The lowest-overhead way to get all tables & columns out of an ActiveRecord db/schema.rb

minimal-schema-loader.rb

#!/usr/bin/env ruby
# frozen_string_literal: true

module Nop
  def nop(*methods)
    methods.each do |method|
      define_method(method) { |*_args| nil }
    end
  end
end

# A simple stub that collects the information in a Rails db/schema.rb file
class FakeSchemaDSL
  extend Nop

  def initialize(info)
    @info = info
    @tables = {}
  end

  def create_table(name, **opts)
    raise 'block is required' unless block_given?

    t = @tables[name] = TableHelper.new(opts)
    yield t
  end

  attr_reader :tables

  nop :enable_extension, :add_foreign_key

  class TableHelper
    extend Nop

    nop :index

    def initialize(opts)
      @table_opts = opts
      @columns = {}
    end

    attr_reader :columns

    def respond_to_missing?(_name, _include_private = true)
      true
    end

    def method_missing(type, column_name, **opts)
      @columns[column_name] = { type: type, opts: opts }
    end
  end
end

module ActiveRecord
  class Schema
    def self.define(info, &block)
      raise '#define called twice' if @dsl

      @dsl = FakeSchemaDSL.new(info)
      @dsl.instance_eval(&block)
    end

    def self.tables
      @dsl.tables
    end
  end
end

require_relative '../db/schema' or abort 'noooo'

require 'pp'

pp ActiveRecord::Schema.tables.transform_values(&:columns)