Validate hierarchies

app/models/org_unit.rb

@@ -9,15 +9,15 @@ class OrgUnit < ApplicationRecord
              class_name: 'OrgUnitKind',
              inverse_of: :instances
 
-  belongs_to :parent,
+  belongs_to :parent_unit,
              class_name: 'OrgUnit',
-             inverse_of: :children,
+             inverse_of: :children_units,
              optional: true
 
-  has_many :children,
+  has_many :children_units,
            class_name: 'OrgUnit',
-           inverse_of: :parent,
-           foreign_key: :parent_id
+           inverse_of: :parent_unit,
+           foreign_key: :parent_unit_id
 
   has_many :all_relationships,
            class_name: 'Relationship',
@@ -31,7 +31,7 @@ class OrgUnit < ApplicationRecord
 
   validates :name, good_small_text: true, uniqueness: true
 
-  validates :parent,
+  validates :parent_unit,
             presence: {
               if: ->(record) { record.kind&.parent_kind },
               message: :required,
@@ -39,9 +39,19 @@ class OrgUnit < ApplicationRecord
 
   validate :parent_matches_kind
 
+  #############
+  # Callbacks #
+  #############
+
+  before_validation :set_level
+
 private
 
   def parent_matches_kind
-    errors.add :parent unless parent&.kind == kind&.parent_kind
+    errors.add :parent_unit unless parent_unit&.kind == kind&.parent_kind
+  end
+
+  def set_level
+    self.level = parent_unit.nil? ? 0 : parent_unit.level + 1
   end
 end

app/models/org_unit_kind.rb

@@ -30,6 +30,12 @@ class OrgUnitKind < ApplicationRecord
 
   validates :name, good_small_text: true, uniqueness: true
 
+  #############
+  # Callbacks #
+  #############
+
+  before_validation :set_level
+
   ###########
   # Methods #
   ###########
@@ -37,4 +43,10 @@ class OrgUnitKind < ApplicationRecord
   def to_param
     codename
   end
+
+private
+
+  def set_level
+    self.level = parent_kind.nil? ? 0 : parent_kind.level + 1
+  end
 end

app/models/relationship.rb

@@ -7,13 +7,35 @@ class Relationship < ApplicationRecord
 
   belongs_to :org_unit, inverse_of: :all_relationships
 
+  belongs_to :parent_rel,
+             class_name: 'Relationship',
+             inverse_of: :children_rels,
+             optional: true
+
   belongs_to :status, class_name: 'RelationStatus'
 
   belongs_to :person, inverse_of: :all_relationships
 
+  has_many :children_rels,
+           class_name: 'Relationship',
+           inverse_of: :parent_rel,
+           foreign_key: :parent_rel_id
+
   ###############
   # Validations #
   ###############
 
   validates :from_date, presence: true, uniqueness: { scope: :person_id }
+
+  #############
+  # Callbacks #
+  #############
+
+  before_validation :set_level
+
+private
+
+  def set_level
+    self.level = parent_rel.nil? ? 0 : parent_rel.level + 1
+  end
 end

app/views/staffs/org_units/show.html.erb

@@ -24,15 +24,15 @@
     <dt><%= OrgUnit.human_attribute_name :name %></dt>
     <dd><%= @org_unit.name %></dd>
 
-    <dt><%= OrgUnit.human_attribute_name :parent %></dt>
+    <dt><%= OrgUnit.human_attribute_name :parent_unit %></dt>
     <dd>
-      <% if @org_unit.parent.nil? %>
+      <% if @org_unit.parent_unit.nil? %>
         <%= none %>
-      <% elsif policy([:staff, @org_unit.parent]).show? %>
-        <%= link_to @org_unit.parent.name,
-                    [:staff, @org_unit.parent] %>
+      <% elsif policy([:staff, @org_unit.parent_unit]).show? %>
+        <%= link_to @org_unit.parent_unit.name,
+                    [:staff, @org_unit.parent_unit] %>
       <% else %>
-        <%= @org_unit.parent.name %>
+        <%= @org_unit.parent_unit.name %>
       <% end %>
     </dd>
   </dl>

