+end
+
+# Test with SQLite
+if sqlite?(SqliteRecord.connection)
+  run_adopt_tests_for(MemoryAdoptableTag)
+end

test/dummy/app/models/adoptable_tag.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class AdoptableTag < ApplicationRecord
+  has_closure_tree dependent: :adopt, name_column: 'name'
+end
+
+

test/dummy/app/models/memory_adoptable_tag.rb

@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+class MemoryAdoptableTag < SqliteRecord
+  has_closure_tree dependent: :adopt, name_column: 'name'
+end
+

test/dummy/app/models/mysql_adoptable_tag.rb

@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+class MysqlAdoptableTag < MysqlRecord
+  has_closure_tree dependent: :adopt, name_column: 'name'
+end
+