Municipalities with many areas

Data structure to save Japanese municipalities and the associated areas.

app/models/municipality.rb

@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+
+class Municipality < ApplicationRecord
+  has_many :municipality_areas, dependent: :destroy
+end

app/models/municipality_area.rb

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+# frozen_string_literal: true
+
+class MunicipalityArea < ApplicationRecord
+  belongs_to :municipality
+end

db/migrate/20230214152809_create_municipalities.rb

@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+class CreateMunicipalities < ActiveRecord::Migration[7.0]
+  def change
+    create_table :municipalities do |t|
+      t.string :name, null: false
+    end
+  end
+end

db/migrate/20230214160225_create_municipality_areas.rb

@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+class CreateMunicipalityAreas < ActiveRecord::Migration[7.0]
+  def change
+    create_table :municipality_areas do |t|
+      t.references :municipality, null: false, foreign_key: true
+      t.st_polygon :area, null: false, srid: 3857, index: { using: :gist }
+    end
+  end
+end