config/locales/activerecord/en.yml

@@ -77,7 +77,7 @@ en:
         kind: Type
         short_name: Short name
         name: Name
-        parent: Parent
+        parent_unit: Parent
       org_unit_kind:
         id: ID
         codename: Codename

config/locales/activerecord/ru.yml

@@ -77,7 +77,7 @@ ru:
         kind: Тип
         short_name: Короткое развание
         name: Название
-        parent: Родитель
+        parent_unit: Родитель
       org_unit_kind:
         id: ID
         codename: Кодовое имя

db/migrate/20191002002101_add_level_to_tables.rb

@@ -0,0 +1,229 @@
+# frozen_string_literal: true
+
+class AddLevelToTables < ActiveRecord::Migration[6.0]
+  include Partynest::Migration
+
+  def change
+    rename_column :org_units, :parent_id, :parent_unit_id
+
+    add_reference :relationships,
+                  :parent_rel,
+                  null: true,
+                  index: true,
+                  foreign_key: { to_table: :relationships }
+
+    # rubocop:disable Rails/NotNullColumn
+    add_column :org_unit_kinds, :level, :integer, null: false
+    add_column :org_units,      :level, :integer, null: false
+    add_column :relationships,  :level, :integer, null: false
+    # rubocop:enable Rails/NotNullColumn
+
+    add_constraint :org_unit_kinds, :level, 'level >= 0'
+    add_constraint :org_units,      :level, 'level >= 0'
+    add_constraint :relationships,  :level, 'level >= 0'
+
+    add_constraint :org_unit_kinds, :parent_kind, 'parent_kind_id != id'
+    add_constraint :org_units,      :parent_unit, 'parent_unit_id != id'
+    add_constraint :relationships,  :parent_rel,  'parent_rel_id  != id'
+
+    add_func_validate_org_unit_kind_hierarchy
+    add_func_validate_org_unit_hierarchy
+    add_func_validate_relationship_hierarchy
+
+    add_trigger :org_unit_kinds,
+                :validate_hierarchy,
+                'BEFORE INSERT OR UPDATE',
+                'validate_org_unit_kind_hierarchy()'
+
+    add_trigger :org_units,
+                :validate_hierarchy,
+                'BEFORE INSERT OR UPDATE',
+                'validate_org_unit_hierarchy()'
+
+    add_trigger :relationships,
+                :validate_hierarchy,
+                'BEFORE INSERT OR UPDATE',
+                'validate_relationship_hierarchy()'
+  end
+
+  def add_func_validate_org_unit_kind_hierarchy
+    add_func :validate_org_unit_kind_hierarchy, <<~SQL
+      () RETURNS trigger LANGUAGE plpgsql AS
+      $$
+      DECLARE
+        parent_kind record;
+      BEGIN
+        IF NEW.parent_kind_id IS NULL THEN
+          IF NEW.level != 0 THEN
+            RAISE EXCEPTION 'level is invalid';
+          END IF;
+
+          RETURN NEW;
+        END IF;
+
+        SELECT *
+          FROM org_unit_kinds
+          INTO parent_kind
+          WHERE id = NEW.parent_kind_id;
+
+        IF parent_kind IS NULL THEN
+          RAISE EXCEPTION 'can not find parent';
+        END IF;
+
+        IF NEW.level != parent_kind.level + 1 THEN
+          RAISE EXCEPTION 'level is invalid';
+        END IF;
+
+        RETURN NEW;
+      END;
+      $$;
+    SQL
+  end
+
+  def add_func_validate_org_unit_hierarchy
+    add_func :validate_org_unit_hierarchy, <<~SQL
+      () RETURNS trigger LANGUAGE plpgsql AS
+      $$
+      DECLARE
+        kind record;
+        parent_kind record;
+        parent_unit record;
+      BEGIN
+        IF NEW.kind_id IS NULL THEN
+          RAISE EXCEPTION 'does not have type';
+        END IF;
+
+        SELECT *
+          FROM org_unit_kinds
