ActiveRecord's Insert Statement Generator

insert_statement_generator.rb

# frozen_string_literal: true

require "dry-initializer"

# Simply generates insert statement with optional overridings.
# === Usage:
#
#   like = Like.last
#   # => #<Like:0x00007f8a42b07858> {
#   #  :id         => "f93c47dc-9e09-4bf4-bbcb-2ec2000a873f",
#   #  :post_id    => "e70059b5-983c-4fb6-9aba-b5462c0192d4",
#   #  :user_id    => 34,
#   #  :deleted_at => nil,
#   #  :created_at => Tue, 10 Dec 2019 17:30:45 MSK +03:00,
#   #  :updated_at => Tue, 10 Dec 2019 17:30:45 MSK +03:00
#   # }
#   puts InsertStatementGenerator[like, user_id: 1]
#   # => INSERT INTO "likes" ("id", "post_id", "user_id", "deleted_at", "created_at", "updated_at")
#   #    VALUES ('f93c47dc-9e09-4bf4-bbcb-2ec2000a873f', 'e70059b5-983c-4fb6-9aba-b5462c0192d4', 1, NULL, '2019-12-10 14:30:45.348052', '2019-12-10 14:30:45.348052')
class InsertStatementGenerator
  extend Dry::Initializer

  class << self
    # :call-seq:
    #   InsertStatementGenerator[record, **override] → String
    #   InsertStatementGenerator.(record, **override) → String
    #   InsertStatementGenerator.call(record, **override) → String
    #
    # Generates a finel SQL +INSERT+ statement for the given record
    # and overrided values.
    def call(record, **override)
      new(record, override).to_sql
    end

    alias_method :[], :call
  end

  param :record, Types.Instance(ActiveRecord::Base)
  param :override, optional: true, default: -> { {} }

  # Returns Arel::InsertManager with a final statement
  def manager
    arel_table.compile_insert(values_for_insert)
  end

  # Returns a final SQL statement
  delegate :to_sql, to: :manager

  # Generates an associative array of column-value pairs with overrided values
  def values_for_insert
    record_attributes.map { |col, val| column_value(col, val) }
  end

  # Invokes +attributes_with_values_for_create+ for the record with it's attribute names
  def record_attributes
    record.send(:attributes_with_values_for_create, record.attribute_names)
  end

  private

  # Returns a single column-value pair with overrided value.
  def column_value(name, value)
    arel = arel_attribute(name)
    value = @override.fetch(name.to_sym, value)
    [arel, type_cast(arel, value)]
  end

  # Type casts value for a given column
  def type_cast(arel_attr, value)
    arel_attr.type_cast_for_database(value)
  end

  delegate :arel_table, :arel_attribute, to: "record.class"
end