Dependency graph of Postgres tables based on FK constraints

rails_fk_dependency_graph.rb

# Provides a dependency graph of PG tables based on FK constraints,
# in the form of a hash map:
#   {
#     "some_table" => ["dependent_table_1", "dependent_table_2"],
#     "dependent_table_1"=> ["dependent_table_3"],
#     # ...
#   }
def fk_dependency_graph
  query = <<~SQL
    SELECT
      ccu.table_name AS main_table,
      tc.table_name AS dependent_table
    FROM
      information_schema.table_constraints AS tc
      JOIN information_schema.key_column_usage AS kcu
        ON tc.constraint_name = kcu.constraint_name
        AND tc.table_schema = kcu.table_schema
      JOIN information_schema.constraint_column_usage AS ccu
        ON ccu.constraint_name = tc.constraint_name
        AND ccu.table_schema = tc.table_schema
    WHERE constraint_type = 'FOREIGN KEY'
  SQL

  tuples = ActiveRecord::Base.connection.execute(query).values

  tuples.each_with_object(Hash.new([])) { |(k, v), r| r[k] |= [v] }
end