+          INTO kind
+          WHERE id = NEW.kind_id;
+
+        IF kind IS NULL THEN
+          RAISE EXCEPTION 'can not find type';
+        END IF;
+
+        SELECT *
+          FROM org_unit_kinds
+          INTO parent_kind
+          WHERE id = kind.parent_kind_id;
+
+        IF (kind.parent_kind_id IS NULL) != (parent_kind IS NULL) THEN
+          RAISE EXCEPTION 'can not find parent type';
+        END IF;
+
+        IF parent_kind IS NULL THEN
+          IF NEW.parent_unit_id IS NOT NULL THEN
+            RAISE EXCEPTION 'parent is invalid (expected NULL)';
+          END IF;
+
+          IF NEW.level != 0 THEN
+            RAISE EXCEPTION 'level is invalid';
+          END IF;
+
+          RETURN NEW;
+        END IF;
+
+        IF NEW.parent_unit_id IS NULL THEN
+          RAISE EXCEPTION 'parent is invalid (expected NOT NULL)';
+        END IF;
+
+        SELECT *
+          FROM org_units
+          INTO parent_unit
+          WHERE id = NEW.parent_unit_id;
+
+        IF parent_unit IS NULL THEN
+          RAISE EXCEPTION 'can not find parent';
+        END IF;
+
+        IF parent_unit.kind_id != parent_kind.id THEN
+          RAISE EXCEPTION 'parent is invalid';
+        END IF;
+
+        IF (
+          NEW.level != kind.level            OR
+          NEW.level != parent_kind.level + 1 OR
+          NEW.level != parent_unit.level + 1
+        ) THEN
+          RAISE EXCEPTION 'level is invalid';
+        END IF;
+
+        RETURN NEW;
+      END;
+      $$;
+    SQL
+  end
+
+  def add_func_validate_relationship_hierarchy
+    add_func :validate_relationship_hierarchy, <<~SQL
+      () RETURNS trigger LANGUAGE plpgsql AS
+      $$
+      DECLARE
+        org_unit record;
+        parent_unit record;
+        parent_rel record;
+      BEGIN
+        IF NEW.org_unit_id IS NULL THEN
+          RAISE EXCEPTION 'does not have org unit';
+        END IF;
+
+        SELECT *
+          FROM org_units
+          INTO org_unit
+          WHERE id = NEW.org_unit_id;
+
+        IF org_unit IS NULL THEN
+          RAISE EXCEPTION 'can not find org unit';
+        END IF;
+
+        SELECT *
+          FROM org_units
+          INTO parent_unit
+          WHERE id = org_unit.parent_unit_id;
+
+        IF (org_unit.parent_unit_id IS NULL) != (parent_unit IS NULL) THEN
+          RAISE EXCEPTION 'can not find parent org unit';
+        END IF;
+
+        IF parent_unit IS NULL THEN
+          IF NEW.parent_rel_id IS NOT NULL THEN
+            RAISE EXCEPTION 'parent rel is invalid (expected NULL)';
+          END IF;
+
+          IF NEW.level != 0 THEN
+            RAISE EXCEPTION 'level is invalid (expected 0)';
+          END IF;
+
+          RETURN NEW;
+        END IF;
+
+        IF NEW.parent_rel_id IS NULL THEN
+          RAISE EXCEPTION 'parent rel is invalid (expected NOT NULL)';
+        END IF;
+
+        SELECT *
+          FROM relationships
+          INTO parent_rel
+          WHERE id = NEW.parent_rel_id;
+
+        IF parent_rel IS NULL THEN
+          RAISE EXCEPTION 'can not find parent rel';
+        END IF;
+
+        IF parent_rel.org_unit_id != parent_unit.id THEN
+          RAISE EXCEPTION 'parent rel is invalid';
+        END IF;
+
+        IF (
+          NEW.level != org_unit.level        OR
+          NEW.level != parent_unit.level + 1 OR
+          NEW.level != parent_rel.level  + 1
+        ) THEN
+        END IF;
+
+        RETURN NEW;
+      END;
+      $$;
+    SQL
+  end
+end

db/structure.sql

@@ -199,6 +199,193 @@ END;
 $_$;
 
