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class ActiveRecord::Migration::CommandRecorder

Migration Command Recorder

ActiveRecord::Migration::CommandRecorder records commands done during a migration and knows how to reverse those commands. The CommandRecorder knows how to invert the following commands:

  • add_column

  • add_foreign_key

  • add_check_constraint

  • add_exclusion_constraint

  • add_unique_constraint

  • add_index

  • add_reference

  • add_timestamps

  • change_column_default (must supply a :from and :to option)

  • change_column_null

  • change_column_comment (must supply a :from and :to option)

  • change_table_comment (must supply a :from and :to option)

  • create_enum

  • create_join_table

  • create_virtual_table

  • create_table

  • disable_extension

  • drop_enum (must supply a list of values)

  • drop_join_table

  • drop_virtual_table (must supply options)

  • drop_table (must supply a block)

  • enable_extension

  • remove_column (must supply a type)

  • remove_columns (must supply a :type option)

  • remove_foreign_key (must supply a second table)

  • remove_check_constraint

  • remove_exclusion_constraint

  • remove_unique_constraint

  • remove_index

  • remove_reference

  • remove_timestamps

  • rename_column

  • rename_enum

  • rename_enum_value (must supply a :from and :to option)

  • rename_index

  • rename_table

Constants

ReversibleAndIrreversibleMethods

[
:create_table, :create_join_table, :rename_table, :add_column, :remove_column,
:rename_index, :rename_column, :add_index, :remove_index, :add_timestamps, :remove_timestamps,
:change_column_default, :add_reference, :remove_reference, :transaction,
:drop_join_table, :drop_table, :execute_block, :enable_extension, :disable_extension,
:change_column, :execute, :remove_columns, :change_column_null,
:add_foreign_key, :remove_foreign_key,
:change_column_comment, :change_table_comment,
:add_check_constraint, :remove_check_constraint,
:add_exclusion_constraint, :remove_exclusion_constraint,
:add_unique_constraint, :remove_unique_constraint,
:create_enum, :drop_enum, :rename_enum, :add_enum_value, :rename_enum_value,
:create_schema, :drop_schema,
:create_virtual_table, :drop_virtual_table
]

Attributes

[RW] commands
[RW] delegate
[RW] reverting

Public class methods

new(delegate = nil)

Source code GitHub 
# File activerecord/lib/active_record/migration/command_recorder.rb, line 67
def initialize(delegate = nil)
  @commands = []
  @delegate = delegate
  @reverting = false
end

Public instance methods

inverse_of(command, args, &block)

Returns the inverse of the given command. For example:

recorder.inverse_of(:rename_table, [:old, :new])
# => [:rename_table, [:new, :old]]

If the inverse of a command requires several commands, returns array of commands.

recorder.inverse_of(:remove_columns, [:some_table, :foo, :bar, type: :string])
# => [[:add_column, :some_table, :foo, :string], [:add_column, :some_table, :bar, :string]]

This method will raise an IrreversibleMigration exception if it cannot invert the command.

Source code GitHub 
# File activerecord/lib/active_record/migration/command_recorder.rb, line 114
      def inverse_of(command, args, &block)
        method = :"invert_#{command}"
        raise IrreversibleMigration, <<~MSG unless respond_to?(method, true)
          This migration uses #{command}, which is not automatically reversible.
          To make the migration reversible you can either:
          1. Define #up and #down methods in place of the #change method.
          2. Use the #reversible method to define reversible behavior.
        MSG
        send(method, args, &block)
      end

record(*command, &block)

Record command. command should be a method name and arguments. For example:

recorder.record(:method_name, [:arg1, :arg2])
Source code GitHub 
# File activerecord/lib/active_record/migration/command_recorder.rb, line 94
def record(*command, &block)
  if @reverting
    @commands << inverse_of(*command, &block)
  else
    @commands << (command << block)
  end
end

replay(migration)

Source code GitHub 
# File activerecord/lib/active_record/migration/command_recorder.rb, line 148
def replay(migration)
  commands.each do |cmd, args, block|
    migration.send(cmd, *args, &block)
  end
end

revert()

While executing the given block, the recorded will be in reverting mode. All commands recorded will end up being recorded reverted and in reverse order. For example:

recorder.revert{ recorder.record(:rename_table, [:old, :new]) }
# same effect as recorder.record(:rename_table, [:new, :old])
Source code GitHub 
# File activerecord/lib/active_record/migration/command_recorder.rb, line 80
def revert
  @reverting = !@reverting
  previous = @commands
  @commands = []
  yield
ensure
  @commands = previous.concat(@commands.reverse)
  @reverting = !@reverting
end

Definition files