 
+--
+-- Name: validate_org_unit_hierarchy(); Type: FUNCTION; Schema: public; Owner: -
+--
+
+CREATE FUNCTION public.validate_org_unit_hierarchy() RETURNS trigger
+    LANGUAGE plpgsql
+    AS $$
+DECLARE
+  kind record;
+  parent_kind record;
+  parent_unit record;
+BEGIN
+  IF NEW.kind_id IS NULL THEN
+    RAISE EXCEPTION 'does not have type';
+  END IF;
+
+  SELECT *
+    FROM org_unit_kinds
+    INTO kind
+    WHERE id = NEW.kind_id;
+
+  IF kind IS NULL THEN
+    RAISE EXCEPTION 'can not find type';
+  END IF;
+
+  SELECT *
+    FROM org_unit_kinds
+    INTO parent_kind
+    WHERE id = kind.parent_kind_id;
+
+  IF (kind.parent_kind_id IS NULL) != (parent_kind IS NULL) THEN
+    RAISE EXCEPTION 'can not find parent type';
+  END IF;
+
+  IF parent_kind IS NULL THEN
+    IF NEW.parent_unit_id IS NOT NULL THEN
+      RAISE EXCEPTION 'parent is invalid (expected NULL)';
+    END IF;
+
+    IF NEW.level != 0 THEN
+      RAISE EXCEPTION 'level is invalid';
+    END IF;
+
+    RETURN NEW;
+  END IF;
+
+  IF NEW.parent_unit_id IS NULL THEN
+    RAISE EXCEPTION 'parent is invalid (expected NOT NULL)';
+  END IF;
+
+  SELECT *
+    FROM org_units
+    INTO parent_unit
+    WHERE id = NEW.parent_unit_id;
+
+  IF parent_unit IS NULL THEN
+    RAISE EXCEPTION 'can not find parent';
+  END IF;
+
+  IF parent_unit.kind_id != parent_kind.id THEN
+    RAISE EXCEPTION 'parent is invalid';
+  END IF;
+
+  IF (
+    NEW.level != kind.level            OR
+    NEW.level != parent_kind.level + 1 OR
+    NEW.level != parent_unit.level + 1
+  ) THEN
+    RAISE EXCEPTION 'level is invalid';
+  END IF;
+
+  RETURN NEW;
+END;
+$$;
+
+
+--
+-- Name: validate_org_unit_kind_hierarchy(); Type: FUNCTION; Schema: public; Owner: -
+--
+
+CREATE FUNCTION public.validate_org_unit_kind_hierarchy() RETURNS trigger
+    LANGUAGE plpgsql
+    AS $$
+DECLARE
+  parent_kind record;
+BEGIN
+  IF NEW.parent_kind_id IS NULL THEN
+    IF NEW.level != 0 THEN
+      RAISE EXCEPTION 'level is invalid';
+    END IF;
+
+    RETURN NEW;
+  END IF;
+
+  SELECT *
+    FROM org_unit_kinds
+    INTO parent_kind
+    WHERE id = NEW.parent_kind_id;
+
+  IF parent_kind IS NULL THEN
+    RAISE EXCEPTION 'can not find parent';
+  END IF;
+
+  IF NEW.level != parent_kind.level + 1 THEN
+    RAISE EXCEPTION 'level is invalid';
+  END IF;
+
+  RETURN NEW;
+END;
+$$;
+
+
+--
+-- Name: validate_relationship_hierarchy(); Type: FUNCTION; Schema: public; Owner: -
+--
+
+CREATE FUNCTION public.validate_relationship_hierarchy() RETURNS trigger
+    LANGUAGE plpgsql
+    AS $$
+DECLARE
+  org_unit record;
+  parent_unit record;
+  parent_rel record;
+BEGIN
+  IF NEW.org_unit_id IS NULL THEN
+    RAISE EXCEPTION 'does not have org unit';
+  END IF;
+
+  SELECT *
+    FROM org_units
+    INTO org_unit
+    WHERE id = NEW.org_unit_id;
+
+  IF org_unit IS NULL THEN
+    RAISE EXCEPTION 'can not find org unit';
+  END IF;
+
+  SELECT *
+    FROM org_units
+    INTO parent_unit
+    WHERE id = org_unit.parent_unit_id;
+
+  IF (org_unit.parent_unit_id IS NULL) != (parent_unit IS NULL) THEN
+    RAISE EXCEPTION 'can not find parent org unit';
+  END IF;
+
+  IF parent_unit IS NULL THEN
+    IF NEW.parent_rel_id IS NOT NULL THEN
+      RAISE EXCEPTION 'parent rel is invalid (expected NULL)';
+    END IF;
+
+    IF NEW.level != 0 THEN
+      RAISE EXCEPTION 'level is invalid (expected 0)';
+    END IF;
+
+    RETURN NEW;
+  END IF;
+
+  IF NEW.parent_rel_id IS NULL THEN
+    RAISE EXCEPTION 'parent rel is invalid (expected NOT NULL)';
+  END IF;
+
+  SELECT *
+    FROM relationships
+    INTO parent_rel
+    WHERE id = NEW.parent_rel_id;
+
+  IF parent_rel IS NULL THEN
+    RAISE EXCEPTION 'can not find parent rel';
+  END IF;
+
+  IF parent_rel.org_unit_id != parent_unit.id THEN
+    RAISE EXCEPTION 'parent rel is invalid';
+  END IF;
+
+  IF (
+    NEW.level != org_unit.level        OR
+    NEW.level != parent_unit.level + 1 OR
+    NEW.level != parent_rel.level  + 1
+  ) THEN
+  END IF;
+
+  RETURN NEW;
+END;
+$$;
+
+
 SET default_tablespace = '';
 
 SET default_with_oids = false;
@@ -473,8 +660,11 @@ CREATE TABLE public.org_unit_kinds (
     short_name character varying NOT NULL,
     name character varying NOT NULL,
     parent_kind_id bigint,
+    level integer NOT NULL,
     CONSTRAINT codename CHECK (public.is_codename((codename)::text)),
+    CONSTRAINT level CHECK ((level >= 0)),
     CONSTRAINT name CHECK (public.is_good_small_text((name)::text)),
+    CONSTRAINT parent_kind CHECK ((parent_kind_id <> id)),
     CONSTRAINT short_name CHECK (public.is_good_small_text((short_name)::text))
 );
 
@@ -509,8 +699,11 @@ CREATE TABLE public.org_units (
     short_name character varying NOT NULL,
     name character varying NOT NULL,
     kind_id bigint NOT NULL,
-    parent_id bigint,
+    parent_unit_id bigint,
+    level integer NOT NULL,
+    CONSTRAINT level CHECK ((level >= 0)),
     CONSTRAINT name CHECK (public.is_good_small_text((name)::text)),
+    CONSTRAINT parent_unit CHECK ((parent_unit_id <> id)),
     CONSTRAINT short_name CHECK (public.is_good_small_text((short_name)::text))
 );
 
@@ -759,7 +952,11 @@ CREATE TABLE public.relationships (
     person_id bigint NOT NULL,
     from_date date NOT NULL,
     status_id bigint NOT NULL,
-    org_unit_id bigint NOT NULL
+    org_unit_id bigint NOT NULL,
+    parent_rel_id bigint,
+    level integer NOT NULL,
+    CONSTRAINT level CHECK ((level >= 0)),
+    CONSTRAINT parent_rel CHECK ((parent_rel_id <> id))
 );
 
 
@@ -1343,10 +1540,10 @@ CREATE UNIQUE INDEX index_org_units_on_name ON public.org_units USING btree (nam
 
 
 --
--- Name: index_org_units_on_parent_id; Type: INDEX; Schema: public; Owner: -
+-- Name: index_org_units_on_parent_unit_id; Type: INDEX; Schema: public; Owner: -
 --
 
-CREATE INDEX index_org_units_on_parent_id ON public.org_units USING btree (parent_id);
+CREATE INDEX index_org_units_on_parent_unit_id ON public.org_units USING btree (parent_unit_id);
 
 
 --
@@ -1454,6 +1651,13 @@ CREATE INDEX index_relationships_on_from_date ON public.relationships USING btre
 CREATE INDEX index_relationships_on_org_unit_id ON public.relationships USING btree (org_unit_id);
 
 
+--
+-- Name: index_relationships_on_parent_rel_id; Type: INDEX; Schema: public; Owner: -
+--
+
+CREATE INDEX index_relationships_on_parent_rel_id ON public.relationships USING btree (parent_rel_id);
+
+
 --
 -- Name: index_relationships_on_person_id_and_from_date; Type: INDEX; Schema: public; Owner: -
 --
@@ -1545,6 +1749,27 @@ CREATE TRIGGER ensure_contact_list_id_remains_unchanged BEFORE UPDATE OF contact
 CREATE TRIGGER ensure_superuser_has_related_user BEFORE INSERT OR UPDATE ON public.accounts FOR EACH ROW EXECUTE PROCEDURE public.ensure_superuser_has_related_user();
 
 
+--
+-- Name: org_unit_kinds validate_hierarchy; Type: TRIGGER; Schema: public; Owner: -
+--
+
+CREATE TRIGGER validate_hierarchy BEFORE INSERT OR UPDATE ON public.org_unit_kinds FOR EACH ROW EXECUTE PROCEDURE public.validate_org_unit_kind_hierarchy();
+
+
+--
+-- Name: org_units validate_hierarchy; Type: TRIGGER; Schema: public; Owner: -
+--
+
+CREATE TRIGGER validate_hierarchy BEFORE INSERT OR UPDATE ON public.org_units FOR EACH ROW EXECUTE PROCEDURE public.validate_org_unit_hierarchy();
+
+
+--
+-- Name: relationships validate_hierarchy; Type: TRIGGER; Schema: public; Owner: -
+--
+
+CREATE TRIGGER validate_hierarchy BEFORE INSERT OR UPDATE ON public.relationships FOR EACH ROW EXECUTE PROCEDURE public.validate_relationship_hierarchy();
+
+
 --
 -- Name: relationships fk_rails_0ea63a126c; Type: FK CONSTRAINT; Schema: public; Owner: -
 --
@@ -1566,7 +1791,7 @@ ALTER TABLE ONLY public.people
 --
 
 ALTER TABLE ONLY public.org_units
-    ADD CONSTRAINT fk_rails_54c0512b74 FOREIGN KEY (parent_id) REFERENCES public.org_units(id);
+    ADD CONSTRAINT fk_rails_54c0512b74 FOREIGN KEY (parent_unit_id) REFERENCES public.org_units(id);
 
 
 --
@@ -1657,6 +1882,14 @@ ALTER TABLE ONLY public.relation_transitions
     ADD CONSTRAINT fk_rails_b61956945e FOREIGN KEY (from_status_id) REFERENCES public.relation_statuses(id);
 
 
+--
+-- Name: relationships fk_rails_b943fd3c34; Type: FK CONSTRAINT; Schema: public; Owner: -
+--
+
+ALTER TABLE ONLY public.relationships
+    ADD CONSTRAINT fk_rails_b943fd3c34 FOREIGN KEY (parent_rel_id) REFERENCES public.relationships(id);
+
+
 --
 -- Name: org_units fk_rails_ccc56f184e; Type: FK CONSTRAINT; Schema: public; Owner: -
 --
@@ -1725,6 +1958,7 @@ INSERT INTO "schema_migrations" (version) VALUES
 ('20190930210852'),
 ('20190930215223'),
 ('20191001022049'),
-('20191001211809');
+('20191001211809'),
+('20191002002101');
 
 

factories/org_units.rb

@@ -10,7 +10,7 @@ FactoryBot.define do
     trait :with_parent do
       association :kind, factory: :some_children_org_unit_kind
 
-      parent { create :some_root_org_unit, kind: kind.parent_kind }
+      parent_unit { create :some_root_org_unit, kind: kind.parent_kind }
     end
   end
 

factories/relationships.rb

@@ -1,16 +1,30 @@
 # frozen_string_literal: true
 
 FactoryBot.define do
-  factory :supporter_relationship, class: Relationship do
-    association :org_unit, factory: :some_children_org_unit
+  factory :some_root_relationship, class: Relationship do
+    association :org_unit, factory: :some_root_org_unit
     association :status, factory: :some_relation_status
     association :person, factory: :initial_person
 
     sequence :from_date do |n|
       Date.new rand((10 * n)...(11 * n)), rand(1..12), rand(1..28)
     end
+
+    trait :with_parent do
+      association :org_unit, factory: :some_children_org_unit
+
+      parent_rel do
+        create :some_root_relationship, org_unit: org_unit&.parent_unit
+      end
+    end
   end
 
+  factory :some_children_relationship,
+          parent: :some_root_relationship,
+          traits: %i[with_parent]
+
+  factory :supporter_relationship, parent: :some_children_relationship
+
   factory :excluded_relationship, parent: :supporter_relationship
 
   factory :member_relationship, parent: :supporter_relationship

lib/partynest/migration.rb

@@ -44,6 +44,20 @@ module Partynest
       end
     end
 
+    def add_trigger(table, name, events, call)
+      reversible do |dir|
+        dir.up   { trigger_creation(table, name, events, call).call }
+        dir.down { trigger_deletion(table, name).call               }
+      end
+    end
+
+    def remove_trigger(table, name, events, call)
+      reversible do |dir|
+        dir.up   { trigger_deletion(table, name).call               }
+        dir.down { trigger_creation(table, name, events, call).call }
+      end
+    end
+
   private
 
     def func_creation(name, sql)
@@ -69,6 +83,18 @@ module Partynest
       end
     end
 
+    def trigger_creation(table, name, events, call)
+      lambda do
+        execute <<~SQL
+          CREATE TRIGGER #{name}
+            #{events}
+            ON #{table}
+            FOR EACH ROW
+            EXECUTE PROCEDURE #{call};
+        SQL
+      end
+    end
+
     def func_deletion(name)
       lambda do
         execute "DROP FUNCTION #{name}"
@@ -86,5 +112,11 @@ module Partynest
         execute "ALTER TABLE #{table} DROP CONSTRAINT #{name}"
       end
     end
+
+    def trigger_deletion(table, name)
+      lambda do
+        execute "DROP TRIGGER #{name} ON #{table}"
+      end
+    end
   end
 end

spec/models/org_unit_spec.rb

@@ -17,19 +17,21 @@ RSpec.describe OrgUnit do
     it { is_expected.to validate_presence_of(:kind).with_message(:required) }
   end
 
-  describe '#parent' do
+  describe '#parent_unit' do
     it do
       is_expected.to \
-        belong_to(:parent)
+        belong_to(:parent_unit)
         .class_name('OrgUnit')
-        .inverse_of(:children)
+        .inverse_of(:children_units)
     end
 
     context 'when organizational unit type does not require parent' do
       subject { create :some_root_org_unit }
 
       it do
-        is_expected.not_to validate_presence_of(:parent).with_message(:required)
+        is_expected.not_to \
+          validate_presence_of(:parent_unit)
+          .with_message(:required)
       end
     end
 
@@ -37,18 +39,20 @@ RSpec.describe OrgUnit do
       subject { create :some_children_org_unit }
 
       it do
-        is_expected.to validate_presence_of(:parent).with_message(:required)
+        is_expected.to \
+          validate_presence_of(:parent_unit)
+          .with_message(:required)
       end
     end
   end
 
-  describe '#children' do
+  describe '#children_units' do
     it do
       is_expected.to \
-        have_many(:children)
+        have_many(:children_units)
         .class_name('OrgUnit')
-        .inverse_of(:parent)
-        .with_foreign_key(:parent_id)
+        .inverse_of(:parent_unit)
+        .with_foreign_key(:parent_unit_id)
         .dependent(:restrict_with_exception)
     end
   end

spec/models/relationship_spec.rb

@@ -14,6 +14,27 @@ RSpec.describe Relationship do
     end
   end
 
+  describe '#parent_rel' do
+    it do
+      is_expected.to \
+        belong_to(:parent_rel)
+        .class_name('Relationship')
+        .inverse_of(:children_rels)
+        .optional
+    end
+  end
+
+  describe '#children_rels' do
+    it do
+      is_expected.to \
+        have_many(:children_rels)
+        .class_name('Relationship')
+        .inverse_of(:parent_rel)
+        .with_foreign_key(:parent_rel_id)
+        .dependent(:restrict_with_exception)
+    end
+  end
+
   describe '#status' do
     it do
       is_expected.to belong_to(:status).class_name('RelationStatus').required